perf(ingester): lazy regex evaluation on head postings cache miss#7553
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Nice work! Just some nits
When the expanded postings cache misses on the head block, regex matchers on high-cardinality labels (e.g. pod with 400K+ values) dominate query cost. This PR defers expensive regex matchers to a lazy per-series evaluation when a selective equality matcher already narrows the result set significantly. On cache miss, splitMatchersForHeadWithConfig splits matchers into: - Selective matchers (equality, low-card regex) for postings lookup - Lazy matchers (high-card regex) applied per-series via LabelValueFor A cost-ratio gate decides when deferral is worthwhile: - Simple regex (single contains, prefix): cardinality > selectivePostings * 6 - Complex regex (multi-substring, capture groups): cardinality > selectivePostings * 2 Label cardinality lookups are cached in an expirable LRU (60s TTL) to avoid repeated LabelValues calls under load. Benchmark (realistic pod names, 413K cardinality, 9K selective postings): - Eager: 62ms, 29.8MB per query - Lazy: 14ms, 12.6MB per query (4.5x faster, 58% less memory) New flags (disabled by default with max-cardinality=0): - blocks-storage.expanded_postings_cache.head.lazy-matcher-max-cardinality - blocks-storage.expanded_postings_cache.head.lazy-matcher-simple-cost-ratio - blocks-storage.expanded_postings_cache.head.lazy-matcher-complex-cost-ratio
Co-authored-by: SungJin1212 <tjdwls1201@gmail.com> Signed-off-by: Alan Protasio <alanprot@gmail.com>
…pagation test - Mark all lazy-matcher flags as [EXPERIMENTAL] per v1 guarantee - Use errors.Is(err, storage.ErrNotFound) instead of direct comparison - Propagate non-ErrNotFound errors from LabelValueFor - Add TestFetchWithLazyMatchers_PropagatesLabelValueForError - Skip SetMatches matchers from lazy candidates (already fast-pathed) - Remove dead SetMatches check from regexCostClass - Regenerate docs and schema
Signed-off-by: Alan Protasio <approtas@amazon.com>
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Lazy regex evaluation on head postings cache miss
When the expanded postings cache misses on the head block, regex matchers on high-cardinality labels (e.g.,
podwith 400K+ values) dominate query cost — the regex runs against every label value to build the posting list.This PR defers expensive regex matchers to a lazy per-series evaluation when a selective equality matcher (like
__name__=) already narrows the result set significantly.How it works
On cache miss,
splitMatchersForHeadWithConfigsplits matchers into:LabelValueForafter the selective postings are resolvedA cost-ratio gate decides when deferral is worthwhile:
cardinality > selectivePostings × 6cardinality > selectivePostings × 2Label cardinality lookups are cached in an expirable LRU (60s TTL) to avoid repeated
LabelValuescalls under load.Benchmark results (realistic pod names, 413K cardinality, 9K selective postings)
Configuration
Three new flags (all disabled by default —
max-cardinality=0):Testing
TestLazyMatchersFuzz): 300 fuzzed queries + injected regex patterns compared between eager and lazy instances — 450+ lazy triggers, zero mismatchesChecklist
CHANGELOG.mdupdated - the order of entries should be[CHANGE],[FEATURE],[ENHANCEMENT],[BUGFIX]docs/configuration/v1-guarantees.mdupdated if this PR introduces experimental flags