perf(ring): cache ShuffleShardWithLookback subrings#7628
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| // For subrings returned by ShuffleShardWithLookback, the time at which the subring's | ||
| // membership would next change because an instance falls out of the lookback window. | ||
| // Zero means the subring has no time-based expiry (membership only changes with topology). | ||
| shuffleShardExpiry time.Time |
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Should we create a wrapper for the cached ring? It seems odd that we are mixing ring and cached data.
Something as
type Ring struct {
// ... domain fields ...
shuffledSubringCache map[subringCacheKey]*cachedSubring
}
type cachedSubring struct {
ring *Ring // the subring itself (no cache metadata on it)
shuffleShardExpiry time.Time
}
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Previously we used Ring for both cached and normal so I didn't think of that.
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Done - added the wrapper
Signed-off-by: Ahmed Hassan <afayekhassan@gmail.com>
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What this PR does
Add caching for
ShuffleShardWithLookbacksubrings. Previously, the shuffle shard lookback variantrecomputed on every call because its membership is time-dependent and could not be
represented by the existing topology-keyed cache.
New
ShuffleShardWithLookbackcacheA lookback subring's membership can only change for one of two reasons, and each is
covered by an invalidation path:
to/from
READONLY) — invalidates the entireshuffledSubringCachevialastTopologyChange.EqualButReadOnlyis treated as a topology change for thispurpose, so READONLY-driven inclusion changes are covered here.
shuffleShardrecordsshuffleShardExpiry = min(RegisteredTimestamp + lookbackPeriod)across all lookback-included instances on the subring.
getCachedShuffledSubringtreats the entry as a miss once
now >= shuffleShardExpiry, forcing a recompute.Implementation notes
subringCacheKeygainslookbackPeriodso lookback subrings don't collide withplain ones.
shuffleShardExpiry == 0andbehave like plain subrings (only topology invalidates).
Tests
Added
TestShuffleShardWithLookbackCachinginpkg/ring/ring_test.go, covering:timestamps refreshed on hit.
nowpastRegisteredTimestamp + lookbackPeriodforces a recompute andthe new subring shrinks (instances fall out of the window).
cached.
(user, size)are cached under separatekeys.
CleanupShuffleShardCacheevicts the entry.
Checklist
CHANGELOG.mdupdated - the order of entries should be[CHANGE],[FEATURE],[ENHANCEMENT],[BUGFIX]docs/configuration/v1-guarantees.mdupdated if this PR introduces experimental flags