recomputeStats() wrote statSum/statSamples/statMin/statMax/statsValid from
inside the stats() fast path, which runs under only a shared RLock via
MemoryStore.Stats -> Level.findBuffers. Two concurrent queries on the same
invalid buffer could both enter the fast path and race on those fields.
Require statsValid in the fast-path guard instead of recomputing inline;
invalid buffers now fall through to the existing point-by-point scan, which
only reads b.data. recomputeStats() is unchanged and still used by
checkpoint loadFile at single-threaded load time.
Updated stats_test.go: overwritten buffers now stay statsValid=false after a
query (documenting non-mutating reads); TestStatsMultiBufferChain and
TestStatsFastPathThenPartialTail now recompute stats after building bare
buffers so the fast-path cache fold is still covered; added
TestStatsConcurrentQueriesNoRace (race-clean under -race for both valid and
post-overwrite buffers) and TestStatsGappedChain (real inter-buffer gap
correctly excluded from Samples/Min/Max/Avg).
Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>
Add len(b.data) > 0 guard to prevent infinite loop when an empty linked
buffer is reachable. With the guard false, the normal path handles empty
buffers safely via the existing t < b.start || idx >= len(b.data) check.
Add regression test TestStatsFastPathThenPartialTail to pin the boundary:
three-buffer chain where earlier buffers are fully covered (fast path) and
the last buffer is partially covered (normal path).
Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>
Aditya Ujeniya