store: reduce memory footprint for chunks queries

CHANGELOG.md

@@ -23,11 +23,13 @@ We use _breaking :warning:_ to mark changes that are not backward compatible (re
 - [#3204](https://github.com/thanos-io/thanos/pull/3204) Mixin: Use sidecar's metric timestamp for healthcheck.
 - [#3922](https://github.com/thanos-io/thanos/pull/3922) Fix panic in http logging middleware.
 - [#3960](https://github.com/thanos-io/thanos/pull/3960) fix deduplication of equal alerts with different labels
+- [#3937](https://github.com/thanos-io/thanos/pull/3937) Store: Fix race condition in chunk pool.
 
 ### Changed
 
 - [#3948](https://github.com/thanos-io/thanos/pull/3948) Receiver: Adjust `http_request_duration_seconds` buckets for low latency requests.
 - [#3856](https://github.com/thanos-io/thanos/pull/3856) Mixin: _breaking :warning:_ Introduce flexible multi-cluster/namespace mode for alerts and dashboards. Removes jobPrefix config option. Removes `namespace` by default.
+- [#3937](https://github.com/thanos-io/thanos/pull/3937) Store: Reduce memory usage for range queries.
 
 ### Removed
 

pkg/pool/pool.go

@@ -112,13 +112,12 @@ func (p *BucketedBytes) Put(b *[]byte) {
 			continue
 		}
 		*b = (*b)[:0]
+		p.mtx.Lock()
+		defer p.mtx.Unlock()
 		p.buckets[i].Put(b)
 		break
 	}
 
-	p.mtx.Lock()
-	defer p.mtx.Unlock()
-
 	// We could assume here that our users will not make the slices larger
 	// but lets be on the safe side to avoid an underflow of p.usedTotal.
 	sz := uint64(cap(*b))