chore: switch database engine to sqlite (fixes #9954) (#9965)

Switch the database from LevelDB to SQLite, for greater stability and
simpler code.

Co-authored-by: Tommy van der Vorst <tommy@pixelspark.nl>
Co-authored-by: bt90 <btom1990@googlemail.com>

internal/db/sqlite/db.go

@@ -0,0 +1,77 @@
+// Copyright (C) 2025 The Syncthing Authors.
+//
+// This Source Code Form is subject to the terms of the Mozilla Public
+// License, v. 2.0. If a copy of the MPL was not distributed with this file,
+// You can obtain one at https://mozilla.org/MPL/2.0/.
+
+package sqlite
+
+import (
+	"sync"
+	"time"
+
+	"github.com/jmoiron/sqlx"
+	"github.com/syncthing/syncthing/internal/db"
+	"github.com/syncthing/syncthing/lib/protocol"
+	"github.com/thejerf/suture/v4"
+)
+
+type DB struct {
+	sql            *sqlx.DB
+	localDeviceIdx int64
+	updateLock     sync.Mutex
+
+	statementsMut sync.RWMutex
+	statements    map[string]*sqlx.Stmt
+	tplInput      map[string]any
+}
+
+var _ db.DB = (*DB)(nil)
+
+func (s *DB) Close() error {
+	s.updateLock.Lock()
+	s.statementsMut.Lock()
+	defer s.updateLock.Unlock()
+	defer s.statementsMut.Unlock()
+	for _, stmt := range s.statements {
+		stmt.Close()
+	}
+	return wrap(s.sql.Close())
+}
+
+func (s *DB) Service(maintenanceInterval time.Duration) suture.Service {
+	return newService(s, maintenanceInterval)
+}
+
+func (s *DB) ListFolders() ([]string, error) {
+	var res []string
+	err := s.stmt(`
+		SELECT folder_id FROM folders
+		ORDER BY folder_id
+	`).Select(&res)
+	return res, wrap(err)
+}
+
+func (s *DB) ListDevicesForFolder(folder string) ([]protocol.DeviceID, error) {
+	var res []string
+	err := s.stmt(`
+		SELECT d.device_id FROM counts s
+		INNER JOIN folders o ON o.idx = s.folder_idx
+		INNER JOIN devices d ON d.idx = s.device_idx
+		WHERE o.folder_id = ? AND s.count > 0 AND s.device_idx != {{.LocalDeviceIdx}}
+		GROUP BY d.device_id
+		ORDER BY d.device_id
+	`).Select(&res, folder)
+	if err != nil {
+		return nil, wrap(err)
+	}
+
+	devs := make([]protocol.DeviceID, len(res))
+	for i, s := range res {
+		devs[i], err = protocol.DeviceIDFromString(s)
+		if err != nil {
+			return nil, wrap(err)
+		}
+	}
+	return devs, nil
+}

internal/db/sqlite/db_bench_test.go

@@ -0,0 +1,243 @@
+// Copyright (C) 2025 The Syncthing Authors.
+//
+// This Source Code Form is subject to the terms of the Mozilla Public
+// License, v. 2.0. If a copy of the MPL was not distributed with this file,
+// You can obtain one at https://mozilla.org/MPL/2.0/.
+
+package sqlite
+
+import (
+	"context"
+	"fmt"
+	"testing"
+	"time"
+
+	"github.com/syncthing/syncthing/internal/timeutil"
+	"github.com/syncthing/syncthing/lib/config"
+	"github.com/syncthing/syncthing/lib/protocol"
+	"github.com/syncthing/syncthing/lib/rand"
+)
+
+var globalFi protocol.FileInfo
+
+func BenchmarkUpdate(b *testing.B) {
+	db, err := OpenTemp()
+	if err != nil {
+		b.Fatal(err)
+	}
+	b.Cleanup(func() {
+		if err := db.Close(); err != nil {
+			b.Fatal(err)
+		}
+	})
+	svc := db.Service(time.Hour).(*Service)
+
+	fs := make([]protocol.FileInfo, 100)
+	seed := 0
+
+	size := 10000
+	for size < 200_000 {
+		t0 := time.Now()
+		if err := svc.periodic(context.Background()); err != nil {
+			b.Fatal(err)
+		}
+		b.Log("garbage collect in", time.Since(t0))
+
+		for {
+			local, err := db.CountLocal(folderID, protocol.LocalDeviceID)
+			if err != nil {
+				b.Fatal(err)
+			}
+			if local.Files >= size {
+				break
+			}
+			fs := make([]protocol.FileInfo, 1000)
+			for i := range fs {
+				fs[i] = genFile(rand.String(24), 64, 0)
+			}
+			if err := db.Update(folderID, protocol.LocalDeviceID, fs); err != nil {
+				b.Fatal(err)
+			}
+		}
+
+		b.Run(fmt.Sprintf("Insert100Loc@%d", size), func(b *testing.B) {
+			for range b.N {
+				for i := range fs {
+					fs[i] = genFile(rand.String(24), 64, 0)
+				}
+				if err := db.Update(folderID, protocol.LocalDeviceID, fs); err != nil {
+					b.Fatal(err)
+				}
+			}
+			b.ReportMetric(float64(b.N)*100.0/b.Elapsed().Seconds(), "files/s")
+		})
+
+		b.Run(fmt.Sprintf("RepBlocks100@%d", size), func(b *testing.B) {
+			for range b.N {
+				for i := range fs {
+					fs[i].Blocks = genBlocks(fs[i].Name, seed, 64)
+					fs[i].Version = fs[i].Version.Update(42)
+				}
+				seed++
+				if err := db.Update(folderID, protocol.LocalDeviceID, fs); err != nil {
+					b.Fatal(err)
+				}
+			}
+			b.ReportMetric(float64(b.N)*100.0/b.Elapsed().Seconds(), "files/s")
+		})
+
+		b.Run(fmt.Sprintf("RepSame100@%d", size), func(b *testing.B) {
+			for range b.N {
+				for i := range fs {
+					fs[i].Version = fs[i].Version.Update(42)
+				}
+				if err := db.Update(folderID, protocol.LocalDeviceID, fs); err != nil {
+					b.Fatal(err)
+				}
+			}
+			b.ReportMetric(float64(b.N)*100.0/b.Elapsed().Seconds(), "files/s")
+		})
+
+		b.Run(fmt.Sprintf("Insert100Rem@%d", size), func(b *testing.B) {
+			for range b.N {
+				for i := range fs {
+					fs[i].Blocks = genBlocks(fs[i].Name, seed, 64)
+					fs[i].Version = fs[i].Version.Update(42)
+					fs[i].Sequence = timeutil.StrictlyMonotonicNanos()
+				}
+				if err := db.Update(folderID, protocol.DeviceID{42}, fs); err != nil {
+					b.Fatal(err)
+				}
+			}
+			b.ReportMetric(float64(b.N)*100.0/b.Elapsed().Seconds(), "files/s")
+		})
+
+		b.Run(fmt.Sprintf("GetGlobal100@%d", size), func(b *testing.B) {
+			for range b.N {
+				for i := range fs {
+					_, ok, err := db.GetGlobalFile(folderID, fs[i].Name)
+					if err != nil {
+						b.Fatal(err)
+					}
+					if !ok {
+						b.Fatal("should exist")
+					}
+				}
+			}
+			b.ReportMetric(float64(b.N)*100.0/b.Elapsed().Seconds(), "files/s")
+		})
+
+		b.Run(fmt.Sprintf("LocalSequenced@%d", size), func(b *testing.B) {
+			count := 0
+			for range b.N {
+				cur, err := db.GetDeviceSequence(folderID, protocol.LocalDeviceID)
+				if err != nil {
+					b.Fatal(err)
+				}
+				it, errFn := db.AllLocalFilesBySequence(folderID, protocol.LocalDeviceID, cur-100, 0)
+				for f := range it {
+					count++
+					globalFi = f
+				}
+				if err := errFn(); err != nil {
+					b.Fatal(err)
+				}
+			}
+			b.ReportMetric(float64(count)/b.Elapsed().Seconds(), "files/s")
+		})
+
+		b.Run(fmt.Sprintf("GetDeviceSequenceLoc@%d", size), func(b *testing.B) {
+			for range b.N {
+				_, err := db.GetDeviceSequence(folderID, protocol.LocalDeviceID)
+				if err != nil {
+					b.Fatal(err)
+				}
+			}
+		})
+		b.Run(fmt.Sprintf("GetDeviceSequenceRem@%d", size), func(b *testing.B) {
+			for range b.N {
+				_, err := db.GetDeviceSequence(folderID, protocol.DeviceID{42})
+				if err != nil {
+					b.Fatal(err)
+				}
+			}
+		})
+
+		b.Run(fmt.Sprintf("RemoteNeed@%d", size), func(b *testing.B) {
+			count := 0
+			for range b.N {
+				it, errFn := db.AllNeededGlobalFiles(folderID, protocol.DeviceID{42}, config.PullOrderAlphabetic, 0, 0)
+				for f := range it {
+					count++
+					globalFi = f
+				}
+				if err := errFn(); err != nil {
+					b.Fatal(err)
+				}
+			}
+			b.ReportMetric(float64(count)/b.Elapsed().Seconds(), "files/s")
+		})
+
+		b.Run(fmt.Sprintf("LocalNeed100Largest@%d", size), func(b *testing.B) {
+			count := 0
+			for range b.N {
+				it, errFn := db.AllNeededGlobalFiles(folderID, protocol.LocalDeviceID, config.PullOrderLargestFirst, 100, 0)
+				for f := range it {
+					globalFi = f
+					count++
+				}
+				if err := errFn(); err != nil {
+					b.Fatal(err)
+				}
+			}
+			b.ReportMetric(float64(count)/b.Elapsed().Seconds(), "files/s")
+		})
+
+		size <<= 1
+	}
+}
+
+func TestBenchmarkDropAllRemote(t *testing.T) {
+	if testing.Short() {
+		t.Skip("slow test")
+	}
+
+	db, err := OpenTemp()
+	if err != nil {
+		t.Fatal(err)
+	}
+	t.Cleanup(func() {
+		if err := db.Close(); err != nil {
+			t.Fatal(err)
+		}
+	})
+
+	fs := make([]protocol.FileInfo, 1000)
+	seq := 0
+	for {
+		local, err := db.CountLocal(folderID, protocol.LocalDeviceID)
+		if err != nil {
+			t.Fatal(err)
+		}
+		if local.Files >= 15_000 {
+			break
+		}
+		for i := range fs {
+			seq++
+			fs[i] = genFile(rand.String(24), 64, seq)
+		}
+		if err := db.Update(folderID, protocol.DeviceID{42}, fs); err != nil {
+			t.Fatal(err)
+		}
+		if err := db.Update(folderID, protocol.LocalDeviceID, fs); err != nil {
+			t.Fatal(err)
+		}
+	}
+
+	t0 := time.Now()
+	if err := db.DropAllFiles(folderID, protocol.DeviceID{42}); err != nil {
+		t.Fatal(err)
+	}
+	d := time.Since(t0)
+	t.Log("drop all took", d)
+}

internal/db/sqlite/db_counts.go

@@ -0,0 +1,137 @@
+// Copyright (C) 2025 The Syncthing Authors.
+//
+// This Source Code Form is subject to the terms of the Mozilla Public
+// License, v. 2.0. If a copy of the MPL was not distributed with this file,
+// You can obtain one at https://mozilla.org/MPL/2.0/.
+
+package sqlite
+
+import (
+	"github.com/syncthing/syncthing/internal/db"
+	"github.com/syncthing/syncthing/lib/protocol"
+)
+
+type countsRow struct {
+	Type       protocol.FileInfoType
+	Count      int
+	Size       int64
+	Deleted    bool
+	LocalFlags int64 `db:"local_flags"`
+}
+
+func (s *DB) CountLocal(folder string, device protocol.DeviceID) (db.Counts, error) {
+	var res []countsRow
+	if err := s.stmt(`
+		SELECT s.type, s.count, s.size, s.local_flags, s.deleted FROM counts s
+		INNER JOIN folders o ON o.idx = s.folder_idx
+		INNER JOIN devices d ON d.idx = s.device_idx
+		WHERE o.folder_id = ? AND d.device_id = ? AND s.local_flags & {{.FlagLocalIgnored}} = 0
+	`).Select(&res, folder, device.String()); err != nil {
+		return db.Counts{}, wrap(err)
+	}
+	return summarizeCounts(res), nil
+}
+
+func (s *DB) CountNeed(folder string, device protocol.DeviceID) (db.Counts, error) {
+	if device == protocol.LocalDeviceID {
+		return s.needSizeLocal(folder)
+	}
+	return s.needSizeRemote(folder, device)
+}
+
+func (s *DB) CountGlobal(folder string) (db.Counts, error) {
+	// Exclude ignored and receive-only changed files from the global count
+	// (legacy expectation? it's a bit weird since those files can in fact
+	// be global and you can get them with GetGlobal etc.)
+	var res []countsRow
+	err := s.stmt(`
+		SELECT s.type, s.count, s.size, s.local_flags, s.deleted FROM counts s
+		INNER JOIN folders o ON o.idx = s.folder_idx
+		WHERE o.folder_id = ? AND s.local_flags & {{.FlagLocalGlobal}} != 0 AND s.local_flags & {{or .FlagLocalReceiveOnly .FlagLocalIgnored}} = 0
+	`).Select(&res, folder)
+	if err != nil {
+		return db.Counts{}, wrap(err)
+	}
+	return summarizeCounts(res), nil
+}
+
+func (s *DB) CountReceiveOnlyChanged(folder string) (db.Counts, error) {
+	var res []countsRow
+	err := s.stmt(`
+		SELECT s.type, s.count, s.size, s.local_flags, s.deleted FROM counts s
+		INNER JOIN folders o ON o.idx = s.folder_idx
+		WHERE o.folder_id = ? AND local_flags & {{.FlagLocalReceiveOnly}} != 0
+	`).Select(&res, folder)
+	if err != nil {
+		return db.Counts{}, wrap(err)
+	}
+	return summarizeCounts(res), nil
+}
+
+func (s *DB) needSizeLocal(folder string) (db.Counts, error) {
+	// The need size for the local device is the sum of entries with the
+	// need bit set.
+	var res []countsRow
+	err := s.stmt(`
+		SELECT s.type, s.count, s.size, s.local_flags, s.deleted FROM counts s
+		INNER JOIN folders o ON o.idx = s.folder_idx
+		WHERE o.folder_id = ? AND s.local_flags & {{.FlagLocalNeeded}} != 0
+	`).Select(&res, folder)
+	if err != nil {
+		return db.Counts{}, wrap(err)
+	}
+	return summarizeCounts(res), nil
+}
+
+func (s *DB) needSizeRemote(folder string, device protocol.DeviceID) (db.Counts, error) {
+	var res []countsRow
+	// See neededGlobalFilesRemote for commentary as that is the same query without summing
+	if err := s.stmt(`
+		SELECT g.type, count(*) as count, sum(g.size) as size, g.local_flags, g.deleted FROM files g
+		INNER JOIN folders o ON o.idx = g.folder_idx
+		WHERE o.folder_id = ? AND g.local_flags & {{.FlagLocalGlobal}} != 0 AND NOT g.deleted AND NOT g.invalid AND NOT EXISTS (
+			SELECT 1 FROM FILES f
+			INNER JOIN devices d ON d.idx = f.device_idx
+			WHERE f.name = g.name AND f.version = g.version AND f.folder_idx = g.folder_idx AND d.device_id = ?
+		)
+		GROUP BY g.type, g.local_flags, g.deleted
+
+		UNION ALL
+
+		SELECT g.type, count(*) as count, sum(g.size) as size, g.local_flags, g.deleted FROM files g
+		INNER JOIN folders o ON o.idx = g.folder_idx
+		WHERE o.folder_id = ? AND g.local_flags & {{.FlagLocalGlobal}} != 0 AND g.deleted AND NOT g.invalid AND EXISTS (
+			SELECT 1 FROM FILES f
+			INNER JOIN devices d ON d.idx = f.device_idx
+			WHERE f.name = g.name AND f.folder_idx = g.folder_idx AND d.device_id = ? AND NOT f.deleted
+		)
+		GROUP BY g.type, g.local_flags, g.deleted
+	`).Select(&res, folder, device.String(),
+		folder, device.String()); err != nil {
+		return db.Counts{}, wrap(err)
+	}
+
+	return summarizeCounts(res), nil
+}
+
+func summarizeCounts(res []countsRow) db.Counts {
+	c := db.Counts{
+		DeviceID: protocol.LocalDeviceID,
+	}
+	for _, r := range res {
+		switch {
+		case r.Deleted:
+			c.Deleted += r.Count
+		case r.Type == protocol.FileInfoTypeFile:
+			c.Files += r.Count
+			c.Bytes += r.Size
+		case r.Type == protocol.FileInfoTypeDirectory:
+			c.Directories += r.Count
+			c.Bytes += r.Size
+		case r.Type == protocol.FileInfoTypeSymlink:
+			c.Symlinks += r.Count
+			c.Bytes += r.Size
+		}
+	}
+	return c
+}

internal/db/sqlite/db_global.go

@@ -0,0 +1,189 @@
+// Copyright (C) 2025 The Syncthing Authors.
+//
+// This Source Code Form is subject to the terms of the Mozilla Public
+// License, v. 2.0. If a copy of the MPL was not distributed with this file,
+// You can obtain one at https://mozilla.org/MPL/2.0/.
+
+package sqlite
+
+import (
+	"database/sql"
+	"errors"
+	"fmt"
+	"iter"
+
+	"github.com/syncthing/syncthing/internal/db"
+	"github.com/syncthing/syncthing/internal/itererr"
+	"github.com/syncthing/syncthing/lib/config"
+	"github.com/syncthing/syncthing/lib/osutil"
+	"github.com/syncthing/syncthing/lib/protocol"
+)
+
+func (s *DB) GetGlobalFile(folder string, file string) (protocol.FileInfo, bool, error) {
+	file = osutil.NormalizedFilename(file)
+
+	var ind indirectFI
+	err := s.stmt(`
+		SELECT fi.fiprotobuf, bl.blprotobuf FROM fileinfos fi
+		INNER JOIN files f on fi.sequence = f.sequence
+		LEFT JOIN blocklists bl ON bl.blocklist_hash = f.blocklist_hash
+		INNER JOIN folders o ON o.idx = f.folder_idx
+		WHERE o.folder_id = ? AND f.name = ? AND f.local_flags & {{.FlagLocalGlobal}} != 0
+	`).Get(&ind, folder, file)
+	if errors.Is(err, sql.ErrNoRows) {
+		return protocol.FileInfo{}, false, nil
+	}
+	if err != nil {
+		return protocol.FileInfo{}, false, wrap(err)
+	}
+	fi, err := ind.FileInfo()
+	if err != nil {
+		return protocol.FileInfo{}, false, wrap(err)
+	}
+	return fi, true, nil
+}
+
+func (s *DB) GetGlobalAvailability(folder, file string) ([]protocol.DeviceID, error) {
+	file = osutil.NormalizedFilename(file)
+
+	var devStrs []string
+	err := s.stmt(`
+		SELECT d.device_id FROM files f
+		INNER JOIN devices d ON d.idx = f.device_idx
+		INNER JOIN folders o ON o.idx = f.folder_idx
+		INNER JOIN files g ON f.folder_idx = g.folder_idx AND g.version = f.version AND g.name = f.name
+		WHERE o.folder_id = ? AND g.name = ? AND g.local_flags & {{.FlagLocalGlobal}} != 0 AND f.device_idx != {{.LocalDeviceIdx}}
+		ORDER BY d.device_id
+	`).Select(&devStrs, folder, file)
+	if errors.Is(err, sql.ErrNoRows) {
+		return nil, nil
+	}
+	if err != nil {
+		return nil, wrap(err)
+	}
+
+	devs := make([]protocol.DeviceID, 0, len(devStrs))
+	for _, s := range devStrs {
+		d, err := protocol.DeviceIDFromString(s)
+		if err != nil {
+			return nil, wrap(err)
+		}
+		devs = append(devs, d)
+	}
+
+	return devs, nil
+}
+
+func (s *DB) AllGlobalFiles(folder string) (iter.Seq[db.FileMetadata], func() error) {
+	it, errFn := iterStructs[db.FileMetadata](s.stmt(`
+		SELECT f.sequence, f.name, f.type, f.modified as modnanos, f.size, f.deleted, f.invalid, f.local_flags as localflags FROM files f
+		INNER JOIN folders o ON o.idx = f.folder_idx
+		WHERE o.folder_id = ? AND f.local_flags & {{.FlagLocalGlobal}} != 0
+		ORDER BY f.name
+	`).Queryx(folder))
+	return itererr.Map(it, errFn, func(m db.FileMetadata) (db.FileMetadata, error) {
+		m.Name = osutil.NativeFilename(m.Name)
+		return m, nil
+	})
+}
+
+func (s *DB) AllGlobalFilesPrefix(folder string, prefix string) (iter.Seq[db.FileMetadata], func() error) {
+	if prefix == "" {
+		return s.AllGlobalFiles(folder)
+	}
+
+	prefix = osutil.NormalizedFilename(prefix)
+	end := prefixEnd(prefix)
+
+	it, errFn := iterStructs[db.FileMetadata](s.stmt(`
+		SELECT f.sequence, f.name, f.type, f.modified as modnanos, f.size, f.deleted, f.invalid, f.local_flags as localflags FROM files f
+		INNER JOIN folders o ON o.idx = f.folder_idx
+		WHERE o.folder_id = ? AND f.name >= ? AND f.name < ? AND f.local_flags & {{.FlagLocalGlobal}} != 0
+		ORDER BY f.name
+	`).Queryx(folder, prefix, end))
+	return itererr.Map(it, errFn, func(m db.FileMetadata) (db.FileMetadata, error) {
+		m.Name = osutil.NativeFilename(m.Name)
+		return m, nil
+	})
+}
+
+func (s *DB) AllNeededGlobalFiles(folder string, device protocol.DeviceID, order config.PullOrder, limit, offset int) (iter.Seq[protocol.FileInfo], func() error) {
+	var selectOpts string
+	switch order {
+	case config.PullOrderRandom:
+		selectOpts = "ORDER BY RANDOM()"
+	case config.PullOrderAlphabetic:
+		selectOpts = "ORDER BY g.name ASC"
+	case config.PullOrderSmallestFirst:
+		selectOpts = "ORDER BY g.size ASC"
+	case config.PullOrderLargestFirst:
+		selectOpts = "ORDER BY g.size DESC"
+	case config.PullOrderOldestFirst:
+		selectOpts = "ORDER BY g.modified ASC"
+	case config.PullOrderNewestFirst:
+		selectOpts = "ORDER BY g.modified DESC"
+	}
+
+	if limit > 0 {
+		selectOpts += fmt.Sprintf(" LIMIT %d", limit)
+	}
+	if offset > 0 {
+		selectOpts += fmt.Sprintf(" OFFSET %d", offset)
+	}
+
+	if device == protocol.LocalDeviceID {
+		return s.neededGlobalFilesLocal(folder, selectOpts)
+	}
+
+	return s.neededGlobalFilesRemote(folder, device, selectOpts)
+}
+
+func (s *DB) neededGlobalFilesLocal(folder, selectOpts string) (iter.Seq[protocol.FileInfo], func() error) {
+	// Select all the non-ignored files with the need bit set.
+	it, errFn := iterStructs[indirectFI](s.stmt(`
+		SELECT fi.fiprotobuf, bl.blprotobuf, g.name, g.size, g.modified FROM fileinfos fi
+		INNER JOIN files g on fi.sequence = g.sequence
+		LEFT JOIN blocklists bl ON bl.blocklist_hash = g.blocklist_hash
+		INNER JOIN folders o ON o.idx = g.folder_idx
+		WHERE o.folder_id = ? AND g.local_flags & {{.FlagLocalIgnored}} = 0 AND g.local_flags & {{.FlagLocalNeeded}} != 0
+	` + selectOpts).Queryx(folder))
+	return itererr.Map(it, errFn, indirectFI.FileInfo)
+}
+
+func (s *DB) neededGlobalFilesRemote(folder string, device protocol.DeviceID, selectOpts string) (iter.Seq[protocol.FileInfo], func() error) {
+	// Select:
+	//
+	// - all the valid, non-deleted global files that don't have a corresponding
+	//   remote file with the same version.
+	//
+	// - all the valid, deleted global files that have a corresponding non-deleted
+	//   remote file (of any version)
+
+	it, errFn := iterStructs[indirectFI](s.stmt(`
+		SELECT fi.fiprotobuf, bl.blprotobuf, g.name, g.size, g.modified FROM fileinfos fi
+		INNER JOIN files g on fi.sequence = g.sequence
+		LEFT JOIN blocklists bl ON bl.blocklist_hash = g.blocklist_hash
+		INNER JOIN folders o ON o.idx = g.folder_idx
+		WHERE o.folder_id = ? AND g.local_flags & {{.FlagLocalGlobal}} != 0 AND NOT g.deleted AND NOT g.invalid AND NOT EXISTS (
+			SELECT 1 FROM FILES f
+			INNER JOIN devices d ON d.idx = f.device_idx
+			WHERE f.name = g.name AND f.version = g.version AND f.folder_idx = g.folder_idx AND d.device_id = ?
+		)
+
+		UNION ALL
+
+		SELECT fi.fiprotobuf, bl.blprotobuf, g.name, g.size, g.modified FROM fileinfos fi
+		INNER JOIN files g on fi.sequence = g.sequence
+		LEFT JOIN blocklists bl ON bl.blocklist_hash = g.blocklist_hash
+		INNER JOIN folders o ON o.idx = g.folder_idx
+		WHERE o.folder_id = ? AND g.local_flags & {{.FlagLocalGlobal}} != 0 AND g.deleted AND NOT g.invalid AND EXISTS (
+			SELECT 1 FROM FILES f
+			INNER JOIN devices d ON d.idx = f.device_idx
+			WHERE f.name = g.name AND f.folder_idx = g.folder_idx AND d.device_id = ? AND NOT f.deleted
+		)
+	`+selectOpts).Queryx(
+		folder, device.String(),
+		folder, device.String(),
+	))
+	return itererr.Map(it, errFn, indirectFI.FileInfo)
+}

internal/db/sqlite/db_global_test.go

@@ -0,0 +1,493 @@
+// Copyright (C) 2025 The Syncthing Authors.
+//
+// This Source Code Form is subject to the terms of the Mozilla Public
+// License, v. 2.0. If a copy of the MPL was not distributed with this file,
+// You can obtain one at https://mozilla.org/MPL/2.0/.
+
+package sqlite
+
+import (
+	"slices"
+	"testing"
+
+	"github.com/syncthing/syncthing/lib/config"
+	"github.com/syncthing/syncthing/lib/protocol"
+)
+
+func TestNeed(t *testing.T) {
+	t.Helper()
+
+	db, err := OpenTemp()
+	if err != nil {
+		t.Fatal(err)
+	}
+	t.Cleanup(func() {
+		if err := db.Close(); err != nil {
+			t.Fatal(err)
+		}
+	})
+
+	// Some local files
+	var v protocol.Vector
+	baseV := v.Update(1)
+	newerV := baseV.Update(42)
+	files := []protocol.FileInfo{
+		genFile("test1", 1, 0), // remote need
+		genFile("test2", 2, 0), // local need
+		genFile("test3", 3, 0), // global
+	}
+	files[0].Version = baseV
+	files[1].Version = baseV
+	files[2].Version = newerV
+	err = db.Update(folderID, protocol.LocalDeviceID, files)
+	if err != nil {
+		t.Fatal(err)
+	}
+
+	// Some remote files
+	remote := []protocol.FileInfo{
+		genFile("test2", 2, 100), // global
+		genFile("test3", 3, 101), // remote need
+		genFile("test4", 4, 102), // local need
+	}
+	remote[0].Version = newerV
+	remote[1].Version = baseV
+	remote[2].Version = newerV
+	err = db.Update(folderID, protocol.DeviceID{42}, remote)
+	if err != nil {
+		t.Fatal(err)
+	}
+
+	// A couple are needed locally
+	localNeed := fiNames(mustCollect[protocol.FileInfo](t)(db.AllNeededGlobalFiles(folderID, protocol.LocalDeviceID, config.PullOrderAlphabetic, 0, 0)))
+	if !slices.Equal(localNeed, []string{"test2", "test4"}) {
+		t.Log(localNeed)
+		t.Fatal("bad local need")
+	}
+
+	// Another couple are needed remotely
+	remoteNeed := fiNames(mustCollect[protocol.FileInfo](t)(db.AllNeededGlobalFiles(folderID, protocol.DeviceID{42}, config.PullOrderAlphabetic, 0, 0)))
+	if !slices.Equal(remoteNeed, []string{"test1", "test3"}) {
+		t.Log(remoteNeed)
+		t.Fatal("bad remote need")
+	}
+}
+
+func TestDropRecalcsGlobal(t *testing.T) {
+	// When we drop a device we may get a new global
+
+	t.Parallel()
+
+	t.Run("DropAllFiles", func(t *testing.T) {
+		t.Parallel()
+
+		testDropWithDropper(t, func(t *testing.T, db *DB) {
+			t.Helper()
+			if err := db.DropAllFiles(folderID, protocol.DeviceID{42}); err != nil {
+				t.Fatal(err)
+			}
+		})
+	})
+
+	t.Run("DropDevice", func(t *testing.T) {
+		t.Parallel()
+
+		testDropWithDropper(t, func(t *testing.T, db *DB) {
+			t.Helper()
+			if err := db.DropDevice(protocol.DeviceID{42}); err != nil {
+				t.Fatal(err)
+			}
+		})
+	})
+
+	t.Run("DropFilesNamed", func(t *testing.T) {
+		t.Parallel()
+
+		testDropWithDropper(t, func(t *testing.T, db *DB) {
+			t.Helper()
+			if err := db.DropFilesNamed(folderID, protocol.DeviceID{42}, []string{"test1", "test42"}); err != nil {
+				t.Fatal(err)
+			}
+		})
+	})
+}
+
+func testDropWithDropper(t *testing.T, dropper func(t *testing.T, db *DB)) {
+	t.Helper()
+
+	db, err := OpenTemp()
+	if err != nil {
+		t.Fatal(err)
+	}
+	t.Cleanup(func() {
+		if err := db.Close(); err != nil {
+			t.Fatal(err)
+		}
+	})
+
+	// Some local files
+	err = db.Update(folderID, protocol.LocalDeviceID, []protocol.FileInfo{
+		genFile("test1", 1, 0),
+		genFile("test2", 2, 0),
+	})
+	if err != nil {
+		t.Fatal(err)
+	}
+
+	// Some remote files
+	remote := []protocol.FileInfo{
+		genFile("test1", 3, 0),
+	}
+	remote[0].Version = remote[0].Version.Update(42)
+	err = db.Update(folderID, protocol.DeviceID{42}, remote)
+	if err != nil {
+		t.Fatal(err)
+	}
+
+	// Remote test1 wins as the global, verify.
+	count, err := db.CountGlobal(folderID)
+	if err != nil {
+		t.Fatal(err)
+	}
+	if count.Bytes != (2+3)*128<<10 {
+		t.Log(count)
+		t.Fatal("bad global size to begin with")
+	}
+	if g, ok, err := db.GetGlobalFile(folderID, "test1"); err != nil || !ok {
+		t.Fatal("missing global to begin with")
+	} else if g.Size != 3*128<<10 {
+		t.Fatal("remote test1 should be the global")
+	}
+
+	// Now remove that remote device
+	dropper(t, db)
+
+	// Our test1 should now be the global
+	count, err = db.CountGlobal(folderID)
+	if err != nil {
+		t.Fatal(err)
+	}
+	if count.Bytes != (1+2)*128<<10 {
+		t.Log(count)
+		t.Fatal("bad global size after drop")
+	}
+	if g, ok, err := db.GetGlobalFile(folderID, "test1"); err != nil || !ok {
+		t.Fatal("missing global after drop")
+	} else if g.Size != 1*128<<10 {
+		t.Fatal("local test1 should be the global")
+	}
+}
+
+func TestNeedDeleted(t *testing.T) {
+	t.Parallel()
+
+	db, err := OpenTemp()
+	if err != nil {
+		t.Fatal(err)
+	}
+	t.Cleanup(func() {
+		if err := db.Close(); err != nil {
+			t.Fatal(err)
+		}
+	})
+
+	// Some local files
+	err = db.Update(folderID, protocol.LocalDeviceID, []protocol.FileInfo{
+		genFile("test1", 1, 0),
+		genFile("test2", 2, 0),
+	})
+	if err != nil {
+		t.Fatal(err)
+	}
+
+	// A remote deleted file
+	remote := []protocol.FileInfo{
+		genFile("test1", 1, 101),
+	}
+	remote[0].SetDeleted(42)
+	err = db.Update(folderID, protocol.DeviceID{42}, remote)
+	if err != nil {
+		t.Fatal(err)
+	}
+
+	// We need the one deleted file
+	s, err := db.CountNeed(folderID, protocol.LocalDeviceID)
+	if err != nil {
+		t.Fatal(err)
+	}
+	if s.Bytes != 0 || s.Deleted != 1 {
+		t.Log(s)
+		t.Error("bad need")
+	}
+}
+
+func TestDontNeedIgnored(t *testing.T) {
+	t.Parallel()
+
+	db, err := OpenTemp()
+	if err != nil {
+		t.Fatal(err)
+	}
+	t.Cleanup(func() {
+		if err := db.Close(); err != nil {
+			t.Fatal(err)
+		}
+	})
+
+	// A remote file
+	files := []protocol.FileInfo{
+		genFile("test1", 1, 103),
+	}
+	err = db.Update(folderID, protocol.DeviceID{42}, files)
+	if err != nil {
+		t.Fatal(err)
+	}
+
+	// Which we've ignored locally
+	files[0].SetIgnored()
+	err = db.Update(folderID, protocol.LocalDeviceID, files)
+	if err != nil {
+		t.Fatal(err)
+	}
+
+	// We don't need it
+	s, err := db.CountNeed(folderID, protocol.LocalDeviceID)
+	if err != nil {
+		t.Fatal(err)
+	}
+	if s.Bytes != 0 || s.Files != 0 {
+		t.Log(s)
+		t.Error("bad need")
+	}
+
+	// It shouldn't show up in the need list
+	names := mustCollect[protocol.FileInfo](t)(db.AllNeededGlobalFiles(folderID, protocol.LocalDeviceID, config.PullOrderAlphabetic, 0, 0))
+	if len(names) != 0 {
+		t.Log(names)
+		t.Error("need no files")
+	}
+}
+
+func TestRemoveDontNeedLocalIgnored(t *testing.T) {
+	t.Parallel()
+
+	db, err := OpenTemp()
+	if err != nil {
+		t.Fatal(err)
+	}
+	t.Cleanup(func() {
+		if err := db.Close(); err != nil {
+			t.Fatal(err)
+		}
+	})
+
+	// A local ignored file
+	file := genFile("test1", 1, 103)
+	file.SetIgnored()
+	files := []protocol.FileInfo{file}
+	err = db.Update(folderID, protocol.LocalDeviceID, files)
+	if err != nil {
+		t.Fatal(err)
+	}
+
+	// Which the remote doesn't have (no update)
+
+	// They don't need it
+	s, err := db.CountNeed(folderID, protocol.DeviceID{42})
+	if err != nil {
+		t.Fatal(err)
+	}
+	if s.Bytes != 0 || s.Files != 0 {
+		t.Log(s)
+		t.Error("bad need")
+	}
+
+	// It shouldn't show up in their need list
+	names := mustCollect[protocol.FileInfo](t)(db.AllNeededGlobalFiles(folderID, protocol.DeviceID{42}, config.PullOrderAlphabetic, 0, 0))
+	if len(names) != 0 {
+		t.Log(names)
+		t.Error("need no files")
+	}
+}
+
+func TestLocalDontNeedDeletedMissing(t *testing.T) {
+	t.Parallel()
+
+	db, err := OpenTemp()
+	if err != nil {
+		t.Fatal(err)
+	}
+	t.Cleanup(func() {
+		if err := db.Close(); err != nil {
+			t.Fatal(err)
+		}
+	})
+
+	// A remote deleted file
+	file := genFile("test1", 1, 103)
+	file.SetDeleted(42)
+	files := []protocol.FileInfo{file}
+	err = db.Update(folderID, protocol.DeviceID{42}, files)
+	if err != nil {
+		t.Fatal(err)
+	}
+
+	// Which we don't have (no local update)
+
+	// We don't need it
+	s, err := db.CountNeed(folderID, protocol.LocalDeviceID)
+	if err != nil {
+		t.Fatal(err)
+	}
+	if s.Bytes != 0 || s.Files != 0 || s.Deleted != 0 {
+		t.Log(s)
+		t.Error("bad need")
+	}
+
+	// It shouldn't show up in the need list
+	names := mustCollect[protocol.FileInfo](t)(db.AllNeededGlobalFiles(folderID, protocol.LocalDeviceID, config.PullOrderAlphabetic, 0, 0))
+	if len(names) != 0 {
+		t.Log(names)
+		t.Error("need no files")
+	}
+}
+
+func TestRemoteDontNeedDeletedMissing(t *testing.T) {
+	t.Parallel()
+
+	db, err := OpenTemp()
+	if err != nil {
+		t.Fatal(err)
+	}
+	t.Cleanup(func() {
+		if err := db.Close(); err != nil {
+			t.Fatal(err)
+		}
+	})
+
+	// A local deleted file
+	file := genFile("test1", 1, 103)
+	file.SetDeleted(42)
+	files := []protocol.FileInfo{file}
+	err = db.Update(folderID, protocol.LocalDeviceID, files)
+	if err != nil {
+		t.Fatal(err)
+	}
+
+	// Which the remote doesn't have (no local update)
+
+	// They don't need it
+	s, err := db.CountNeed(folderID, protocol.DeviceID{42})
+	if err != nil {
+		t.Fatal(err)
+	}
+	if s.Bytes != 0 || s.Files != 0 || s.Deleted != 0 {
+		t.Log(s)
+		t.Error("bad need")
+	}
+
+	// It shouldn't show up in their need list
+	names := mustCollect[protocol.FileInfo](t)(db.AllNeededGlobalFiles(folderID, protocol.DeviceID{42}, config.PullOrderAlphabetic, 0, 0))
+	if len(names) != 0 {
+		t.Log(names)
+		t.Error("need no files")
+	}
+}
+
+func TestNeedRemoteSymlinkAndDir(t *testing.T) {
+	t.Parallel()
+
+	db, err := OpenTemp()
+	if err != nil {
+		t.Fatal(err)
+	}
+	t.Cleanup(func() {
+		if err := db.Close(); err != nil {
+			t.Fatal(err)
+		}
+	})
+
+	// Two remote "specials", a symlink and a directory
+	var v protocol.Vector
+	v.Update(1)
+	files := []protocol.FileInfo{
+		{Name: "sym", Type: protocol.FileInfoTypeSymlink, Sequence: 100, Version: v, Blocks: genBlocks("symlink", 0, 1)},
+		{Name: "dir", Type: protocol.FileInfoTypeDirectory, Sequence: 101, Version: v},
+	}
+	err = db.Update(folderID, protocol.DeviceID{42}, files)
+	if err != nil {
+		t.Fatal(err)
+	}
+
+	// We need them
+	s, err := db.CountNeed(folderID, protocol.LocalDeviceID)
+	if err != nil {
+		t.Fatal(err)
+	}
+	if s.Directories != 1 || s.Symlinks != 1 {
+		t.Log(s)
+		t.Error("bad need")
+	}
+
+	// They should be in the need list
+	names := mustCollect[protocol.FileInfo](t)(db.AllNeededGlobalFiles(folderID, protocol.LocalDeviceID, config.PullOrderAlphabetic, 0, 0))
+	if len(names) != 2 {
+		t.Log(names)
+		t.Error("bad need")
+	}
+}
+
+func TestNeedPagination(t *testing.T) {
+	t.Parallel()
+
+	db, err := OpenTemp()
+	if err != nil {
+		t.Fatal(err)
+	}
+	t.Cleanup(func() {
+		if err := db.Close(); err != nil {
+			t.Fatal(err)
+		}
+	})
+
+	// Several remote files
+	var v protocol.Vector
+	v.Update(1)
+	files := []protocol.FileInfo{
+		genFile("test0", 1, 100),
+		genFile("test1", 1, 101),
+		genFile("test2", 1, 102),
+		genFile("test3", 1, 103),
+		genFile("test4", 1, 104),
+		genFile("test5", 1, 105),
+		genFile("test6", 1, 106),
+		genFile("test7", 1, 107),
+		genFile("test8", 1, 108),
+		genFile("test9", 1, 109),
+	}
+	err = db.Update(folderID, protocol.DeviceID{42}, files)
+	if err != nil {
+		t.Fatal(err)
+	}
+
+	// We should get the first two
+	names := fiNames(mustCollect[protocol.FileInfo](t)(db.AllNeededGlobalFiles(folderID, protocol.LocalDeviceID, config.PullOrderAlphabetic, 2, 0)))
+	if !slices.Equal(names, []string{"test0", "test1"}) {
+		t.Log(names)
+		t.Error("bad need")
+	}
+
+	// We should get the next three
+	names = fiNames(mustCollect[protocol.FileInfo](t)(db.AllNeededGlobalFiles(folderID, protocol.LocalDeviceID, config.PullOrderAlphabetic, 3, 2)))
+	if !slices.Equal(names, []string{"test2", "test3", "test4"}) {
+		t.Log(names)
+		t.Error("bad need")
+	}
+
+	// We should get the last five
+	names = fiNames(mustCollect[protocol.FileInfo](t)(db.AllNeededGlobalFiles(folderID, protocol.LocalDeviceID, config.PullOrderAlphabetic, 5, 5)))
+	if !slices.Equal(names, []string{"test5", "test6", "test7", "test8", "test9"}) {
+		t.Log(names)
+		t.Error("bad need")
+	}
+}

internal/db/sqlite/db_indexid.go

@@ -0,0 +1,163 @@
+// Copyright (C) 2025 The Syncthing Authors.
+//
+// This Source Code Form is subject to the terms of the Mozilla Public
+// License, v. 2.0. If a copy of the MPL was not distributed with this file,
+// You can obtain one at https://mozilla.org/MPL/2.0/.
+
+package sqlite
+
+import (
+	"database/sql"
+	"encoding/hex"
+	"errors"
+	"fmt"
+
+	"github.com/syncthing/syncthing/internal/itererr"
+	"github.com/syncthing/syncthing/lib/protocol"
+)
+
+func (s *DB) GetIndexID(folder string, device protocol.DeviceID) (protocol.IndexID, error) {
+	// Try a fast read-only query to begin with. If it does not find the ID
+	// we'll do the full thing under a lock.
+	var indexID string
+	if err := s.stmt(`
+		SELECT i.index_id FROM indexids i
+		INNER JOIN folders o ON o.idx  = i.folder_idx
+		INNER JOIN devices d ON d.idx  = i.device_idx
+		WHERE o.folder_id = ? AND d.device_id = ?
+	`).Get(&indexID, folder, device.String()); err == nil && indexID != "" {
+		idx, err := indexIDFromHex(indexID)
+		return idx, wrap(err, "select")
+	}
+	if device != protocol.LocalDeviceID {
+		// For non-local devices we do not create the index ID, so return
+		// zero anyway if we don't have one.
+		return 0, nil
+	}
+
+	s.updateLock.Lock()
+	defer s.updateLock.Unlock()
+
+	// We are now operating only for the local device ID
+
+	folderIdx, err := s.folderIdxLocked(folder)
+	if err != nil {
+		return 0, wrap(err)
+	}
+
+	if err := s.stmt(`
+		SELECT index_id FROM indexids WHERE folder_idx = ? AND device_idx = {{.LocalDeviceIdx}}
+	`).Get(&indexID, folderIdx); err != nil && !errors.Is(err, sql.ErrNoRows) {
+		return 0, wrap(err, "select local")
+	}
+
+	if indexID == "" {
+		// Generate a new index ID. Some trickiness in the query as we need
+		// to find the max sequence of local files if there already exist
+		// any.
+		id := protocol.NewIndexID()
+		if _, err := s.stmt(`
+			INSERT INTO indexids (folder_idx, device_idx, index_id, sequence)
+				SELECT ?, {{.LocalDeviceIdx}}, ?, COALESCE(MAX(sequence), 0) FROM files
+				WHERE folder_idx = ? AND device_idx = {{.LocalDeviceIdx}}
+			ON CONFLICT DO UPDATE SET index_id = ?
+		`).Exec(folderIdx, indexIDToHex(id), folderIdx, indexIDToHex(id)); err != nil {
+			return 0, wrap(err, "insert")
+		}
+		return id, nil
+	}
+
+	return indexIDFromHex(indexID)
+}
+
+func (s *DB) SetIndexID(folder string, device protocol.DeviceID, id protocol.IndexID) error {
+	s.updateLock.Lock()
+	defer s.updateLock.Unlock()
+
+	folderIdx, err := s.folderIdxLocked(folder)
+	if err != nil {
+		return wrap(err, "folder idx")
+	}
+	deviceIdx, err := s.deviceIdxLocked(device)
+	if err != nil {
+		return wrap(err, "device idx")
+	}
+
+	if _, err := s.stmt(`
+		INSERT OR REPLACE INTO indexids (folder_idx, device_idx, index_id, sequence) values (?, ?, ?, 0)
+	`).Exec(folderIdx, deviceIdx, indexIDToHex(id)); err != nil {
+		return wrap(err, "insert")
+	}
+	return nil
+}
+
+func (s *DB) DropAllIndexIDs() error {
+	s.updateLock.Lock()
+	defer s.updateLock.Unlock()
+	_, err := s.stmt(`DELETE FROM indexids`).Exec()
+	return wrap(err)
+}
+
+func (s *DB) GetDeviceSequence(folder string, device protocol.DeviceID) (int64, error) {
+	var res sql.NullInt64
+	err := s.stmt(`
+		SELECT sequence FROM indexids i
+		INNER JOIN folders o ON o.idx = i.folder_idx
+		INNER JOIN devices d ON d.idx = i.device_idx
+		WHERE o.folder_id = ? AND d.device_id = ?
+	`).Get(&res, folder, device.String())
+	if errors.Is(err, sql.ErrNoRows) {
+		return 0, nil
+	}
+	if err != nil {
+		return 0, wrap(err)
+	}
+	if !res.Valid {
+		return 0, nil
+	}
+	return res.Int64, nil
+}
+
+func (s *DB) RemoteSequences(folder string) (map[protocol.DeviceID]int64, error) {
+	type row struct {
+		Device string
+		Seq    int64
+	}
+
+	it, errFn := iterStructs[row](s.stmt(`
+		SELECT d.device_id AS device, i.sequence AS seq FROM indexids i
+		INNER JOIN folders o ON o.idx = i.folder_idx
+		INNER JOIN devices d ON d.idx = i.device_idx
+		WHERE o.folder_id = ? AND i.device_idx != {{.LocalDeviceIdx}}
+	`).Queryx(folder))
+
+	res := make(map[protocol.DeviceID]int64)
+	for row, err := range itererr.Zip(it, errFn) {
+		if err != nil {
+			return nil, wrap(err)
+		}
+		dev, err := protocol.DeviceIDFromString(row.Device)
+		if err != nil {
+			return nil, wrap(err, "device ID")
+		}
+		res[dev] = row.Seq
+	}
+	return res, nil
+}
+
+func indexIDFromHex(s string) (protocol.IndexID, error) {
+	bs, err := hex.DecodeString(s)
+	if err != nil {
+		return 0, fmt.Errorf("indexIDFromHex: %q: %w", s, err)
+	}
+	var id protocol.IndexID
+	if err := id.Unmarshal(bs); err != nil {
+		return 0, fmt.Errorf("indexIDFromHex: %q: %w", s, err)
+	}
+	return id, nil
+}
+
+func indexIDToHex(i protocol.IndexID) string {
+	bs, _ := i.Marshal()
+	return hex.EncodeToString(bs)
+}

internal/db/sqlite/db_indexid_test.go

@@ -0,0 +1,81 @@
+// Copyright (C) 2025 The Syncthing Authors.
+//
+// This Source Code Form is subject to the terms of the Mozilla Public
+// License, v. 2.0. If a copy of the MPL was not distributed with this file,
+// You can obtain one at https://mozilla.org/MPL/2.0/.
+
+package sqlite
+
+import (
+	"testing"
+
+	"github.com/syncthing/syncthing/lib/protocol"
+)
+
+func TestIndexIDs(t *testing.T) {
+	t.Parallel()
+
+	db, err := OpenTemp()
+	if err != nil {
+		t.Fatal()
+	}
+	t.Cleanup(func() {
+		if err := db.Close(); err != nil {
+			t.Fatal(err)
+		}
+	})
+
+	t.Run("LocalDeviceID", func(t *testing.T) {
+		t.Parallel()
+
+		localID, err := db.GetIndexID("foo", protocol.LocalDeviceID)
+		if err != nil {
+			t.Fatal(err)
+		}
+		if localID == 0 {
+			t.Fatal("should have been generated")
+		}
+
+		again, err := db.GetIndexID("foo", protocol.LocalDeviceID)
+		if err != nil {
+			t.Fatal(err)
+		}
+		if again != localID {
+			t.Fatal("should get same again")
+		}
+
+		other, err := db.GetIndexID("bar", protocol.LocalDeviceID)
+		if err != nil {
+			t.Fatal(err)
+		}
+		if other == localID {
+			t.Fatal("should not get same for other folder")
+		}
+	})
+
+	t.Run("OtherDeviceID", func(t *testing.T) {
+		t.Parallel()
+
+		localID, err := db.GetIndexID("foo", protocol.DeviceID{42})
+		if err != nil {
+			t.Fatal(err)
+		}
+		if localID != 0 {
+			t.Fatal("should have been zero")
+		}
+
+		newID := protocol.NewIndexID()
+		if err := db.SetIndexID("foo", protocol.DeviceID{42}, newID); err != nil {
+			t.Fatal(err)
+		}
+
+		again, err := db.GetIndexID("foo", protocol.DeviceID{42})
+		if err != nil {
+			t.Fatal(err)
+		}
+		if again != newID {
+			t.Log(again, newID)
+			t.Fatal("should get the ID we set")
+		}
+	})
+}

internal/db/sqlite/db_kv.go

@@ -0,0 +1,78 @@
+// Copyright (C) 2025 The Syncthing Authors.
+//
+// This Source Code Form is subject to the terms of the Mozilla Public
+// License, v. 2.0. If a copy of the MPL was not distributed with this file,
+// You can obtain one at https://mozilla.org/MPL/2.0/.
+
+package sqlite
+
+import (
+	"iter"
+
+	"github.com/jmoiron/sqlx"
+	"github.com/syncthing/syncthing/internal/db"
+)
+
+func (s *DB) GetKV(key string) ([]byte, error) {
+	var val []byte
+	if err := s.stmt(`
+		SELECT value FROM kv
+		WHERE key = ?
+	`).Get(&val, key); err != nil {
+		return nil, wrap(err)
+	}
+	return val, nil
+}
+
+func (s *DB) PutKV(key string, val []byte) error {
+	s.updateLock.Lock()
+	defer s.updateLock.Unlock()
+	_, err := s.stmt(`
+		INSERT OR REPLACE INTO kv (key, value)
+		VALUES (?, ?)
+	`).Exec(key, val)
+	return wrap(err)
+}
+
+func (s *DB) DeleteKV(key string) error {
+	s.updateLock.Lock()
+	defer s.updateLock.Unlock()
+	_, err := s.stmt(`
+		DELETE FROM kv WHERE key = ?
+	`).Exec(key)
+	return wrap(err)
+}
+
+func (s *DB) PrefixKV(prefix string) (iter.Seq[db.KeyValue], func() error) {
+	var rows *sqlx.Rows
+	var err error
+	if prefix == "" {
+		rows, err = s.stmt(`SELECT key, value FROM kv`).Queryx()
+	} else {
+		end := prefixEnd(prefix)
+		rows, err = s.stmt(`
+			SELECT key, value FROM kv
+			WHERE key >= ? AND key < ?
+		`).Queryx(prefix, end)
+	}
+	if err != nil {
+		return func(_ func(db.KeyValue) bool) {}, func() error { return err }
+	}
+
+	return func(yield func(db.KeyValue) bool) {
+			defer rows.Close()
+			for rows.Next() {
+				var key string
+				var val []byte
+				if err = rows.Scan(&key, &val); err != nil {
+					return
+				}
+				if !yield(db.KeyValue{Key: key, Value: val}) {
+					return
+				}
+			}
+			err = rows.Err()
+		}, func() error {
+			return err
+		}
+}

internal/db/sqlite/db_local.go

@@ -0,0 +1,126 @@
+// Copyright (C) 2025 The Syncthing Authors.
+//
+// This Source Code Form is subject to the terms of the Mozilla Public
+// License, v. 2.0. If a copy of the MPL was not distributed with this file,
+// You can obtain one at https://mozilla.org/MPL/2.0/.
+
+package sqlite
+
+import (
+	"database/sql"
+	"errors"
+	"fmt"
+	"iter"
+
+	"github.com/syncthing/syncthing/internal/db"
+	"github.com/syncthing/syncthing/internal/itererr"
+	"github.com/syncthing/syncthing/lib/osutil"
+	"github.com/syncthing/syncthing/lib/protocol"
+)
+
+func (s *DB) GetDeviceFile(folder string, device protocol.DeviceID, file string) (protocol.FileInfo, bool, error) {
+	file = osutil.NormalizedFilename(file)
+
+	var ind indirectFI
+	err := s.stmt(`
+		SELECT fi.fiprotobuf, bl.blprotobuf FROM fileinfos fi
+		INNER JOIN files f on fi.sequence = f.sequence
+		LEFT JOIN blocklists bl ON bl.blocklist_hash = f.blocklist_hash
+		INNER JOIN devices d ON f.device_idx = d.idx
+		INNER JOIN folders o ON f.folder_idx = o.idx
+		WHERE o.folder_id = ? AND d.device_id = ? AND f.name = ?
+	`).Get(&ind, folder, device.String(), file)
+	if errors.Is(err, sql.ErrNoRows) {
+		return protocol.FileInfo{}, false, nil
+	}
+	if err != nil {
+		return protocol.FileInfo{}, false, wrap(err)
+	}
+	fi, err := ind.FileInfo()
+	if err != nil {
+		return protocol.FileInfo{}, false, wrap(err, "indirect")
+	}
+	return fi, true, nil
+}
+
+func (s *DB) AllLocalFiles(folder string, device protocol.DeviceID) (iter.Seq[protocol.FileInfo], func() error) {
+	it, errFn := iterStructs[indirectFI](s.stmt(`
+		SELECT fi.fiprotobuf, bl.blprotobuf FROM fileinfos fi
+		INNER JOIN files f on fi.sequence = f.sequence
+		LEFT JOIN blocklists bl ON bl.blocklist_hash = f.blocklist_hash
+		INNER JOIN folders o ON o.idx = f.folder_idx
+		INNER JOIN devices d ON d.idx = f.device_idx
+		WHERE o.folder_id = ? AND d.device_id = ?
+	`).Queryx(folder, device.String()))
+	return itererr.Map(it, errFn, indirectFI.FileInfo)
+}
+
+func (s *DB) AllLocalFilesBySequence(folder string, device protocol.DeviceID, startSeq int64, limit int) (iter.Seq[protocol.FileInfo], func() error) {
+	var limitStr string
+	if limit > 0 {
+		limitStr = fmt.Sprintf(" LIMIT %d", limit)
+	}
+	it, errFn := iterStructs[indirectFI](s.stmt(`
+		SELECT fi.fiprotobuf, bl.blprotobuf FROM fileinfos fi
+		INNER JOIN files f on fi.sequence = f.sequence
+		LEFT JOIN blocklists bl ON bl.blocklist_hash = f.blocklist_hash
+		INNER JOIN folders o ON o.idx = f.folder_idx
+		INNER JOIN devices d ON d.idx = f.device_idx
+		WHERE o.folder_id = ? AND d.device_id = ? AND f.sequence >= ?
+		ORDER BY f.sequence`+limitStr).Queryx(
+		folder, device.String(), startSeq))
+	return itererr.Map(it, errFn, indirectFI.FileInfo)
+}
+
+func (s *DB) AllLocalFilesWithPrefix(folder string, device protocol.DeviceID, prefix string) (iter.Seq[protocol.FileInfo], func() error) {
+	if prefix == "" {
+		return s.AllLocalFiles(folder, device)
+	}
+
+	prefix = osutil.NormalizedFilename(prefix)
+	end := prefixEnd(prefix)
+
+	it, errFn := iterStructs[indirectFI](s.sql.Queryx(`
+		SELECT fi.fiprotobuf, bl.blprotobuf FROM fileinfos fi
+		INNER JOIN files f on fi.sequence = f.sequence
+		LEFT JOIN blocklists bl ON bl.blocklist_hash = f.blocklist_hash
+		INNER JOIN folders o ON o.idx = f.folder_idx
+		INNER JOIN devices d ON d.idx = f.device_idx
+		WHERE o.folder_id = ? AND d.device_id = ? AND f.name >= ? AND f.name < ?
+	`, folder, device.String(), prefix, end))
+	return itererr.Map(it, errFn, indirectFI.FileInfo)
+}
+
+func (s *DB) AllLocalFilesWithBlocksHash(folder string, h []byte) (iter.Seq[db.FileMetadata], func() error) {
+	return iterStructs[db.FileMetadata](s.stmt(`
+		SELECT f.sequence, f.name, f.type, f.modified as modnanos, f.size, f.deleted, f.invalid, f.local_flags as localflags FROM files f
+		INNER JOIN folders o ON o.idx = f.folder_idx
+		WHERE o.folder_id = ? AND f.device_idx = {{.LocalDeviceIdx}} AND f.blocklist_hash = ?
+	`).Queryx(folder, h))
+}
+
+func (s *DB) AllLocalFilesWithBlocksHashAnyFolder(h []byte) (iter.Seq2[string, db.FileMetadata], func() error) {
+	type row struct {
+		FolderID string `db:"folder_id"`
+		db.FileMetadata
+	}
+	it, errFn := iterStructs[row](s.stmt(`
+		SELECT o.folder_id, f.sequence, f.name, f.type, f.modified as modnanos, f.size, f.deleted, f.invalid, f.local_flags as localflags FROM files f
+		INNER JOIN folders o ON o.idx = f.folder_idx
+		WHERE f.device_idx = {{.LocalDeviceIdx}} AND f.blocklist_hash = ?
+	`).Queryx(h))
+	return itererr.Map2(it, errFn, func(r row) (string, db.FileMetadata, error) {
+		return r.FolderID, r.FileMetadata, nil
+	})
+}
+
+func (s *DB) AllLocalBlocksWithHash(hash []byte) (iter.Seq[db.BlockMapEntry], func() error) {
+	// We involve the files table in this select because deletion of blocks
+	// & blocklists is deferred (garbage collected) while the files list is
+	// not. This filters out blocks that are in fact deleted.
+	return iterStructs[db.BlockMapEntry](s.stmt(`
+		SELECT f.blocklist_hash as blocklisthash, b.idx as blockindex, b.offset, b.size FROM files f
+		LEFT JOIN blocks b ON f.blocklist_hash = b.blocklist_hash
+		WHERE f.device_idx = {{.LocalDeviceIdx}} AND b.hash = ?
+	`).Queryx(hash))
+}

internal/db/sqlite/db_local_test.go

@@ -0,0 +1,202 @@
+// Copyright (C) 2025 The Syncthing Authors.
+//
+// This Source Code Form is subject to the terms of the Mozilla Public
+// License, v. 2.0. If a copy of the MPL was not distributed with this file,
+// You can obtain one at https://mozilla.org/MPL/2.0/.
+
+package sqlite
+
+import (
+	"testing"
+
+	"github.com/syncthing/syncthing/internal/db"
+	"github.com/syncthing/syncthing/internal/itererr"
+	"github.com/syncthing/syncthing/lib/protocol"
+)
+
+func TestBlocks(t *testing.T) {
+	t.Parallel()
+
+	db, err := OpenTemp()
+	if err != nil {
+		t.Fatal()
+	}
+	t.Cleanup(func() {
+		if err := db.Close(); err != nil {
+			t.Fatal(err)
+		}
+	})
+
+	files := []protocol.FileInfo{
+		{
+			Name: "file1",
+			Blocks: []protocol.BlockInfo{
+				{Hash: []byte{1, 2, 3}, Offset: 0, Size: 42},
+				{Hash: []byte{2, 3, 4}, Offset: 42, Size: 42},
+				{Hash: []byte{3, 4, 5}, Offset: 84, Size: 42},
+			},
+		},
+		{
+			Name: "file2",
+			Blocks: []protocol.BlockInfo{
+				{Hash: []byte{2, 3, 4}, Offset: 0, Size: 42},
+				{Hash: []byte{3, 4, 5}, Offset: 42, Size: 42},
+				{Hash: []byte{4, 5, 6}, Offset: 84, Size: 42},
+			},
+		},
+	}
+
+	if err := db.Update("test", protocol.LocalDeviceID, files); err != nil {
+		t.Fatal(err)
+	}
+
+	// Search for blocks
+
+	vals, err := itererr.Collect(db.AllLocalBlocksWithHash([]byte{1, 2, 3}))
+	if err != nil {
+		t.Fatal(err)
+	}
+	if len(vals) != 1 {
+		t.Log(vals)
+		t.Fatal("expected one hit")
+	} else if vals[0].BlockIndex != 0 || vals[0].Offset != 0 || vals[0].Size != 42 {
+		t.Log(vals[0])
+		t.Fatal("bad entry")
+	}
+
+	// Get FileInfos for those blocks
+
+	found := 0
+	it, errFn := db.AllLocalFilesWithBlocksHashAnyFolder(vals[0].BlocklistHash)
+	for folder, fileInfo := range it {
+		if folder != folderID {
+			t.Fatal("should be same folder")
+		}
+		if fileInfo.Name != "file1" {
+			t.Fatal("should be file1")
+		}
+		found++
+	}
+	if err := errFn(); err != nil {
+		t.Fatal(err)
+	}
+	if found != 1 {
+		t.Fatal("should find one file")
+	}
+
+	// Get the other blocks
+
+	vals, err = itererr.Collect(db.AllLocalBlocksWithHash([]byte{3, 4, 5}))
+	if err != nil {
+		t.Fatal(err)
+	}
+	if len(vals) != 2 {
+		t.Log(vals)
+		t.Fatal("expected two hits")
+	}
+	// if vals[0].Index != 2 || vals[0].Offset != 84 || vals[0].Size != 42 {
+	// 	t.Log(vals[0])
+	// 	t.Fatal("bad entry 1")
+	// }
+	// if vals[1].Index != 1 || vals[1].Offset != 42 || vals[1].Size != 42 {
+	// 	t.Log(vals[1])
+	// 	t.Fatal("bad entry 2")
+	// }
+}
+
+func TestBlocksDeleted(t *testing.T) {
+	t.Parallel()
+
+	sdb, err := OpenTemp()
+	if err != nil {
+		t.Fatal()
+	}
+	t.Cleanup(func() {
+		if err := sdb.Close(); err != nil {
+			t.Fatal(err)
+		}
+	})
+
+	// Insert a file
+	file := genFile("foo", 1, 0)
+	if err := sdb.Update(folderID, protocol.LocalDeviceID, []protocol.FileInfo{file}); err != nil {
+		t.Fatal()
+	}
+
+	// We should find one entry for the block hash
+	search := file.Blocks[0].Hash
+	es := mustCollect[db.BlockMapEntry](t)(sdb.AllLocalBlocksWithHash(search))
+	if len(es) != 1 {
+		t.Fatal("expected one hit")
+	}
+
+	// Update the file with a new block hash
+	file.Blocks = genBlocks("foo", 42, 1)
+	if err := sdb.Update(folderID, protocol.LocalDeviceID, []protocol.FileInfo{file}); err != nil {
+		t.Fatal()
+	}
+
+	// Searching for the old hash should yield no hits
+	if hits := mustCollect[db.BlockMapEntry](t)(sdb.AllLocalBlocksWithHash(search)); len(hits) != 0 {
+		t.Log(hits)
+		t.Error("expected no hits")
+	}
+
+	// Searching for the new hash should yield one hits
+	if hits := mustCollect[db.BlockMapEntry](t)(sdb.AllLocalBlocksWithHash(file.Blocks[0].Hash)); len(hits) != 1 {
+		t.Log(hits)
+		t.Error("expected one hit")
+	}
+}
+
+func TestRemoteSequence(t *testing.T) {
+	t.Parallel()
+
+	sdb, err := OpenTemp()
+	if err != nil {
+		t.Fatal()
+	}
+	t.Cleanup(func() {
+		if err := sdb.Close(); err != nil {
+			t.Fatal(err)
+		}
+	})
+
+	// Insert a local file
+	file := genFile("foo", 1, 0)
+	if err := sdb.Update(folderID, protocol.LocalDeviceID, []protocol.FileInfo{file}); err != nil {
+		t.Fatal()
+	}
+
+	// Insert several remote files
+	file = genFile("foo1", 1, 42)
+	if err := sdb.Update(folderID, protocol.DeviceID{42}, []protocol.FileInfo{file}); err != nil {
+		t.Fatal()
+	}
+	if err := sdb.Update(folderID, protocol.DeviceID{43}, []protocol.FileInfo{file}); err != nil {
+		t.Fatal()
+	}
+	file = genFile("foo2", 1, 43)
+	if err := sdb.Update(folderID, protocol.DeviceID{43}, []protocol.FileInfo{file}); err != nil {
+		t.Fatal()
+	}
+	if err := sdb.Update(folderID, protocol.DeviceID{44}, []protocol.FileInfo{file}); err != nil {
+		t.Fatal()
+	}
+	file = genFile("foo3", 1, 44)
+	if err := sdb.Update(folderID, protocol.DeviceID{44}, []protocol.FileInfo{file}); err != nil {
+		t.Fatal()
+	}
+
+	// Verify remote sequences
+	seqs, err := sdb.RemoteSequences(folderID)
+	if err != nil {
+		t.Fatal(err)
+	}
+	if len(seqs) != 3 || seqs[protocol.DeviceID{42}] != 42 ||
+		seqs[protocol.DeviceID{43}] != 43 ||
+		seqs[protocol.DeviceID{44}] != 44 {
+		t.Log(seqs)
+		t.Error("bad seqs")
+	}
+}

internal/db/sqlite/db_mtimes.go

@@ -0,0 +1,54 @@
+// Copyright (C) 2025 The Syncthing Authors.
+//
+// This Source Code Form is subject to the terms of the Mozilla Public
+// License, v. 2.0. If a copy of the MPL was not distributed with this file,
+// You can obtain one at https://mozilla.org/MPL/2.0/.
+
+package sqlite
+
+import (
+	"time"
+)
+
+func (s *DB) GetMtime(folder, name string) (ondisk, virtual time.Time) {
+	var res struct {
+		Ondisk  int64
+		Virtual int64
+	}
+	if err := s.stmt(`
+		SELECT m.ondisk, m.virtual FROM mtimes m
+		INNER JOIN folders o ON o.idx = m.folder_idx
+		WHERE o.folder_id = ? AND m.name = ?
+	`).Get(&res, folder, name); err != nil {
+		return time.Time{}, time.Time{}
+	}
+	return time.Unix(0, res.Ondisk), time.Unix(0, res.Virtual)
+}
+
+func (s *DB) PutMtime(folder, name string, ondisk, virtual time.Time) error {
+	s.updateLock.Lock()
+	defer s.updateLock.Unlock()
+	folderIdx, err := s.folderIdxLocked(folder)
+	if err != nil {
+		return wrap(err)
+	}
+	_, err = s.stmt(`
+		INSERT OR REPLACE INTO mtimes (folder_idx, name, ondisk, virtual)
+		VALUES (?, ?, ?, ?)
+	`).Exec(folderIdx, name, ondisk.UnixNano(), virtual.UnixNano())
+	return wrap(err)
+}
+
+func (s *DB) DeleteMtime(folder, name string) error {
+	s.updateLock.Lock()
+	defer s.updateLock.Unlock()
+	folderIdx, err := s.folderIdxLocked(folder)
+	if err != nil {
+		return wrap(err)
+	}
+	_, err = s.stmt(`
+		DELETE FROM mtimes
+		WHERE folder_idx = ? AND name = ?
+	`).Exec(folderIdx, name)
+	return wrap(err)
+}

internal/db/sqlite/db_mtimes_test.go

@@ -0,0 +1,54 @@
+// Copyright (C) 2025 The Syncthing Authors.
+//
+// This Source Code Form is subject to the terms of the Mozilla Public
+// License, v. 2.0. If a copy of the MPL was not distributed with this file,
+// You can obtain one at https://mozilla.org/MPL/2.0/.
+
+package sqlite
+
+import (
+	"testing"
+	"time"
+)
+
+func TestMtimePairs(t *testing.T) {
+	t.Parallel()
+
+	db, err := OpenTemp()
+	if err != nil {
+		t.Fatal()
+	}
+	t.Cleanup(func() {
+		if err := db.Close(); err != nil {
+			t.Fatal(err)
+		}
+	})
+
+	t0 := time.Now().Truncate(time.Second)
+	t1 := t0.Add(1234567890)
+
+	// Set a pair
+	if err := db.PutMtime("foo", "bar", t0, t1); err != nil {
+		t.Fatal(err)
+	}
+
+	// Check it
+	gt0, gt1 := db.GetMtime("foo", "bar")
+	if !gt0.Equal(t0) || !gt1.Equal(t1) {
+		t.Log(t0, gt0)
+		t.Log(t1, gt1)
+		t.Log("bad times")
+	}
+
+	// Delete it
+	if err := db.DeleteMtime("foo", "bar"); err != nil {
+		t.Fatal(err)
+	}
+
+	// Check it
+	gt0, gt1 = db.GetMtime("foo", "bar")
+	if !gt0.IsZero() || !gt1.IsZero() {
+		t.Log(gt0, gt1)
+		t.Log("bad times")
+	}
+}

internal/db/sqlite/db_open.go

@@ -0,0 +1,203 @@
+// Copyright (C) 2025 The Syncthing Authors.
+//
+// This Source Code Form is subject to the terms of the Mozilla Public
+// License, v. 2.0. If a copy of the MPL was not distributed with this file,
+// You can obtain one at https://mozilla.org/MPL/2.0/.
+
+package sqlite
+
+import (
+	"database/sql"
+	"os"
+	"path/filepath"
+	"strconv"
+	"strings"
+	"text/template"
+
+	"github.com/jmoiron/sqlx"
+	"github.com/syncthing/syncthing/lib/build"
+	"github.com/syncthing/syncthing/lib/protocol"
+)
+
+const maxDBConns = 128
+
+func Open(path string) (*DB, error) {
+	// Open the database with options to enable foreign keys and recursive
+	// triggers (needed for the delete+insert triggers on row replace).
+	sqlDB, err := sqlx.Open(dbDriver, "file:"+path+"?"+commonOptions)
+	if err != nil {
+		return nil, wrap(err)
+	}
+	sqlDB.SetMaxOpenConns(maxDBConns)
+	if _, err := sqlDB.Exec(`PRAGMA journal_mode = WAL`); err != nil {
+		return nil, wrap(err, "PRAGMA journal_mode")
+	}
+	if _, err := sqlDB.Exec(`PRAGMA optimize = 0x10002`); err != nil {
+		// https://www.sqlite.org/pragma.html#pragma_optimize
+		return nil, wrap(err, "PRAGMA optimize")
+	}
+	if _, err := sqlDB.Exec(`PRAGMA journal_size_limit = 6144000`); err != nil {
+		// https://www.powersync.com/blog/sqlite-optimizations-for-ultra-high-performance
+		return nil, wrap(err, "PRAGMA journal_size_limit")
+	}
+	return openCommon(sqlDB)
+}
+
+// Open the database with options suitable for the migration inserts. This
+// is not a safe mode of operation for normal processing, use only for bulk
+// inserts with a close afterwards.
+func OpenForMigration(path string) (*DB, error) {
+	sqlDB, err := sqlx.Open(dbDriver, "file:"+path+"?"+commonOptions)
+	if err != nil {
+		return nil, wrap(err, "open")
+	}
+	sqlDB.SetMaxOpenConns(1)
+	if _, err := sqlDB.Exec(`PRAGMA foreign_keys = 0`); err != nil {
+		return nil, wrap(err, "PRAGMA foreign_keys")
+	}
+	if _, err := sqlDB.Exec(`PRAGMA journal_mode = OFF`); err != nil {
+		return nil, wrap(err, "PRAGMA journal_mode")
+	}
+	if _, err := sqlDB.Exec(`PRAGMA synchronous = 0`); err != nil {
+		return nil, wrap(err, "PRAGMA synchronous")
+	}
+	return openCommon(sqlDB)
+}
+
+func OpenTemp() (*DB, error) {
+	// SQLite has a memory mode, but it works differently with concurrency
+	// compared to what we need with the WAL mode. So, no memory databases
+	// for now.
+	dir, err := os.MkdirTemp("", "syncthing-db")
+	if err != nil {
+		return nil, wrap(err)
+	}
+	path := filepath.Join(dir, "db")
+	l.Debugln("Test DB in", path)
+	return Open(path)
+}
+
+func openCommon(sqlDB *sqlx.DB) (*DB, error) {
+	if _, err := sqlDB.Exec(`PRAGMA auto_vacuum = INCREMENTAL`); err != nil {
+		return nil, wrap(err, "PRAGMA auto_vacuum")
+	}
+	if _, err := sqlDB.Exec(`PRAGMA default_temp_store = MEMORY`); err != nil {
+		return nil, wrap(err, "PRAGMA default_temp_store")
+	}
+	if _, err := sqlDB.Exec(`PRAGMA temp_store = MEMORY`); err != nil {
+		return nil, wrap(err, "PRAGMA temp_store")
+	}
+
+	db := &DB{
+		sql:        sqlDB,
+		statements: make(map[string]*sqlx.Stmt),
+	}
+
+	if err := db.runScripts("sql/schema/*"); err != nil {
+		return nil, wrap(err)
+	}
+
+	ver, _ := db.getAppliedSchemaVersion()
+	if ver.SchemaVersion > 0 {
+		filter := func(scr string) bool {
+			scr = filepath.Base(scr)
+			nstr, _, ok := strings.Cut(scr, "-")
+			if !ok {
+				return false
+			}
+			n, err := strconv.ParseInt(nstr, 10, 32)
+			if err != nil {
+				return false
+			}
+			return int(n) > ver.SchemaVersion
+		}
+		if err := db.runScripts("sql/migrations/*", filter); err != nil {
+			return nil, wrap(err)
+		}
+	}
+
+	// Touch device IDs that should always exist and have a low index
+	// numbers, and will never change
+	db.localDeviceIdx, _ = db.deviceIdxLocked(protocol.LocalDeviceID)
+
+	// Set the current schema version, if not already set
+	if err := db.setAppliedSchemaVersion(currentSchemaVersion); err != nil {
+		return nil, wrap(err)
+	}
+
+	db.tplInput = map[string]any{
+		"FlagLocalUnsupported": protocol.FlagLocalUnsupported,
+		"FlagLocalIgnored":     protocol.FlagLocalIgnored,
+		"FlagLocalMustRescan":  protocol.FlagLocalMustRescan,
+		"FlagLocalReceiveOnly": protocol.FlagLocalReceiveOnly,
+		"FlagLocalGlobal":      protocol.FlagLocalGlobal,
+		"FlagLocalNeeded":      protocol.FlagLocalNeeded,
+		"LocalDeviceIdx":       db.localDeviceIdx,
+		"SyncthingVersion":     build.LongVersion,
+	}
+
+	return db, nil
+}
+
+var tplFuncs = template.FuncMap{
+	"or": func(vs ...int) int {
+		v := vs[0]
+		for _, ov := range vs[1:] {
+			v |= ov
+		}
+		return v
+	},
+}
+
+// stmt returns a prepared statement for the given SQL string, after
+// applying local template expansions. The statement is cached.
+func (s *DB) stmt(tpl string) stmt {
+	tpl = strings.TrimSpace(tpl)
+
+	// Fast concurrent lookup of cached statement
+	s.statementsMut.RLock()
+	stmt, ok := s.statements[tpl]
+	s.statementsMut.RUnlock()
+	if ok {
+		return stmt
+	}
+
+	// On miss, take the full lock, check again
+	s.statementsMut.Lock()
+	defer s.statementsMut.Unlock()
+	stmt, ok = s.statements[tpl]
+	if ok {
+		return stmt
+	}
+
+	// Apply template expansions
+	var sb strings.Builder
+	compTpl := template.Must(template.New("tpl").Funcs(tplFuncs).Parse(tpl))
+	if err := compTpl.Execute(&sb, s.tplInput); err != nil {
+		panic("bug: bad template: " + err.Error())
+	}
+
+	// Prepare and cache
+	stmt, err := s.sql.Preparex(sb.String())
+	if err != nil {
+		return failedStmt{err}
+	}
+	s.statements[tpl] = stmt
+	return stmt
+}
+
+type stmt interface {
+	Exec(args ...any) (sql.Result, error)
+	Get(dest any, args ...any) error
+	Queryx(args ...any) (*sqlx.Rows, error)
+	Select(dest any, args ...any) error
+}
+
+type failedStmt struct {
+	err error
+}
+
+func (f failedStmt) Exec(_ ...any) (sql.Result, error)   { return nil, f.err }
+func (f failedStmt) Get(_ any, _ ...any) error           { return f.err }
+func (f failedStmt) Queryx(_ ...any) (*sqlx.Rows, error) { return nil, f.err }
+func (f failedStmt) Select(_ any, _ ...any) error        { return f.err }

internal/db/sqlite/db_open_cgo.go

@@ -0,0 +1,18 @@
+// Copyright (C) 2025 The Syncthing Authors.
+//
+// This Source Code Form is subject to the terms of the Mozilla Public
+// License, v. 2.0. If a copy of the MPL was not distributed with this file,
+// You can obtain one at https://mozilla.org/MPL/2.0/.
+
+//go:build cgo
+
+package sqlite
+
+import (
+	_ "github.com/mattn/go-sqlite3" // register sqlite3 database driver
+)
+
+const (
+	dbDriver      = "sqlite3"
+	commonOptions = "_fk=true&_rt=true&_cache_size=-65536&_sync=1&_txlock=immediate"
+)

internal/db/sqlite/db_open_nocgo.go

@@ -0,0 +1,23 @@
+// Copyright (C) 2025 The Syncthing Authors.
+//
+// This Source Code Form is subject to the terms of the Mozilla Public
+// License, v. 2.0. If a copy of the MPL was not distributed with this file,
+// You can obtain one at https://mozilla.org/MPL/2.0/.
+
+//go:build !cgo && !wazero
+
+package sqlite
+
+import (
+	"github.com/syncthing/syncthing/lib/build"
+	_ "modernc.org/sqlite" // register sqlite database driver
+)
+
+const (
+	dbDriver      = "sqlite"
+	commonOptions = "_pragma=foreign_keys(1)&_pragma=recursive_triggers(1)&_pragma=cache_size(-65536)&_pragma=synchronous(1)"
+)
+
+func init() {
+	build.AddTag("modernc-sqlite")
+}

internal/db/sqlite/db_prepared.go

@@ -0,0 +1,44 @@
+// Copyright (C) 2025 The Syncthing Authors.
+//
+// This Source Code Form is subject to the terms of the Mozilla Public
+// License, v. 2.0. If a copy of the MPL was not distributed with this file,
+// You can obtain one at https://mozilla.org/MPL/2.0/.
+
+package sqlite
+
+import "github.com/jmoiron/sqlx"
+
+type txPreparedStmts struct {
+	*sqlx.Tx
+	stmts map[string]*sqlx.Stmt
+}
+
+func (p *txPreparedStmts) Preparex(query string) (*sqlx.Stmt, error) {
+	if p.stmts == nil {
+		p.stmts = make(map[string]*sqlx.Stmt)
+	}
+	stmt, ok := p.stmts[query]
+	if ok {
+		return stmt, nil
+	}
+	stmt, err := p.Tx.Preparex(query)
+	if err != nil {
+		return nil, wrap(err)
+	}
+	p.stmts[query] = stmt
+	return stmt, nil
+}
+
+func (p *txPreparedStmts) Commit() error {
+	for _, s := range p.stmts {
+		s.Close()
+	}
+	return p.Tx.Commit()
+}
+
+func (p *txPreparedStmts) Rollback() error {
+	for _, s := range p.stmts {
+		s.Close()
+	}
+	return p.Tx.Rollback()
+}

internal/db/sqlite/db_schema.go

@@ -0,0 +1,88 @@
+// Copyright (C) 2025 The Syncthing Authors.
+//
+// This Source Code Form is subject to the terms of the Mozilla Public
+// License, v. 2.0. If a copy of the MPL was not distributed with this file,
+// You can obtain one at https://mozilla.org/MPL/2.0/.
+
+package sqlite
+
+import (
+	"embed"
+	"io/fs"
+	"strings"
+	"time"
+
+	"github.com/syncthing/syncthing/lib/build"
+)
+
+const currentSchemaVersion = 1
+
+//go:embed sql/**
+var embedded embed.FS
+
+func (s *DB) runScripts(glob string, filter ...func(s string) bool) error {
+	scripts, err := fs.Glob(embedded, glob)
+	if err != nil {
+		return wrap(err)
+	}
+
+	tx, err := s.sql.Begin()
+	if err != nil {
+		return wrap(err)
+	}
+	defer tx.Rollback() //nolint:errcheck
+
+nextScript:
+	for _, scr := range scripts {
+		for _, fn := range filter {
+			if !fn(scr) {
+				l.Debugln("Skipping script", scr)
+				continue nextScript
+			}
+		}
+		l.Debugln("Executing script", scr)
+		bs, err := fs.ReadFile(embedded, scr)
+		if err != nil {
+			return wrap(err, scr)
+		}
+		// SQLite requires one statement per exec, so we split the init
+		// files on lines containing only a semicolon and execute them
+		// separately. We require it on a separate line because there are
+		// also statement-internal semicolons in the triggers.
+		for _, stmt := range strings.Split(string(bs), "\n;") {
+			if _, err := tx.Exec(stmt); err != nil {
+				return wrap(err, stmt)
+			}
+		}
+	}
+
+	return wrap(tx.Commit())
+}
+
+type schemaVersion struct {
+	SchemaVersion    int
+	AppliedAt        int64
+	SyncthingVersion string
+}
+
+func (s *schemaVersion) AppliedTime() time.Time {
+	return time.Unix(0, s.AppliedAt)
+}
+
+func (s *DB) setAppliedSchemaVersion(ver int) error {
+	_, err := s.stmt(`
+		INSERT OR IGNORE INTO schemamigrations (schema_version, applied_at, syncthing_version)
+		VALUES (?, ?, ?)
+	`).Exec(ver, time.Now().UnixNano(), build.LongVersion)
+	return wrap(err)
+}
+
+func (s *DB) getAppliedSchemaVersion() (schemaVersion, error) {
+	var v schemaVersion
+	err := s.stmt(`
+		SELECT schema_version as schemaversion, applied_at as appliedat, syncthing_version as syncthingversion FROM schemamigrations
+		ORDER BY schema_version DESC
+		LIMIT 1
+	`).Get(&v)
+	return v, wrap(err)
+}

internal/db/sqlite/db_service.go

@@ -0,0 +1,141 @@
+// Copyright (C) 2025 The Syncthing Authors.
+//
+// This Source Code Form is subject to the terms of the Mozilla Public
+// License, v. 2.0. If a copy of the MPL was not distributed with this file,
+// You can obtain one at https://mozilla.org/MPL/2.0/.
+
+package sqlite
+
+import (
+	"context"
+	"time"
+
+	"github.com/syncthing/syncthing/internal/db"
+)
+
+const (
+	internalMetaPrefix = "dbsvc"
+	lastMaintKey       = "lastMaint"
+)
+
+type Service struct {
+	sdb                 *DB
+	maintenanceInterval time.Duration
+	internalMeta        *db.Typed
+}
+
+func newService(sdb *DB, maintenanceInterval time.Duration) *Service {
+	return &Service{
+		sdb:                 sdb,
+		maintenanceInterval: maintenanceInterval,
+		internalMeta:        db.NewTyped(sdb, internalMetaPrefix),
+	}
+}
+
+func (s *Service) Serve(ctx context.Context) error {
+	// Run periodic maintenance
+
+	// Figure out when we last ran maintenance and schedule accordingly. If
+	// it was never, do it now.
+	lastMaint, _, _ := s.internalMeta.Time(lastMaintKey)
+	nextMaint := lastMaint.Add(s.maintenanceInterval)
+	wait := time.Until(nextMaint)
+	if wait < 0 {
+		wait = time.Minute
+	}
+	l.Debugln("Next periodic run in", wait)
+
+	timer := time.NewTimer(wait)
+	for {
+		select {
+		case <-ctx.Done():
+			return ctx.Err()
+		case <-timer.C:
+		}
+
+		if err := s.periodic(ctx); err != nil {
+			return wrap(err)
+		}
+
+		timer.Reset(s.maintenanceInterval)
+		l.Debugln("Next periodic run in", s.maintenanceInterval)
+		_ = s.internalMeta.PutTime(lastMaintKey, time.Now())
+	}
+}
+
+func (s *Service) periodic(ctx context.Context) error {
+	t0 := time.Now()
+	l.Debugln("Periodic start")
+
+	s.sdb.updateLock.Lock()
+	defer s.sdb.updateLock.Unlock()
+
+	t1 := time.Now()
+	defer func() { l.Debugln("Periodic done in", time.Since(t1), "+", t1.Sub(t0)) }()
+
+	if err := s.garbageCollectBlocklistsAndBlocksLocked(ctx); err != nil {
+		return wrap(err)
+	}
+
+	_, _ = s.sdb.sql.ExecContext(ctx, `ANALYZE`)
+	_, _ = s.sdb.sql.ExecContext(ctx, `PRAGMA optimize`)
+	_, _ = s.sdb.sql.ExecContext(ctx, `PRAGMA incremental_vacuum`)
+	_, _ = s.sdb.sql.ExecContext(ctx, `PRAGMA wal_checkpoint(TRUNCATE)`)
+
+	return nil
+}
+
+func (s *Service) garbageCollectBlocklistsAndBlocksLocked(ctx context.Context) error {
+	// Remove all blocklists not referred to by any files and, by extension,
+	// any blocks not referred to by a blocklist. This is an expensive
+	// operation when run normally, especially if there are a lot of blocks
+	// to collect.
+	//
+	// We make this orders of magnitude faster by disabling foreign keys for
+	// the transaction and doing the cleanup manually. This requires using
+	// an explicit connection and disabling foreign keys before starting the
+	// transaction. We make sure to clean up on the way out.
+
+	conn, err := s.sdb.sql.Connx(ctx)
+	if err != nil {
+		return wrap(err)
+	}
+	defer conn.Close()
+
+	if _, err := conn.ExecContext(ctx, `PRAGMA foreign_keys = 0`); err != nil {
+		return wrap(err)
+	}
+	defer func() { //nolint:contextcheck
+		_, _ = conn.ExecContext(context.Background(), `PRAGMA foreign_keys = 1`)
+	}()
+
+	tx, err := conn.BeginTxx(ctx, nil)
+	if err != nil {
+		return wrap(err)
+	}
+	defer tx.Rollback() //nolint:errcheck
+
+	if res, err := tx.ExecContext(ctx, `
+		DELETE FROM blocklists
+		WHERE NOT EXISTS (
+			SELECT 1 FROM files WHERE files.blocklist_hash = blocklists.blocklist_hash
+		)`); err != nil {
+		return wrap(err, "delete blocklists")
+	} else if shouldDebug() {
+		rows, err := res.RowsAffected()
+		l.Debugln("Blocklist GC:", rows, err)
+	}
+
+	if res, err := tx.ExecContext(ctx, `
+		DELETE FROM blocks
+		WHERE NOT EXISTS (
+			SELECT 1 FROM blocklists WHERE blocklists.blocklist_hash = blocks.blocklist_hash
+		)`); err != nil {
+		return wrap(err, "delete blocks")
+	} else if shouldDebug() {
+		rows, err := res.RowsAffected()
+		l.Debugln("Blocks GC:", rows, err)
+	}
+
+	return wrap(tx.Commit())
+}

internal/db/sqlite/db_update.go

@@ -0,0 +1,549 @@
+// Copyright (C) 2025 The Syncthing Authors.
+//
+// This Source Code Form is subject to the terms of the Mozilla Public
+// License, v. 2.0. If a copy of the MPL was not distributed with this file,
+// You can obtain one at https://mozilla.org/MPL/2.0/.
+
+package sqlite
+
+import (
+	"cmp"
+	"context"
+	"fmt"
+	"runtime"
+	"slices"
+	"strings"
+
+	"github.com/jmoiron/sqlx"
+	"github.com/syncthing/syncthing/internal/gen/dbproto"
+	"github.com/syncthing/syncthing/internal/itererr"
+	"github.com/syncthing/syncthing/lib/osutil"
+	"github.com/syncthing/syncthing/lib/protocol"
+	"github.com/syncthing/syncthing/lib/sliceutil"
+	"google.golang.org/protobuf/proto"
+)
+
+func (s *DB) Update(folder string, device protocol.DeviceID, fs []protocol.FileInfo) error {
+	s.updateLock.Lock()
+	defer s.updateLock.Unlock()
+
+	folderIdx, err := s.folderIdxLocked(folder)
+	if err != nil {
+		return wrap(err)
+	}
+	deviceIdx, err := s.deviceIdxLocked(device)
+	if err != nil {
+		return wrap(err)
+	}
+
+	tx, err := s.sql.BeginTxx(context.Background(), nil)
+	if err != nil {
+		return wrap(err)
+	}
+	defer tx.Rollback() //nolint:errcheck
+	txp := &txPreparedStmts{Tx: tx}
+
+	//nolint:sqlclosecheck
+	insertFileStmt, err := txp.Preparex(`
+		INSERT OR REPLACE INTO files (folder_idx, device_idx, remote_sequence, name, type, modified, size, version, deleted, invalid, local_flags, blocklist_hash)
+		VALUES (?, ?, ?, ?, ?, ?, ?, ?, ?, ?, ?, ?)
+		RETURNING sequence
+	`)
+	if err != nil {
+		return wrap(err, "prepare insert file")
+	}
+
+	//nolint:sqlclosecheck
+	insertFileInfoStmt, err := txp.Preparex(`
+		INSERT INTO fileinfos (sequence, fiprotobuf)
+		VALUES (?, ?)
+	`)
+	if err != nil {
+		return wrap(err, "prepare insert fileinfo")
+	}
+
+	//nolint:sqlclosecheck
+	insertBlockListStmt, err := txp.Preparex(`
+		INSERT OR IGNORE INTO blocklists (blocklist_hash, blprotobuf)
+		VALUES (?, ?)
+	`)
+	if err != nil {
+		return wrap(err, "prepare insert blocklist")
+	}
+
+	var prevRemoteSeq int64
+	for i, f := range fs {
+		f.Name = osutil.NormalizedFilename(f.Name)
+
+		var blockshash *[]byte
+		if len(f.Blocks) > 0 {
+			f.BlocksHash = protocol.BlocksHash(f.Blocks)
+			blockshash = &f.BlocksHash
+		} else {
+			f.BlocksHash = nil
+		}
+
+		if f.Type == protocol.FileInfoTypeDirectory {
+			f.Size = 128 // synthetic directory size
+		}
+
+		// Insert the file.
+		//
+		// If it is a remote file, set remote_sequence otherwise leave it at
+		// null. Returns the new local sequence.
+		var remoteSeq *int64
+		if device != protocol.LocalDeviceID {
+			if i > 0 && f.Sequence == prevRemoteSeq {
+				return fmt.Errorf("duplicate remote sequence number %d", prevRemoteSeq)
+			}
+			prevRemoteSeq = f.Sequence
+			remoteSeq = &f.Sequence
+		}
+		var localSeq int64
+		if err := insertFileStmt.Get(&localSeq, folderIdx, deviceIdx, remoteSeq, f.Name, f.Type, f.ModTime().UnixNano(), f.Size, f.Version.String(), f.IsDeleted(), f.IsInvalid(), f.LocalFlags, blockshash); err != nil {
+			return wrap(err, "insert file")
+		}
+
+		if len(f.Blocks) > 0 {
+			// Indirect the block list
+			blocks := sliceutil.Map(f.Blocks, protocol.BlockInfo.ToWire)
+			bs, err := proto.Marshal(&dbproto.BlockList{Blocks: blocks})
+			if err != nil {
+				return wrap(err, "marshal blocklist")
+			}
+			if _, err := insertBlockListStmt.Exec(f.BlocksHash, bs); err != nil {
+				return wrap(err, "insert blocklist")
+			}
+
+			if device == protocol.LocalDeviceID {
+				// Insert all blocks
+				if err := s.insertBlocksLocked(txp, f.BlocksHash, f.Blocks); err != nil {
+					return wrap(err, "insert blocks")
+				}
+			}
+
+			f.Blocks = nil
+		}
+
+		// Insert the fileinfo
+		if device == protocol.LocalDeviceID {
+			f.Sequence = localSeq
+		}
+		bs, err := proto.Marshal(f.ToWire(true))
+		if err != nil {
+			return wrap(err, "marshal fileinfo")
+		}
+		if _, err := insertFileInfoStmt.Exec(localSeq, bs); err != nil {
+			return wrap(err, "insert fileinfo")
+		}
+
+		// Update global and need
+		if err := s.recalcGlobalForFile(txp, folderIdx, f.Name); err != nil {
+			return wrap(err)
+		}
+	}
+
+	return wrap(tx.Commit())
+}
+
+func (s *DB) DropFolder(folder string) error {
+	s.updateLock.Lock()
+	defer s.updateLock.Unlock()
+	_, err := s.stmt(`
+		DELETE FROM folders
+		WHERE folder_id = ?
+	`).Exec(folder)
+	return wrap(err)
+}
+
+func (s *DB) DropDevice(device protocol.DeviceID) error {
+	if device == protocol.LocalDeviceID {
+		panic("bug: cannot drop local device")
+	}
+
+	s.updateLock.Lock()
+	defer s.updateLock.Unlock()
+
+	deviceIdx, err := s.deviceIdxLocked(device)
+	if err != nil {
+		return wrap(err)
+	}
+
+	tx, err := s.sql.BeginTxx(context.Background(), nil)
+	if err != nil {
+		return wrap(err)
+	}
+	defer tx.Rollback() //nolint:errcheck
+	txp := &txPreparedStmts{Tx: tx}
+
+	// Find all folders where the device is involved
+	var folderIdxs []int64
+	if err := tx.Select(&folderIdxs, `
+		SELECT folder_idx
+		FROM counts
+		WHERE device_idx = ? AND count > 0
+		GROUP BY folder_idx
+	`, deviceIdx); err != nil {
+		return wrap(err)
+	}
+
+	// Drop the device, which cascades to delete all files etc for it
+	if _, err := tx.Exec(`DELETE FROM devices WHERE device_id = ?`, device.String()); err != nil {
+		return wrap(err)
+	}
+
+	// Recalc the globals for all affected folders
+	for _, idx := range folderIdxs {
+		if err := s.recalcGlobalForFolder(txp, idx); err != nil {
+			return wrap(err)
+		}
+	}
+
+	return wrap(tx.Commit())
+}
+
+func (s *DB) DropAllFiles(folder string, device protocol.DeviceID) error {
+	s.updateLock.Lock()
+	defer s.updateLock.Unlock()
+
+	// This is a two part operation, first dropping all the files and then
+	// recalculating the global state for the entire folder.
+
+	folderIdx, err := s.folderIdxLocked(folder)
+	if err != nil {
+		return wrap(err)
+	}
+	deviceIdx, err := s.deviceIdxLocked(device)
+	if err != nil {
+		return wrap(err)
+	}
+
+	tx, err := s.sql.BeginTxx(context.Background(), nil)
+	if err != nil {
+		return wrap(err)
+	}
+	defer tx.Rollback() //nolint:errcheck
+	txp := &txPreparedStmts{Tx: tx}
+
+	// Drop all the file entries
+
+	result, err := tx.Exec(`
+		DELETE FROM files
+		WHERE folder_idx = ? AND device_idx = ?
+	`, folderIdx, deviceIdx)
+	if err != nil {
+		return wrap(err)
+	}
+	if n, err := result.RowsAffected(); err == nil && n == 0 {
+		// The delete affected no rows, so we don't need to redo the entire
+		// global/need calculation.
+		return wrap(tx.Commit())
+	}
+
+	// Recalc global for the entire folder
+
+	if err := s.recalcGlobalForFolder(txp, folderIdx); err != nil {
+		return wrap(err)
+	}
+	return wrap(tx.Commit())
+}
+
+func (s *DB) DropFilesNamed(folder string, device protocol.DeviceID, names []string) error {
+	for i := range names {
+		names[i] = osutil.NormalizedFilename(names[i])
+	}
+
+	s.updateLock.Lock()
+	defer s.updateLock.Unlock()
+
+	folderIdx, err := s.folderIdxLocked(folder)
+	if err != nil {
+		return wrap(err)
+	}
+	deviceIdx, err := s.deviceIdxLocked(device)
+	if err != nil {
+		return wrap(err)
+	}
+
+	tx, err := s.sql.BeginTxx(context.Background(), nil)
+	if err != nil {
+		return wrap(err)
+	}
+	defer tx.Rollback() //nolint:errcheck
+	txp := &txPreparedStmts{Tx: tx}
+
+	// Drop the named files
+
+	query, args, err := sqlx.In(`
+		DELETE FROM files
+		WHERE folder_idx = ? AND device_idx = ? AND name IN (?)
+	`, folderIdx, deviceIdx, names)
+	if err != nil {
+		return wrap(err)
+	}
+	if _, err := tx.Exec(query, args...); err != nil {
+		return wrap(err)
+	}
+
+	// Recalc globals for the named files
+
+	for _, name := range names {
+		if err := s.recalcGlobalForFile(txp, folderIdx, name); err != nil {
+			return wrap(err)
+		}
+	}
+
+	return wrap(tx.Commit())
+}
+
+func (*DB) insertBlocksLocked(tx *txPreparedStmts, blocklistHash []byte, blocks []protocol.BlockInfo) error {
+	if len(blocks) == 0 {
+		return nil
+	}
+	bs := make([]map[string]any, len(blocks))
+	for i, b := range blocks {
+		bs[i] = map[string]any{
+			"hash":           b.Hash,
+			"blocklist_hash": blocklistHash,
+			"idx":            i,
+			"offset":         b.Offset,
+			"size":           b.Size,
+		}
+	}
+	_, err := tx.NamedExec(`
+		INSERT OR IGNORE INTO blocks (hash, blocklist_hash, idx, offset, size)
+		VALUES (:hash, :blocklist_hash, :idx, :offset, :size)
+	`, bs)
+	return wrap(err)
+}
+
+func (s *DB) recalcGlobalForFolder(txp *txPreparedStmts, folderIdx int64) error {
+	// Select files where there is no global, those are the ones we need to
+	// recalculate.
+	//nolint:sqlclosecheck
+	namesStmt, err := txp.Preparex(`
+		SELECT f.name FROM files f
+		WHERE f.folder_idx = ? AND NOT EXISTS (
+			SELECT 1 FROM files g
+			WHERE g.folder_idx = ? AND g.name = f.name AND g.local_flags & ? != 0
+		)
+		GROUP BY name
+	`)
+	if err != nil {
+		return wrap(err)
+	}
+	rows, err := namesStmt.Queryx(folderIdx, folderIdx, protocol.FlagLocalGlobal)
+	if err != nil {
+		return wrap(err)
+	}
+	defer rows.Close()
+	for rows.Next() {
+		var name string
+		if err := rows.Scan(&name); err != nil {
+			return wrap(err)
+		}
+		if err := s.recalcGlobalForFile(txp, folderIdx, name); err != nil {
+			return wrap(err)
+		}
+	}
+	return wrap(rows.Err())
+}
+
+func (s *DB) recalcGlobalForFile(txp *txPreparedStmts, folderIdx int64, file string) error {
+	//nolint:sqlclosecheck
+	selStmt, err := txp.Preparex(`
+		SELECT name, folder_idx, device_idx, sequence, modified, version, deleted, invalid, local_flags FROM files
+		WHERE folder_idx = ? AND name = ?
+	`)
+	if err != nil {
+		return wrap(err)
+	}
+	es, err := itererr.Collect(iterStructs[fileRow](selStmt.Queryx(folderIdx, file)))
+	if err != nil {
+		return wrap(err)
+	}
+	if len(es) == 0 {
+		// shouldn't happen
+		return nil
+	}
+
+	// Sort the entries; the global entry is at the head of the list
+	slices.SortFunc(es, fileRow.Compare)
+
+	// The global version is the first one in the list that is not invalid,
+	// or just the first one in the list if all are invalid.
+	var global fileRow
+	globIdx := slices.IndexFunc(es, func(e fileRow) bool { return !e.Invalid })
+	if globIdx < 0 {
+		globIdx = 0
+	}
+	global = es[globIdx]
+
+	// We "have" the file if the position in the list of versions is at the
+	// global version or better, or if the version is the same as the global
+	// file (we might be further down the list due to invalid flags), or if
+	// the global is deleted and we don't have it at all...
+	localIdx := slices.IndexFunc(es, func(e fileRow) bool { return e.DeviceIdx == s.localDeviceIdx })
+	hasLocal := localIdx >= 0 && localIdx <= globIdx || // have a better or equal version
+		localIdx >= 0 && es[localIdx].Version.Equal(global.Version.Vector) || // have an equal version but invalid/ignored
+		localIdx < 0 && global.Deleted // missing it, but the global is also deleted
+
+	// Set the global flag on the global entry. Set the need flag if the
+	// local device needs this file, unless it's invalid.
+	global.LocalFlags |= protocol.FlagLocalGlobal
+	if hasLocal || global.Invalid {
+		global.LocalFlags &= ^protocol.FlagLocalNeeded
+	} else {
+		global.LocalFlags |= protocol.FlagLocalNeeded
+	}
+	//nolint:sqlclosecheck
+	upStmt, err := txp.Prepare(`
+		UPDATE files SET local_flags = ?
+		WHERE folder_idx = ? AND device_idx = ? AND sequence = ?
+	`)
+	if err != nil {
+		return wrap(err)
+	}
+	if _, err := upStmt.Exec(global.LocalFlags, global.FolderIdx, global.DeviceIdx, global.Sequence); err != nil {
+		return wrap(err)
+	}
+
+	// Clear the need and global flags on all other entries
+	//nolint:sqlclosecheck
+	upStmt, err = txp.Prepare(`
+		UPDATE files SET local_flags = local_flags & ?
+		WHERE folder_idx = ? AND name = ? AND sequence != ? AND local_flags & ? != 0
+	`)
+	if err != nil {
+		return wrap(err)
+	}
+	if _, err := upStmt.Exec(^(protocol.FlagLocalNeeded | protocol.FlagLocalGlobal), folderIdx, global.Name, global.Sequence, protocol.FlagLocalNeeded|protocol.FlagLocalGlobal); err != nil {
+		return wrap(err)
+	}
+
+	return nil
+}
+
+func (s *DB) folderIdxLocked(folderID string) (int64, error) {
+	if _, err := s.stmt(`
+		INSERT OR IGNORE INTO folders(folder_id)
+		VALUES (?)
+	`).Exec(folderID); err != nil {
+		return 0, wrap(err)
+	}
+	var idx int64
+	if err := s.stmt(`
+		SELECT idx FROM folders
+		WHERE folder_id = ?
+	`).Get(&idx, folderID); err != nil {
+		return 0, wrap(err)
+	}
+
+	return idx, nil
+}
+
+func (s *DB) deviceIdxLocked(deviceID protocol.DeviceID) (int64, error) {
+	devStr := deviceID.String()
+	if _, err := s.stmt(`
+		INSERT OR IGNORE INTO devices(device_id)
+		VALUES (?)
+	`).Exec(devStr); err != nil {
+		return 0, wrap(err)
+	}
+	var idx int64
+	if err := s.stmt(`
+		SELECT idx FROM devices
+		WHERE device_id = ?
+	`).Get(&idx, devStr); err != nil {
+		return 0, wrap(err)
+	}
+
+	return idx, nil
+}
+
+// wrap returns the error wrapped with the calling function name and
+// optional extra context strings as prefix. A nil error wraps to nil.
+func wrap(err error, context ...string) error {
+	if err == nil {
+		return nil
+	}
+
+	prefix := "error"
+	pc, _, _, ok := runtime.Caller(1)
+	details := runtime.FuncForPC(pc)
+	if ok && details != nil {
+		prefix = strings.ToLower(details.Name())
+		if dotIdx := strings.LastIndex(prefix, "."); dotIdx > 0 {
+			prefix = prefix[dotIdx+1:]
+		}
+	}
+
+	if len(context) > 0 {
+		for i := range context {
+			context[i] = strings.TrimSpace(context[i])
+		}
+		extra := strings.Join(context, ", ")
+		return fmt.Errorf("%s (%s): %w", prefix, extra, err)
+	}
+
+	return fmt.Errorf("%s: %w", prefix, err)
+}
+
+type fileRow struct {
+	Name       string
+	Version    dbVector
+	FolderIdx  int64 `db:"folder_idx"`
+	DeviceIdx  int64 `db:"device_idx"`
+	Sequence   int64
+	Modified   int64
+	Size       int64
+	LocalFlags int64 `db:"local_flags"`
+	Deleted    bool
+	Invalid    bool
+}
+
+func (e fileRow) Compare(other fileRow) int {
+	// From FileInfo.WinsConflict
+	vc := e.Version.Vector.Compare(other.Version.Vector)
+	switch vc {
+	case protocol.Equal:
+		if e.Invalid != other.Invalid {
+			if e.Invalid {
+				return 1
+			}
+			return -1
+		}
+
+		// Compare the device ID index, lower is better. This is only
+		// deterministic to the extent that LocalDeviceID will always be the
+		// lowest one, order between remote devices is random (and
+		// irrelevant).
+		return cmp.Compare(e.DeviceIdx, other.DeviceIdx)
+	case protocol.Greater: // we are newer
+		return -1
+	case protocol.Lesser: // we are older
+		return 1
+	case protocol.ConcurrentGreater, protocol.ConcurrentLesser: // there is a conflict
+		if e.Invalid != other.Invalid {
+			if e.Invalid { // we are invalid, we lose
+				return 1
+			}
+			return -1 // they are invalid, we win
+		}
+		if e.Deleted != other.Deleted {
+			if e.Deleted { // we are deleted, we lose
+				return 1
+			}
+			return -1 // they are deleted, we win
+		}
+		if d := cmp.Compare(e.Modified, other.Modified); d != 0 {
+			return -d // positive d means we were newer, so we win (negative return)
+		}
+		if vc == protocol.ConcurrentGreater {
+			return -1 // we have a better device ID, we win
+		}
+		return 1 // they win
+	default:
+		return 0
+	}
+}

internal/db/sqlite/debug.go

@@ -0,0 +1,15 @@
+// Copyright (C) 2025 The Syncthing Authors.
+//
+// This Source Code Form is subject to the terms of the Mozilla Public
+// License, v. 2.0. If a copy of the MPL was not distributed with this file,
+// You can obtain one at https://mozilla.org/MPL/2.0/.
+
+package sqlite
+
+import (
+	"github.com/syncthing/syncthing/lib/logger"
+)
+
+var l = logger.DefaultLogger.NewFacility("sqlite", "SQLite database")
+
+func shouldDebug() bool { return l.ShouldDebug("sqlite") }

internal/db/sqlite/sql/README.md

@@ -0,0 +1,8 @@
+These SQL scripts are embedded in the binary.
+
+Scripts in `schema/` are run at every startup, in alphanumerical order.
+
+Scripts in `migrations/` are run when a migration is needed; the must begin
+with a number that equals the schema version that results from that
+migration. Migrations are not run on initial database creation, so the
+scripts in `schema/` should create the latest version.

internal/db/sqlite/sql/migrations/01-placeholder.sql

@@ -0,0 +1,7 @@
+-- Copyright (C) 2025 The Syncthing Authors.
+--
+-- This Source Code Form is subject to the terms of the Mozilla Public
+-- License, v. 2.0. If a copy of the MPL was not distributed with this file,
+-- You can obtain one at https://mozilla.org/MPL/2.0/.
+
+-- The next migration should be number two.

internal/db/sqlite/sql/schema/00-indexes.sql

@@ -0,0 +1,19 @@
+-- Copyright (C) 2025 The Syncthing Authors.
+--
+-- This Source Code Form is subject to the terms of the Mozilla Public
+-- License, v. 2.0. If a copy of the MPL was not distributed with this file,
+-- You can obtain one at https://mozilla.org/MPL/2.0/.
+
+-- folders map folder IDs as used by Syncthing to database folder indexes
+CREATE TABLE IF NOT EXISTS folders (
+    idx INTEGER NOT NULL PRIMARY KEY,
+    folder_id TEXT NOT NULL UNIQUE COLLATE BINARY
+) STRICT
+;
+
+-- devices map device IDs as used by Syncthing to database device indexes
+CREATE TABLE IF NOT EXISTS devices (
+    idx INTEGER NOT NULL PRIMARY KEY,
+    device_id TEXT NOT NULL UNIQUE COLLATE BINARY
+) STRICT
+;

internal/db/sqlite/sql/schema/10-schema.sql

@@ -0,0 +1,14 @@
+-- Copyright (C) 2025 The Syncthing Authors.
+--
+-- This Source Code Form is subject to the terms of the Mozilla Public
+-- License, v. 2.0. If a copy of the MPL was not distributed with this file,
+-- You can obtain one at https://mozilla.org/MPL/2.0/.
+
+-- Schema migrations hold the list of historical migrations applied
+CREATE TABLE IF NOT EXISTS schemamigrations (
+    schema_version INTEGER NOT NULL,
+    applied_at INTEGER NOT NULL, -- unix nanos
+    syncthing_version TEXT NOT NULL COLLATE BINARY,
+    PRIMARY KEY(schema_version)
+) STRICT
+;

internal/db/sqlite/sql/schema/20-files.sql

@@ -0,0 +1,62 @@
+-- Copyright (C) 2025 The Syncthing Authors.
+--
+-- This Source Code Form is subject to the terms of the Mozilla Public
+-- License, v. 2.0. If a copy of the MPL was not distributed with this file,
+-- You can obtain one at https://mozilla.org/MPL/2.0/.
+
+-- Files
+--
+-- The files table contains all files announced by any device. Files present
+-- on this device are filed under the LocalDeviceID, not the actual current
+-- device ID, for simplicity, consistency and portability. One announced
+-- version of each file is considered the "global" version - the latest one,
+-- that all other devices strive to replicate. This instance gets the Global
+-- flag bit set. There may be other identical instances of this file
+-- announced by other devices, but only one onstance gets the Global flag;
+-- this simplifies accounting. If the current device has the Global version,
+-- the LocalDeviceID instance of the file is the one that has the Global
+-- bit.
+--
+-- If the current device does not have that version of the file it gets the
+-- Need bit set. Only Global files announced by another device can have the
+-- Need bit. This allows for very efficient lookup of files needing handling
+-- on this device, which is a common query.
+CREATE TABLE IF NOT EXISTS files (
+    folder_idx INTEGER NOT NULL,
+    device_idx INTEGER NOT NULL, -- actual device ID or LocalDeviceID
+    sequence INTEGER NOT NULL PRIMARY KEY AUTOINCREMENT, -- our local database sequence, for each and every entry
+    remote_sequence INTEGER, -- remote device's sequence number, null for local or synthetic entries
+    name TEXT NOT NULL COLLATE BINARY,
+    type INTEGER NOT NULL, -- protocol.FileInfoType
+    modified INTEGER NOT NULL, -- Unix nanos
+    size INTEGER NOT NULL,
+    version TEXT NOT NULL COLLATE BINARY,
+    deleted INTEGER NOT NULL, -- boolean
+    invalid INTEGER NOT NULL, -- boolean
+    local_flags INTEGER NOT NULL,
+    blocklist_hash BLOB, -- null when there are no blocks
+    FOREIGN KEY(device_idx) REFERENCES devices(idx) ON DELETE CASCADE,
+    FOREIGN KEY(folder_idx) REFERENCES folders(idx) ON DELETE CASCADE
+) STRICT
+;
+-- FileInfos store the actual protobuf object. We do this separately to keep
+-- the files rows smaller and more efficient.
+CREATE TABLE IF NOT EXISTS fileinfos (
+    sequence INTEGER NOT NULL PRIMARY KEY, -- our local database sequence from the files table
+    fiprotobuf BLOB NOT NULL,
+    FOREIGN KEY(sequence) REFERENCES files(sequence) ON DELETE CASCADE DEFERRABLE INITIALLY DEFERRED
+) STRICT
+;
+-- There can be only one file per folder, device, and remote sequence number
+CREATE UNIQUE INDEX IF NOT EXISTS files_remote_sequence ON files (folder_idx, device_idx, remote_sequence)
+    WHERE remote_sequence IS NOT NULL
+;
+-- There can be only one file per folder, device, and name
+CREATE UNIQUE INDEX IF NOT EXISTS files_device_name ON files (folder_idx, device_idx, name)
+;
+-- We want to be able to look up & iterate files based on just folder and name
+CREATE INDEX IF NOT EXISTS files_name_only ON files (folder_idx, name)
+;
+-- We want to be able to look up & iterate files based on blocks hash
+CREATE INDEX IF NOT EXISTS files_blocklist_hash_only ON files (blocklist_hash, device_idx, folder_idx) WHERE blocklist_hash IS NOT NULL
+;

internal/db/sqlite/sql/schema/30-indexids.sql

@@ -0,0 +1,24 @@
+-- Copyright (C) 2025 The Syncthing Authors.
+--
+-- This Source Code Form is subject to the terms of the Mozilla Public
+-- License, v. 2.0. If a copy of the MPL was not distributed with this file,
+-- You can obtain one at https://mozilla.org/MPL/2.0/.
+
+-- indexids holds the index ID and maximum sequence for a given device and folder
+CREATE TABLE IF NOT EXISTS indexids (
+    device_idx INTEGER NOT NULL,
+    folder_idx INTEGER NOT NULL,
+    index_id TEXT NOT NULL COLLATE BINARY,
+    sequence INTEGER NOT NULL DEFAULT 0,
+    PRIMARY KEY(device_idx, folder_idx),
+    FOREIGN KEY(folder_idx) REFERENCES folders(idx) ON DELETE CASCADE,
+    FOREIGN KEY(device_idx) REFERENCES devices(idx) ON DELETE CASCADE
+) STRICT, WITHOUT ROWID
+;
+CREATE TRIGGER IF NOT EXISTS indexids_seq AFTER INSERT ON files
+BEGIN
+    INSERT INTO indexids (folder_idx, device_idx, index_id, sequence)
+        VALUES (NEW.folder_idx, NEW.device_idx, "", COALESCE(NEW.remote_sequence, NEW.sequence))
+        ON CONFLICT DO UPDATE SET sequence = COALESCE(NEW.remote_sequence, NEW.sequence);
+END
+;

internal/db/sqlite/sql/schema/40-counts.sql

@@ -0,0 +1,53 @@
+-- Copyright (C) 2025 The Syncthing Authors.
+--
+-- This Source Code Form is subject to the terms of the Mozilla Public
+-- License, v. 2.0. If a copy of the MPL was not distributed with this file,
+-- You can obtain one at https://mozilla.org/MPL/2.0/.
+
+-- Counts
+--
+-- Counts and sizes are maintained for each device, folder, type, flag bits
+-- combination.
+CREATE TABLE IF NOT EXISTS counts (
+    folder_idx INTEGER NOT NULL,
+    device_idx INTEGER NOT NULL,
+    type INTEGER NOT NULL,
+    local_flags INTEGER NOT NULL,
+    count INTEGER NOT NULL,
+    size INTEGER NOT NULL,
+    deleted INTEGER NOT NULL, -- boolean
+    PRIMARY KEY(folder_idx, device_idx, type, local_flags, deleted),
+    FOREIGN KEY(device_idx) REFERENCES devices(idx) ON DELETE CASCADE,
+    FOREIGN KEY(folder_idx) REFERENCES folders(idx) ON DELETE CASCADE
+) STRICT, WITHOUT ROWID
+;
+
+--- Maintain counts when files are added and removed using triggers
+
+CREATE TRIGGER IF NOT EXISTS counts_insert AFTER INSERT ON files
+BEGIN
+    INSERT INTO counts (folder_idx, device_idx, type, local_flags, count, size, deleted)
+        VALUES (NEW.folder_idx, NEW.device_idx, NEW.type, NEW.local_flags, 1, NEW.size, NEW.deleted)
+        ON CONFLICT DO UPDATE SET count = count + 1, size = size + NEW.size;
+END
+;
+CREATE TRIGGER IF NOT EXISTS counts_delete AFTER DELETE ON files
+BEGIN
+    UPDATE counts SET count = count - 1, size = size - OLD.size
+        WHERE folder_idx = OLD.folder_idx AND device_idx = OLD.device_idx AND type = OLD.type AND local_flags = OLD.local_flags AND deleted = OLD.deleted;
+END
+;
+CREATE TRIGGER IF NOT EXISTS counts_update AFTER UPDATE OF local_flags ON files
+WHEN NEW.local_flags != OLD.local_flags
+BEGIN
+    INSERT INTO counts (folder_idx, device_idx, type, local_flags, count, size, deleted)
+        VALUES (NEW.folder_idx, NEW.device_idx, NEW.type, NEW.local_flags, 1, NEW.size, NEW.deleted)
+        ON CONFLICT DO UPDATE SET count = count + 1, size = size + NEW.size;
+    UPDATE counts SET count = count - 1, size = size - OLD.size
+        WHERE folder_idx = OLD.folder_idx AND device_idx = OLD.device_idx AND type = OLD.type AND local_flags = OLD.local_flags AND deleted = OLD.deleted;
+END
+;
+DROP TRIGGER IF EXISTS counts_update_add -- tmp migration
+;
+DROP TRIGGER IF EXISTS counts_update_del -- tmp migration
+;

internal/db/sqlite/sql/schema/50-blocks.sql

@@ -0,0 +1,34 @@
+-- Copyright (C) 2025 The Syncthing Authors.
+--
+-- This Source Code Form is subject to the terms of the Mozilla Public
+-- License, v. 2.0. If a copy of the MPL was not distributed with this file,
+-- You can obtain one at https://mozilla.org/MPL/2.0/.
+
+-- Block lists
+--
+-- The block lists are extracted from FileInfos and stored separately. This
+-- reduces the database size by reusing the same block list entry for all
+-- devices announcing the same file. Doing it for all block lists instead of
+-- using a size cutoff simplifies queries. Block lists are garbage collected
+-- "manually", not using a trigger as that was too performance impacting.
+CREATE TABLE IF NOT EXISTS blocklists (
+    blocklist_hash BLOB NOT NULL PRIMARY KEY,
+    blprotobuf BLOB NOT NULL
+) STRICT
+;
+
+-- Blocks
+--
+-- For all local files we store the blocks individually for quick lookup. A
+-- given block can exist in multiple blocklists and at multiple offsets in a
+-- blocklist.
+CREATE TABLE IF NOT EXISTS blocks (
+    hash BLOB NOT NULL,
+    blocklist_hash BLOB NOT NULL,
+    idx INTEGER NOT NULL,
+    offset INTEGER NOT NULL,
+    size INTEGER NOT NULL,
+    PRIMARY KEY (hash, blocklist_hash, idx),
+    FOREIGN KEY(blocklist_hash) REFERENCES blocklists(blocklist_hash) ON DELETE CASCADE DEFERRABLE INITIALLY DEFERRED
+) STRICT
+;

internal/db/sqlite/sql/schema/50-mtimes.sql

@@ -0,0 +1,16 @@
+-- Copyright (C) 2025 The Syncthing Authors.
+--
+-- This Source Code Form is subject to the terms of the Mozilla Public
+-- License, v. 2.0. If a copy of the MPL was not distributed with this file,
+-- You can obtain one at https://mozilla.org/MPL/2.0/.
+
+--- Backing for the MtimeFS
+CREATE TABLE IF NOT EXISTS mtimes (
+    folder_idx INTEGER NOT NULL,
+    name TEXT NOT NULL,
+    ondisk INTEGER NOT NULL, -- unix nanos
+    virtual INTEGER NOT NULL, -- unix nanos
+    PRIMARY KEY(folder_idx, name),
+    FOREIGN KEY(folder_idx) REFERENCES folders(idx) ON DELETE CASCADE
+) STRICT, WITHOUT ROWID
+;

internal/db/sqlite/sql/schema/70-kv.sql

@@ -0,0 +1,13 @@
+-- Copyright (C) 2025 The Syncthing Authors.
+--
+-- This Source Code Form is subject to the terms of the Mozilla Public
+-- License, v. 2.0. If a copy of the MPL was not distributed with this file,
+-- You can obtain one at https://mozilla.org/MPL/2.0/.
+
+--- Simple KV store. This backs the "miscDB" we use for certain minor pieces
+--  of data.
+CREATE TABLE IF NOT EXISTS kv (
+    key TEXT NOT NULL PRIMARY KEY COLLATE BINARY,
+    value BLOB NOT NULL
+) STRICT
+;

internal/db/sqlite/util.go

@@ -0,0 +1,117 @@
+// Copyright (C) 2025 The Syncthing Authors.
+//
+// This Source Code Form is subject to the terms of the Mozilla Public
+// License, v. 2.0. If a copy of the MPL was not distributed with this file,
+// You can obtain one at https://mozilla.org/MPL/2.0/.
+
+package sqlite
+
+import (
+	"database/sql/driver"
+	"errors"
+	"iter"
+
+	"github.com/jmoiron/sqlx"
+	"github.com/syncthing/syncthing/internal/gen/bep"
+	"github.com/syncthing/syncthing/internal/gen/dbproto"
+	"github.com/syncthing/syncthing/lib/osutil"
+	"github.com/syncthing/syncthing/lib/protocol"
+	"google.golang.org/protobuf/proto"
+)
+
+// iterStructs returns an iterator over the given struct type by scanning
+// the SQL rows. `rows` is closed when the iterator exits.
+func iterStructs[T any](rows *sqlx.Rows, err error) (iter.Seq[T], func() error) {
+	if err != nil {
+		return func(_ func(T) bool) {}, func() error { return err }
+	}
+
+	var retErr error
+	return func(yield func(T) bool) {
+		defer rows.Close()
+		for rows.Next() {
+			v := new(T)
+			if err := rows.StructScan(v); err != nil {
+				retErr = err
+				break
+			}
+			if cleanuper, ok := any(v).(interface{ cleanup() }); ok {
+				cleanuper.cleanup()
+			}
+			if !yield(*v) {
+				return
+			}
+		}
+		if err := rows.Err(); err != nil && retErr == nil {
+			retErr = err
+		}
+	}, func() error { return retErr }
+}
+
+// dbVector is a wrapper that allows protocol.Vector values to be serialized
+// to and from the database.
+type dbVector struct { //nolint:recvcheck
+	protocol.Vector
+}
+
+func (v dbVector) Value() (driver.Value, error) {
+	return v.String(), nil
+}
+
+func (v *dbVector) Scan(value any) error {
+	str, ok := value.(string)
+	if !ok {
+		return errors.New("not a string")
+	}
+	if str == "" {
+		v.Vector = protocol.Vector{}
+		return nil
+	}
+	vec, err := protocol.VectorFromString(str)
+	if err != nil {
+		return wrap(err)
+	}
+	v.Vector = vec
+
+	return nil
+}
+
+// indirectFI constructs a FileInfo from separate marshalled FileInfo and
+// BlockList bytes.
+type indirectFI struct {
+	Name       string // not used, must be present as dest for Need iterator
+	FiProtobuf []byte
+	BlProtobuf []byte
+	Size       int64 // not used
+	Modified   int64 // not used
+}
+
+func (i indirectFI) FileInfo() (protocol.FileInfo, error) {
+	var fi bep.FileInfo
+	if err := proto.Unmarshal(i.FiProtobuf, &fi); err != nil {
+		return protocol.FileInfo{}, wrap(err, "unmarshal fileinfo")
+	}
+	if len(i.BlProtobuf) > 0 {
+		var bl dbproto.BlockList
+		if err := proto.Unmarshal(i.BlProtobuf, &bl); err != nil {
+			return protocol.FileInfo{}, wrap(err, "unmarshal blocklist")
+		}
+		fi.Blocks = bl.Blocks
+	}
+	fi.Name = osutil.NativeFilename(fi.Name)
+	return protocol.FileInfoFromDB(&fi), nil
+}
+
+func prefixEnd(s string) string {
+	if s == "" {
+		panic("bug: cannot represent end prefix for empty string")
+	}
+	bs := []byte(s)
+	for i := len(bs) - 1; i >= 0; i-- {
+		if bs[i] < 0xff {
+			bs[i]++
+			break
+		}
+	}
+	return string(bs)
+}