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Extend topic indexes for keyset pagination

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The "keyset"-style pagination that Tildes uses for topic listings uses
WHERE and ORDER BY clauses that involve multiple columns to keep a
deterministic ordering even when the values in the main sort column are
equal. For example, when sorting by number of votes, you're actually
ordering by num_votes DESC, topic_id DESC. The previous single-column
indexes were a little inefficient for this and couldn't always be used
well.

This commit extends all of the relevant indexes to composite ones that
contain topic_id as well, and drops all of the original ones. This
should be more efficient, and should probably be done to indexes on the
comments table as well.
This commit is contained in:
Deimos
2020-01-15 14:10:10 -07:00
parent 3830f31c0e
commit 47657c988e
2 changed files with 96 additions and 15 deletions
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76
tildes/alembic/versions/f4e1ef359307_extend_topic_indexes_for_keyset_.py Normal file
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@@ -0,0 +1,76 @@
"""Extend topic indexes for keyset pagination
Revision ID: f4e1ef359307
Revises: 4e101aae77cd
Create Date: 2020-01-15 20:52:23.380355
"""
from alembic import op
import sqlalchemy as sa
# revision identifiers, used by Alembic.
revision = "f4e1ef359307"
down_revision = "4e101aae77cd"
branch_labels = None
depends_on = None
def upgrade():
op.create_index(
"ix_topics_created_time_keyset",
"topics",
[sa.text("created_time DESC"), sa.text("topic_id DESC")],
unique=False,
)
op.create_index(
"ix_topics_last_activity_time_keyset",
"topics",
[sa.text("last_activity_time DESC"), sa.text("topic_id DESC")],
unique=False,
)
op.create_index(
"ix_topics_last_interesting_activity_time_keyset",
"topics",
[sa.text("last_interesting_activity_time DESC"), sa.text("topic_id DESC")],
unique=False,
)
op.create_index(
"ix_topics_num_comments_keyset",
"topics",
[sa.text("num_comments DESC"), sa.text("topic_id DESC")],
unique=False,
)
op.create_index(
"ix_topics_num_votes_keyset",
"topics",
[sa.text("num_votes DESC"), sa.text("topic_id DESC")],
unique=False,
)
op.drop_index("ix_topics_created_time", table_name="topics")
op.drop_index("ix_topics_last_activity_time", table_name="topics")
op.drop_index("ix_topics_last_interesting_activity_time", table_name="topics")
op.drop_index("ix_topics_num_comments", table_name="topics")
op.drop_index("ix_topics_num_votes", table_name="topics")
def downgrade():
op.create_index("ix_topics_num_votes", "topics", ["num_votes"], unique=False)
op.create_index("ix_topics_num_comments", "topics", ["num_comments"], unique=False)
op.create_index(
"ix_topics_last_interesting_activity_time",
"topics",
["last_interesting_activity_time"],
unique=False,
)
op.create_index(
"ix_topics_last_activity_time", "topics", ["last_activity_time"], unique=False
)
op.create_index("ix_topics_created_time", "topics", ["created_time"], unique=False)
op.drop_index("ix_topics_num_votes_keyset", table_name="topics")
op.drop_index("ix_topics_num_comments_keyset", table_name="topics")
op.drop_index(
"ix_topics_last_interesting_activity_time_keyset", table_name="topics"
)
op.drop_index("ix_topics_last_activity_time_keyset", table_name="topics")
op.drop_index("ix_topics_created_time_keyset", table_name="topics")

35
tildes/tildes/models/topic/topic.py
View File

@@ -23,7 +23,7 @@ from sqlalchemy import (
from sqlalchemy.dialects.postgresql import ENUM, JSONB, TSVECTOR
from sqlalchemy.ext.mutable import MutableDict
from sqlalchemy.orm import deferred, relationship
from sqlalchemy.sql.expression import text
from sqlalchemy.sql.expression import desc, text
from titlecase import titlecase
from tildes.enums import ContentMetadataFields, TopicContentType, TopicType
@@ -86,23 +86,14 @@ class Topic(DatabaseModel):
Integer, ForeignKey("topic_schedule.schedule_id"), index=True
)
created_time: datetime = Column(
TIMESTAMP(timezone=True),
nullable=False,
index=True,
server_default=text("NOW()"),
TIMESTAMP(timezone=True), nullable=False, server_default=text("NOW()"),
)
last_edited_time: Optional[datetime] = Column(TIMESTAMP(timezone=True))
last_activity_time: datetime = Column(
TIMESTAMP(timezone=True),
nullable=False,
index=True,
server_default=text("NOW()"),
TIMESTAMP(timezone=True), nullable=False, server_default=text("NOW()"),
)
last_interesting_activity_time: datetime = Column(
TIMESTAMP(timezone=True),
nullable=False,
index=True,
server_default=text("NOW()"),
TIMESTAMP(timezone=True), nullable=False, server_default=text("NOW()"),
)
is_deleted: bool = Column(
Boolean, nullable=False, server_default="false", index=True
@@ -125,8 +116,8 @@ class Topic(DatabaseModel):
content_metadata: Dict[str, Any] = Column(
MutableDict.as_mutable(JSONB(none_as_null=True))
)
num_comments: int = Column(Integer, nullable=False, server_default="0", index=True)
num_votes: int = Column(Integer, nullable=False, server_default="0", index=True)
num_comments: int = Column(Integer, nullable=False, server_default="0")
num_votes: int = Column(Integer, nullable=False, server_default="0")
_is_voting_closed: bool = Column(
"is_voting_closed", Boolean, nullable=False, server_default="false", index=True
)
@@ -142,6 +133,20 @@ class Topic(DatabaseModel):
__table_args__ = (
Index("ix_topics_tags_gist", tags, postgresql_using="gist"),
Index("ix_topics_search_tsv_gin", "search_tsv", postgresql_using="gin"),
# Indexes for keyset pagination
Index("ix_topics_created_time_keyset", desc(created_time), desc(topic_id)),
Index(
"ix_topics_last_activity_time_keyset",
desc(last_activity_time),
desc(topic_id),
),
Index(
"ix_topics_last_interesting_activity_time_keyset",
desc(last_interesting_activity_time),
desc(topic_id),
),
Index("ix_topics_num_comments_keyset", desc(num_comments), desc(topic_id)),
Index("ix_topics_num_votes_keyset", desc(num_votes), desc(topic_id)),
)
@hybrid_property # pylint: disable=used-before-assignment