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perf(jobs): partial indexes for the enrich/maintenance scanners + boolean cleanup (E2 S6, PERF-17/18/3)

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Two scheduler jobs full-seq-scanned the 257k-row videos table every run:
- PERF-17 enrich_pending (`WHERE enriched_at IS NULL LIMIT N`, every few minutes):
  44,680 buffers even with 0 pending -> a partial ix_videos_enrich_pending makes
  it a 1-buffer index scan (empty when nothing pending).
- PERF-18 maintenance revalidate (`WHERE unavailable_since IS NULL ORDER BY
  last_checked_at NULLS FIRST LIMIT N`, ~300 pages/run): 44,754 buffers + top-N
  sort -> a partial ix_videos_recheck_order in that exact order = a 42-buffer
  index scan. The order_by is rewritten to `asc().nulls_first()` (equivalent to
  the old `(IS NULL) DESC, ASC`) so it rides the index; the unused plain
  ix_videos_last_checked_at is dropped.

PERF-3: drop the never-picked boolean btrees (is_short, via_explore) and slim the
useful ones to partials over the queried subset (via_search=true, NOT
shorts_probed, unavailable_since IS NOT NULL) — less write amplification on the
biggest table, same lookups. Model: those 6 columns lose their inline index=True
(the partials are migration-defined, like the search_vector GIN); live_status
left alone.

Measured on the prod-sized localdev reseed: enrich 44,680 -> 1 buffer (25.9 ->
0.02 ms), maintenance 44,754 -> 42 buffers (35.5 -> 0.17 ms); all 11 CONCURRENTLY
index ops on 257k rows in 0.75s. Gate green (346 pytest incl. drift + downgrade
round-trip).
This commit is contained in:
peter
2026-08-18 17:01:13 +02:00
parent 8b8b0ca5ab
commit 0ed4ac6958
3 changed files with 107 additions and 10 deletions
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backend/alembic/versions/0069_job_index_hygiene.py
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"""scheduler-job partial indexes + boolean-index cleanup (PERF-17/18/3)
Two scheduler jobs full-seq-scanned the 257k-row videos table every run:
- PERF-17: enrich_pending (`WHERE enriched_at IS NULL LIMIT N`, every few minutes) — 44.6k buffers /
run even when nothing is pending. A partial index over just the pending rows makes it a 1-buffer
(empty) index scan.
- PERF-18: maintenance revalidate (`WHERE unavailable_since IS NULL ORDER BY last_checked_at NULLS
FIRST LIMIT N`, ~300 pages/run) — 44.7k buffers/page; ix_videos_last_checked_at had idx_scan=0. A
partial index in that exact order serves it as an index scan (~36 buffers/page) and replaces the
unused plain one.
PERF-3: the videos table also carried plain btrees on low-cardinality boolean columns the planner never
picks (a `col IS false` majority predicate can't ride a btree). Drop the never-useful ones (is_short,
via_explore) and slim the rest to partial indexes over the small/shrinking subset the job queries target
(via_search=true, NOT shorts_probed, unavailable_since IS NOT NULL) — less write amplification on the
biggest table, same lookups. live_status is left alone (a separate finding).
All CONCURRENTLY (autocommit_block) — downtime ~0; IF (NOT) EXISTS keeps the drift test's
downgrade->re-upgrade idempotent.
"""
from typing import Sequence, Union
from alembic import op
revision: str = "0069_job_index_hygiene"
down_revision: Union[str, None] = "0068_published_at_not_null"
branch_labels: Union[str, Sequence[str], None] = None
depends_on: Union[str, Sequence[str], None] = None
def upgrade() -> None:
with op.get_context().autocommit_block():
# PERF-17: enrich-pending partial (empty when nothing is pending -> 1-buffer scan).
op.execute(
"CREATE INDEX CONCURRENTLY IF NOT EXISTS ix_videos_enrich_pending "
"ON videos (id) WHERE enriched_at IS NULL"
)
# PERF-18: maintenance revalidate order, as a partial in the exact WHERE + ORDER BY shape.
op.execute(
"CREATE INDEX CONCURRENTLY IF NOT EXISTS ix_videos_recheck_order "
"ON videos (last_checked_at ASC NULLS FIRST) WHERE unavailable_since IS NULL"
)
op.execute("DROP INDEX CONCURRENTLY IF EXISTS ix_videos_last_checked_at")
# PERF-3: drop the never-picked boolean btrees; slim the rest to partials over the target subset.
op.execute("DROP INDEX CONCURRENTLY IF EXISTS ix_videos_is_short")
op.execute("DROP INDEX CONCURRENTLY IF EXISTS ix_videos_via_explore")
op.execute("DROP INDEX CONCURRENTLY IF EXISTS ix_videos_via_search")
op.execute(
"CREATE INDEX CONCURRENTLY IF NOT EXISTS ix_videos_via_search "
"ON videos (id) WHERE via_search"
)
op.execute("DROP INDEX CONCURRENTLY IF EXISTS ix_videos_shorts_probed")
op.execute(
"CREATE INDEX CONCURRENTLY IF NOT EXISTS ix_videos_shorts_probed "
"ON videos (id) WHERE NOT shorts_probed"
)
op.execute("DROP INDEX CONCURRENTLY IF EXISTS ix_videos_unavailable_since")
op.execute(
"CREATE INDEX CONCURRENTLY IF NOT EXISTS ix_videos_unavailable_since "
"ON videos (unavailable_since) WHERE unavailable_since IS NOT NULL"
)
def downgrade() -> None:
with op.get_context().autocommit_block():
op.execute("DROP INDEX CONCURRENTLY IF EXISTS ix_videos_enrich_pending")
op.execute("DROP INDEX CONCURRENTLY IF EXISTS ix_videos_recheck_order")
op.execute(
"CREATE INDEX CONCURRENTLY IF NOT EXISTS ix_videos_last_checked_at "
"ON videos (last_checked_at)"
)
op.execute(
"CREATE INDEX CONCURRENTLY IF NOT EXISTS ix_videos_is_short ON videos (is_short)"
)
op.execute(
"CREATE INDEX CONCURRENTLY IF NOT EXISTS ix_videos_via_explore ON videos (via_explore)"
)
op.execute("DROP INDEX CONCURRENTLY IF EXISTS ix_videos_via_search")
op.execute(
"CREATE INDEX CONCURRENTLY IF NOT EXISTS ix_videos_via_search ON videos (via_search)"
)
op.execute("DROP INDEX CONCURRENTLY IF EXISTS ix_videos_shorts_probed")
op.execute(
"CREATE INDEX CONCURRENTLY IF NOT EXISTS ix_videos_shorts_probed ON videos (shorts_probed)"
)
op.execute("DROP INDEX CONCURRENTLY IF EXISTS ix_videos_unavailable_since")
op.execute(
"CREATE INDEX CONCURRENTLY IF NOT EXISTS ix_videos_unavailable_since "
"ON videos (unavailable_since)"
)