perf: invalidate Redis tags concurrently instead of serially - #1262
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invalidate_by_tags() issued smembers+delete one tag at a time, so the caller's wall-clock latency grew linearly with tag count and stale entries stayed readable for the whole window. Fan the per-tag work out with asyncio.gather, reusing the per-layer tag-write semaphore already introduced for set() so the combined fan-out cannot exhaust the shared connection pool. One permit covers both commands for a tag since the delete depends on the smembers result. Closes #1261. Co-authored-by: Copilot App <223556219+Copilot@users.noreply.github.com>
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📝 WalkthroughSummary by CodeRabbit
Walkthrough
ChangesRedis tag invalidation
Estimated code review effort: 3 (Moderate) | ~20 minutes Possibly related issues
Possibly related PRs
Poem
🚥 Pre-merge checks | ✅ 6 | ❌ 1❌ Failed checks (1 warning)
✅ Passed checks (6 passed)
✨ Finishing Touches 💡 1🛠️ Fix failing CI checks 💡
📝 Generate docstrings
🧪 Generate unit tests (beta)
✨ Simplify code
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@linear-code @coderabbitai review Adversarial review requested. Four things I want challenged specifically, because they are the places I think this change is most likely to be wrong:
Also flagged in the body: this PR and open PR #1179 edit the same docstring and will conflict on merge. The resolution table is in the "Overlap with open PR #1179" section. |
Dependency Review✅ No vulnerabilities or license issues or OpenSSF Scorecard issues found.Snapshot WarningsEnsure that dependencies are being submitted on PR branches and consider enabling retry-on-snapshot-warnings. See the documentation for more information and troubleshooting advice. Scanned FilesNone |
Agent Completion Truth Gate: NOT_APPLICABLEEvidence agrees. Machine-readable verdict{
"details": {},
"reasons": [],
"verdict": "not_applicable"
} |
🧩 Analysis chain🏁 Script executed: #!/bin/bash
set -euo pipefail
printf '%s\n' '--- PR diff ---'
gh pr diff 1262 --repo groupthinking/EventRelay -- \
src/youtube_extension/backend/services/intelligent_cache.py \
tests/unit/test_intelligent_cache.py
printf '%s\n' '--- Source outline ---'
ast-grep outline src/youtube_extension/backend/services/intelligent_cache.py \
--items all --type class,function --match 'RedisCacheLayer|invalidate_by_tags|_get_tag_write_semaphore|set|_resolve_tag_write_limit' \
--view expanded
printf '%s\n' '--- Test outline ---'
ast-grep outline tests/unit/test_intelligent_cache.py \
--items all --type class,function --match 'TestRedisCacheLayerInvalidateByTags|test_invalidate' \
--view expanded
printf '%s\n' '--- Relevant source locations ---'
rg -n -C 8 \
'async def (invalidate_by_tags|set|_get_tag_write_semaphore|_resolve_tag_write_limit)\b|class RedisCacheLayer\b' \
src/youtube_extension/backend/services/intelligent_cache.py
printf '%s\n' '--- Relevant test locations ---'
rg -n -C 5 \
'class TestRedisCacheLayerInvalidateByTags\b|async def test_invalidate' \
tests/unit/test_intelligent_cache.py
printf '%s\n' '--- PR `#1179` overlap diff ---'
gh pr diff 1179 --repo groupthinking/EventRelay -- \
src/youtube_extension/backend/services/intelligent_cache.pyLength of output: 1647 🏁 Script executed: #!/bin/bash
set -euo pipefail
printf '%s\n' '--- Current PR changed files and base ---'
gh pr view 1262 --repo groupthinking/EventRelay \
--json baseRefName,headRefName,files \
--jq '.baseRefName, .headRefName, (.files[] | .path)'
printf '%s\n' '--- Scoped diff against merge base ---'
base_ref=$(gh pr view 1262 --repo groupthinking/EventRelay --json baseRefName --jq '.baseRefName')
merge_base=$(git merge-base "origin/${base_ref}" HEAD)
git diff --unified=80 "$merge_base" -- \
src/youtube_extension/backend/services/intelligent_cache.py \
tests/unit/test_intelligent_cache.py
printf '%s\n' '--- Source outline ---'
ast-grep outline src/youtube_extension/backend/services/intelligent_cache.py \
--items all --type class,function \
--match 'RedisCacheLayer|invalidate_by_tags|_get_tag_write_semaphore|_resolve_tag_write_limit|set' \
--view expanded || true
printf '%s\n' '--- Relevant source implementations ---'
rg -n -C 12 \
'async def (invalidate_by_tags|set)\b|def (_get_tag_write_semaphore|_resolve_tag_write_limit)\b|class RedisCacheLayer\b' \
src/youtube_extension/backend/services/intelligent_cache.py
printf '%s\n' '--- Relevant test implementations ---'
rg -n -C 8 \
'class TestRedisCacheLayerInvalidateByTags\b|async def test_invalidate' \
tests/unit/test_intelligent_cache.py
printf '%s\n' '--- PR `#1179` files and docstring patch ---'
gh pr view 1179 --repo groupthinking/EventRelay --json files --jq '.files[] | .path'
gh api "repos/groupthinking/EventRelay/pulls/1179/files?per_page=100" \
--jq '.[] | select(.filename == "src/youtube_extension/backend/services/intelligent_cache.py") | .patch'Length of output: 39043 🏁 Script executed: #!/bin/bash
set -euo pipefail
test_file=$(fd -t f '^test_intelligent_cache\.py$' | head -n 1)
if [ -z "$test_file" ]; then
echo 'test_intelligent_cache.py was not found'
exit 1
fi
printf '%s\n' '--- Complete RedisCacheLayer.set and invalidate_by_tags implementations ---'
sed -n '394,565p' src/youtube_extension/backend/services/intelligent_cache.py
printf '%s\n' '--- Test file and helpers ---'
printf 'Test file: %s\n' "$test_file"
rg -n -C 8 \
'^def (_make_redis_conn|_make_pool|_patch_redis)\b|^class TestRedisCacheLayerInvalidateByTags\b|async def test_invalidate' \
"$test_file"
printf '%s\n' '--- Test imports and surrounding invalidate test class ---'
sed -n '1,100p' "$test_file"
start=$(rg -n '^class TestRedisCacheLayerInvalidateByTags\b' "$test_file" | cut -d: -f1)
sed -n "${start},$((start+270))p" "$test_file"
printf '%s\n' '--- Declared redis dependency ---'
rg -n -C 3 'redis([<>=!~ ].*)?$|redis-py|redis\s*=' \
pyproject.toml requirements.txt requirements/*.txt setup.py setup.cfg 2>/dev/null || true
printf '%s\n' '--- asyncio.gather cancellation implementation ---'
python - <<'PY'
import asyncio
import inspect
print(inspect.getsource(asyncio.gather))
PY
printf '%s\n' '--- PR `#1179` target file patch ---'
gh api "repos/groupthinking/EventRelay/pulls/1179/files?per_page=100" \
--jq '.[] | select(.filename == "src/youtube_extension/backend/services/intelligent_cache.py") | .patch // "No patch returned"'Length of output: 1793 🏁 Script executed: #!/bin/bash
set -euo pipefail
printf '%s\n' '--- Complete RedisCacheLayer.set and invalidate_by_tags implementations ---'
sed -n '394,565p' src/youtube_extension/backend/services/intelligent_cache.py
printf '%s\n' '--- Repository locations that reference redis dependency metadata ---'
fd -t f -a '^(pyproject\.toml|requirements.*\.txt|setup\.py|setup\.cfg|Pipfile(\.lock)?)$' . \
-x sh -c 'echo "--- $1"; rg -n -C 3 "redis|hiredis" "$1" || true' sh {}
printf '%s\n' '--- asyncio.gather cancellation implementation ---'
python - <<'PY'
import asyncio
import inspect
print(inspect.getsource(asyncio.gather))
PY
printf '%s\n' '--- PR `#1179` target file patch ---'
gh api "repos/groupthinking/EventRelay/pulls/1179/files?per_page=100" \
--jq '.[] | select(.filename == "src/youtube_extension/backend/services/intelligent_cache.py") | .patch // "No patch returned"'
printf '%s\n' '--- Redis use and pool ownership in source ---'
rg -n -C 4 \
'redis\.Redis\(|ConnectionPool\.from_url|aclose\(|close\(' \
src/youtube_extension/backend/services/intelligent_cache.pyLength of output: 28930
The current scope is valid if the intended policy is “at most The other three claims hold:
The merge-conflict resolution for ✅ Action performedReview finished.
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There was a problem hiding this comment.
🟢 Ready to approve
The implementation satisfies the stated contract with comprehensive focused regression coverage.
This review doesn't count toward merge requirements. Sign up for the private preview to control whether Copilot approvals count.
Pull request overview
Concurrently invalidates Redis cache tags while sharing the existing connection-pool concurrency budget.
Changes:
- Adds bounded concurrent per-tag invalidation.
- Preserves failure and return-value behavior.
- Adds focused concurrency, ordering, and failure tests.
File summaries
| File | Description |
|---|---|
src/youtube_extension/backend/services/intelligent_cache.py |
Implements bounded concurrent invalidation and updates limiter documentation. |
tests/unit/test_intelligent_cache.py |
Tests concurrency limits, permit sharing, ordering, and task draining. |
Review details
- Files reviewed: 2/2 changed files
- Comments generated: 0
- Review effort level: Balanced
We're testing this review assessment. Please use 👍 or 👎 to tell us if it's correct.
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Review (automated remediation run) — verified, no blocking findings. CodeRabbit's status on this head is
CI is green on this head, including Merge note: ready to merge, but I'm not auto-merging — base is protected Generated by Claude Code |
CodeRabbit's adversarial review of #1262 found the permit-scope comment factually wrong: it claimed holding one permit across the smembers/delete pair keeps concurrently-held pool connections at the permit count "instead of twice it". redis.asyncio checks a connection out only for each command and returns it to the pool between the two awaits, so acquiring the permit per command would cap in-flight commands at the same limit. The real reason to hold across the pair is scheduling determinism and avoiding permit churn, not preventing a doubling of held connections. - Rewrite the inline comment in invalidate_by_tags() to state the true policy. - Fix the matching docstring of test_invalidate_holds_one_permit_across_both_commands. - Add test_invalidate_starts_no_command_after_context_exit_on_cancel, the cancellation regression guard CodeRabbit asked for: cancel mid-smembers and assert no Redis command starts after the connection context manager exits. No behaviour change; scheduling and return values are untouched. 163 passed. Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com> Claude-Session: https://claude.ai/code/session_01RJP3fieq6JJdEAZXQsJ3J6
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@coderabbitai review Addressed your one substantive finding in Permit-scope rationale (the false claim). You're right: Cancellation test. Added No behaviour change — scheduling, keys, return values, and the Your other three verdicts (cancellation parity, failure-path safety, non-vacuity of the three prove-fail tests) and the #1179 merge-conflict resolution are taken as-is. Generated by Claude Code |
🧩 Analysis chain🏁 Script executed: #!/bin/bash
set -euo pipefail
printf '%s\n' '--- Commit diff: 0cbf849 ---'
git show --format=fuller --find-renames --find-copies --unified=80 0cbf849 -- \
src/youtube_extension/backend/services/intelligent_cache.py \
tests/unit/test_intelligent_cache.py
printf '%s\n' '--- RedisCacheLayer source map ---'
ast-grep outline src/youtube_extension/backend/services/intelligent_cache.py \
--items all --type class,function \
--match 'RedisCacheLayer|invalidate_by_tags|_get_tag_write_semaphore|set' \
--view expanded || true
printf '%s\n' '--- Source implementations ---'
rg -n -C 16 \
'async def (invalidate_by_tags|set)\b|def _get_tag_write_semaphore\b|class RedisCacheLayer\b' \
src/youtube_extension/backend/services/intelligent_cache.py
printf '%s\n' '--- Invalidate test class map ---'
ast-grep outline tests/unit/test_intelligent_cache.py \
--items all --type class,function \
--match 'TestRedisCacheLayerInvalidateByTags|test_invalidate_holds_one_permit_across_both_commands|test_invalidate_starts_no_command_after_context_exit_on_cancel' \
--view expanded || true
printf '%s\n' '--- Revised and cancellation tests ---'
rg -n -C 25 \
'test_invalidate_holds_one_permit_across_both_commands|test_invalidate_starts_no_command_after_context_exit_on_cancel' \
tests/unit/test_intelligent_cache.pyLength of output: 32757 🏁 Script executed: #!/bin/bash
set -euo pipefail
test_file=$(fd -t f -a '^test_intelligent_cache\.py$' . | head -n 1)
if [ -z "$test_file" ]; then
echo 'ERROR: test_intelligent_cache.py was not found'
exit 1
fi
printf '--- Test file: %s ---\n' "$test_file"
printf '%s\n' '--- Mock helpers and Redis patching ---'
rg -n -C 30 \
'^def (_make_redis_conn|_patch_redis|_make_pool)\b|^class TestRedisCacheLayerInvalidateByTags\b' \
"$test_file"
printf '%s\n' '--- Changed tests ---'
rg -n -C 35 \
'async def test_invalidate_(holds_one_permit_across_both_commands|starts_no_command_after_context_exit_on_cancel)\b' \
"$test_file"
printf '%s\n' '--- Direct context manager use in target source ---'
sed -n '506,565p' src/youtube_extension/backend/services/intelligent_cache.py
printf '%s\n' '--- Python asyncio.gather cancellation implementation ---'
python - <<'PY'
import asyncio
import inspect
print(inspect.getsource(asyncio.gather))
PYLength of output: 1285 🏁 Script executed: #!/bin/bash
set -euo pipefail
test_path='tests/unit/test_intelligent_cache.py'
printf '%s\n' '--- Test path in commit ---'
git cat-file -e "0cbf849:${test_path}"
git ls-tree -r --name-only 0cbf849 -- "$test_path"
printf '%s\n' '--- Mock helpers and invalidate test class from commit ---'
git show "0cbf849:${test_path}" | rg -n -C 30 \
'^def (_make_redis_conn|_patch_redis|_make_pool)\b|^class TestRedisCacheLayerInvalidateByTags\b'
printf '%s\n' '--- Changed tests from commit ---'
git show "0cbf849:${test_path}" | rg -n -C 38 \
'async def test_invalidate_(holds_one_permit_across_both_commands|starts_no_command_after_context_exit_on_cancel)\b'
printf '%s\n' '--- Redis constructor patch call sites from commit ---'
git show "0cbf849:${test_path}" | rg -n -C 6 \
'_patch_redis\(|redis\.Redis'Length of output: 28446
The revised permit-scope rationale is correct. It now describes the actual policy: one permit bounds concurrent tag invalidations and keeps each The cancellation test instruments the same No blocking findings. 🐇 ✅ If you found this review helpful, would you consider giving us a shout-out on X? Thank you for using CodeRabbit! ✅ Action performedReview finished.
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CodeRabbit's adversarial review of #1262 found the permit-scope comment factually wrong: it claimed holding one permit across the smembers/delete pair keeps concurrently-held pool connections at the permit count "instead of twice it". redis.asyncio checks a connection out only for each command and returns it to the pool between the two awaits, so acquiring the permit per command would cap in-flight commands at the same limit. The real reason to hold across the pair is scheduling determinism and avoiding permit churn, not preventing a doubling of held connections. - Rewrite the inline comment in invalidate_by_tags() to state the true policy. - Fix the matching docstring of test_invalidate_holds_one_permit_across_both_commands. - Add test_invalidate_starts_no_command_after_context_exit_on_cancel, the cancellation regression guard CodeRabbit asked for: cancel mid-smembers and assert no Redis command starts after the connection context manager exits. No behaviour change; scheduling and return values are untouched. 163 passed. Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com> Claude-Session: https://claude.ai/code/session_01RJP3fieq6JJdEAZXQsJ3J6
0cbf849 to
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Blocked at the governance gate — canonical-duplicate collision with #1265The PR Governance check on head Root cause. #1265 ( Recommended resolution (a human decision — both PRs are yours):
Once #1265 no longer links #1261, re-run PR Governance here and this gate clears. I've left #1265 untouched — it's an active draft with CodeRabbit mid-review, so its history is yours to rewrite, not mine. State of this PR otherwise: the one substantive CodeRabbit finding (permit-scope rationale) is fixed and CodeRabbit-confirmed ( Generated by Claude Code |
The cancellation guard added in e0ebdb3 passes against the pre-change serial implementation on main, so it cannot detect a regression back to sequential invalidation, and its smembers mock has no try/finally, so it never observes whether a cancelled child actually unwound. Measured: running it against `git show origin/main:intelligent_cache.py` yields 1 passed. Replace it with test_invalidate_cancellation_drains_before_conn_closes, which asserts a strict superset: - all three tags are in flight concurrently, via a bounded wait that fails with a diagnostic instead of hanging when they are not; - every cancelled child runs its finally before __aexit__ closes the connection (recorded by a try/finally in the smembers mock); - no Redis command starts after __aexit__ (the original assertion). Against pristine main this test fails, taking the class prove-fail count from 3 to 4. Also notes in the permit-scope comment that holding one permit across the pair bounds how many tags can sit half-invalidated when a delete fails. Full file 163 passed; wider sweep 474 passed; ruff parity unchanged. Co-authored-by: Copilot App <223556219+Copilot@users.noreply.github.com>
Correction: CodeRabbit was right about permit scopeI verified the finding against the redis-py source rather than arguing from memory, and CodeRabbit is correct. My rationale was false. I have retracted it.
conn = self.connection or await pool.get_connection() # borrowed per command
...
finally:
if not self.connection:
await pool.release(conn) # released per commandNo connection is held across the The code is unchanged and remains correct — only the justification was wrong. The honest reason to hold one permit across the pair is a scheduling policy: it bounds how many tag invalidations are in progress, keeps each causally-ordered pair indivisible, and bounds how many tags can sit half-invalidated when a Retracted in all three places it appeared:
The affected test's assertion was already correct; only its stated justification was wrong, so that fix is prose-only. Your other four pointsRecorded as settled, not re-litigated: cancellation parity, the failure path returning A duplicate commit landed on this branch, and I replaced part of itWhile I was preparing the fix above, another agent pushed Its comment prose won and was kept. It states outright that the scope does not lower peak pool-connection usage, which pre-empts the exact wrong inference I originally made. I added one clause it omitted: the half-invalidated-tag bound. Its cancellation test was replaced, because it is vacuous. I ran It passes against the pre-change serial implementation, so it cannot detect a regression back to sequential invalidation. Its
Against pristine The bounded wait matters on its own. My first draft used a bare Note on the approving review aboveThe Current state
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Two quick reconciliations, then I'll stand down since you're driving this. 1. Agreed on the permit-scope retraction and the test swap. Your 2. One gap in the "reds are just the rate-limited Security Scan / trivy" read. Separate from those, on head For the record, everything else on #1262 is green (Vercel, Generated by Claude Code |
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@coderabbitai review The permit-scope finding is remediated in all three locations (source comment, test docstring, PR body) with an explicit retraction and the |
🧩 Analysis chain🏁 Script executed: #!/bin/bash
set -euo pipefail
repo="groupthinking/EventRelay"
pr="1262"
echo '--- PR metadata and checks ---'
gh pr view "$pr" --repo "$repo" \
--json headRefOid,baseRefOid,mergeable,reviewDecision,statusCheckRollup \
--jq '{headRefOid, baseRefOid, mergeable, reviewDecision, checks: [.statusCheckRollup[] | {name, conclusion, status}]}'
echo '--- Changed files ---'
gh pr view "$pr" --repo "$repo" --json files \
--jq '.files[] | {path, additions, deletions}'
echo '--- Focused diff ---'
gh pr diff "$pr" --repo "$repo" -- \
src/youtube_extension/backend/services/intelligent_cache.py \
tests/unit/test_intelligent_cache.py
echo '--- Source outline ---'
ast-grep outline src/youtube_extension/backend/services/intelligent_cache.py \
--items all --type class,function \
--match 'RedisCacheLayer|invalidate_by_tags|_get_tag_write_semaphore|set' \
--view expanded || true
echo '--- Current implementation ---'
rg -n -C 25 \
'async def (invalidate_by_tags|set)\b|def _get_tag_write_semaphore\b|class RedisCacheLayer\b' \
src/youtube_extension/backend/services/intelligent_cache.py
echo '--- Focused test implementations ---'
rg -n -C 45 \
'async def test_invalidate_(cancellation_drains_before_conn_closes|holds_one_permit_across_both_commands|.*concurr|.*failure)' \
tests/unit/test_intelligent_cache.py
echo '--- Base version of cancellation-test region (must be absent or materially different) ---'
base=$(gh pr view "$pr" --repo "$repo" --json baseRefOid --jq '.baseRefOid')
git show "${base}:tests/unit/test_intelligent_cache.py" 2>/dev/null | \
rg -n -C 20 \
'async def test_invalidate_(cancellation_drains_before_conn_closes|holds_one_permit_across_both_commands|.*concurr|.*failure)' || trueLength of output: 5879 🏁 Script executed: #!/bin/bash
set -euo pipefail
base="189c2d2e74f8ce0ffa3a4a5e58d37101a33382d5"
echo '--- Focused diff from PR base ---'
git diff --unified=80 "$base" -- \
src/youtube_extension/backend/services/intelligent_cache.py \
tests/unit/test_intelligent_cache.py
echo '--- Current RedisCacheLayer implementation ---'
rg -n -C 35 \
'class RedisCacheLayer\b|def _get_tag_write_semaphore\b|async def (set|invalidate_by_tags)\b' \
src/youtube_extension/backend/services/intelligent_cache.py
echo '--- Current focused tests ---'
rg -n -C 60 \
'async def test_invalidate_(cancellation_drains_before_conn_closes|holds_one_permit_across_both_commands|.*concurr|.*failure)' \
tests/unit/test_intelligent_cache.py
echo '--- Test helpers used by the cancellation test ---'
rg -n -C 30 \
'^def (_make_redis_conn|_make_pool|_patch_redis)\b|^class TestRedisCacheLayerInvalidateByTags\b' \
tests/unit/test_intelligent_cache.py
echo '--- Base test equivalents ---'
git show "${base}:tests/unit/test_intelligent_cache.py" | \
rg -n -C 30 \
'async def test_invalidate_(cancellation_drains_before_conn_closes|holds_one_permit_across_both_commands|.*concurr|.*failure)' || true
echo '--- Base invalidate_by_tags implementation ---'
git show "${base}:src/youtube_extension/backend/services/intelligent_cache.py" | \
rg -n -C 35 \
'class RedisCacheLayer\b|async def invalidate_by_tags\b|def _get_tag_write_semaphore\b' || trueLength of output: 52472
The permit-scope correction is accurate. The source comment now states that one permit bounds concurrent tag invalidations and keeps each
The current check data includes successful 🐇 ✅ ✅ Action performedReview finished.
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Remediation run — terminal state:
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Canonical issue
Closes #1261.
Outcome
smembers/deletepairs inRedisCacheLayer.invalidate_by_tags()concurrently instead of one tag at a time, so the caller's wall-clock latency stops growing linearly with tag count.set()in #1152) so the combined fan-out cannot exhaust the sharedredis.asyncioconnection pool.smembers->deletepair indivisible.exceptpath that returns0.await conn.smembers(...)already yields; this is a latency defect, not a loop-starvation one. See "Risk" for the honest framing.IntelligentCacheSystem.invalidate_by_tags(), which fans out across layers sequentially. That is a separate defect and is not addressed here.Scope
Two files.
src/youtube_extension/backend/services/intelligent_cache.pyinvalidate_by_tags()— the serialfor tag in tags:body becomes an inner_invalidate_tag()coroutine acquiring the semaphore, gathered withreturn_exceptions=True, with the first exception re-raised so the existingexcept Exceptionhandler still returns0._get_tag_write_semaphore()docstring — two statements became false and are corrected. It previously said the semaphore was "shared by everyset()call" and listedinvalidate_by_tags()among the methods "none of which this limiter touches". Both now name the second caller.tests/unit/test_intelligent_cache.py— five tests appended to the existingTestRedisCacheLayerInvalidateByTagsclass. No existing test was modified.No empty-input guard is needed:
await asyncio.gather()with zero coroutines returns[], so the empty-tag path logs and returns0exactly as before. This is covered by the untouchedtest_invalidate_empty_tags_returns_zero.Overlap with open PR #1179
PR #1179 (loop-ownership contract, tracking issue #1162) edits the same
_get_tag_write_semaphore()docstring. Whichever of the two merges second will hit atextual conflict, and the resolution is mechanical. Disclosing it here so the second
merger does not have to reverse-engineer intent:
set()call becomes tag fan-outset()call", which this PR makes false by adding a second acquirer.This PR could have avoided the third row by leaving the Scope note alone, but that
paragraph lists
invalidate_by_tags()among the methods "none of which this limitertouches" -- a statement this PR makes false. Shipping a knowingly-false docstring to dodge
a conflict is the worse trade, so the edit stays.
There is no functional overlap: #1179 changes connection and loop-ownership bookkeeping,
this PR changes only how the per-tag awaits are scheduled.
Risk
This is a latency change, not a throughput change. Unlike the blocking-call fixes in #1228 / #1240 / #1245, the awaits here already yield to the event loop, so other coroutines were never starved. The cost being removed is borne by the caller awaiting
invalidate_by_tags(). A secondary effect is that the window during which entries meant to be invalidated remain readable byget()shrinks.Behaviour change on the failure path, disclosed deliberately. The serial loop stopped at the first failing tag, leaving later tags untouched. The concurrent version has already issued every tag before the error surfaces, so more tags may be invalidated before the method returns. The return value is identical (
0) in both cases, and the existingtest_invalidate_exception_returns_zeropasses unmodified. For an invalidation path this errs safe: over-invalidating costs a cache miss, under-invalidating leaves stale entries readable.Cancellation parity. If the gather future is itself cancelled,
gathercancels its children and raises without draining them, so a child could still be unwinding when the enclosingasync with redis.Redis(...)closesconn. A cancelled child only unwinds — it releases the semaphore infinallyand lets redis-py return its connection to the pool. It never issues a new command on the closed connection. This is byte-for-byte the same ownership model as theset()fan-out merged in #1152, so this change introduces no new cancellation window.Permit scope (corrected after review). One permit covers both commands for a tag rather than one each. The original justification in this PR was wrong and has been retracted in the code, the test docstring, and here.
The claim was that holding one permit across the pair keeps concurrently-held pool connections equal to the permit count "instead of twice it". That is false.
redis.asyncio.Redisis built withsingle_connection_client=False, soexecute_commandborrows a connection at the start of every command and releases it in afinally:No connection is held across the
awaitboundary betweensmembersanddelete, so a per-command permit would cap in-flight commands at the same number. Peak pool usage is identical either way.The real reason to hold across the pair is a scheduling policy: it bounds how many tag invalidations are in progress at once, keeps each causally-ordered pair indivisible, and bounds how many tags can sit half-invalidated if a
deletefails.test_invalidate_holds_one_permit_across_both_commandspins that policy so a later refactor cannot silently split the pair.Verification
Non-vacuity
Measured against a mock pool with
max_connections=20and a 50-tag invalidation, varying only the limiter:main)The resolved budget is 8 because
_resolve_tag_write_limit()reservesTAG_WRITE_POOL_RESERVE = 4connections for non-tag traffic.Prove-fail
The six new tests were run against the pre-change source. Four fail, which is the guard against a vacuous suite:
Two of the six pass both before and after, and are documented as such rather than presented as proof of the change:
test_invalidate_stays_within_concurrency_bound— a serial loop trivially satisfiespeak <= limit. It guards against a future change removing the limiter.test_invalidate_holds_one_permit_across_both_commands— a serial loop is naturally ordered. It pins the permit-scope decision above so a later refactor cannot silently split the pair.Tests added
test_invalidate_issues_tags_concurrentlytest_invalidate_stays_within_concurrency_bound_tag_write_limittest_invalidate_holds_one_permit_across_both_commandssmembers/deletepairs do not interleavetest_invalidate_cancellation_drains_before_conn_closesfinallycompletes before__aexit__, and no command starts after closetest_invalidate_failure_drains_in_flight_work0withstarted == finishedtest_invalidate_shares_tag_write_budget_with_setset()+invalidate_by_tags()share one budgetCommands
All six pre-existing
invalidate_*tests pass unmodified. Ruff was run on both files against theirorigin/maincounterparts and the diagnostic sets are identical.Production evidence
Not applicable. This change touches a backend Redis cache path that is not exercised by the Vercel preview deployment, and it is behaviour-preserving — the same keys and members are read and deleted, only the scheduling of the awaits changes. Correctness is covered by the five focused unit tests above rather than by a runtime deployment.
Agent handoff