fix: set correct number of keys in background cache metrics (#2764)

Signed-off-by: Trevor Wood <[email protected]>

Co-authored-by: Marco Pracucci <[email protected]>

Author: taharah

CHANGELOG.md

@@ -139,6 +139,7 @@
 * [BUGFIX] Cassandra: fixed an edge case leading to an invalid CQL query when querying the index on a Cassandra store. #2639
 * [BUGFIX] Ingester: increment series per metric when recovering from WAL or transfer. #2674
 * [BUGFIX] Fixed `wrong number of arguments for 'mget' command` Redis error when a query has no chunks to lookup from storage. #2700
+* [BUGFIX] Fixed the number of reported keys in the background cache queue. #2764
 * [BUGFIX] Ingester: Automatically remove old tmp checkpoints, fixing a potential disk space leak after an ingester crashes.
 * [BUGFIX] Fix race in processing of headers in sharded queries. #2762
 

pkg/chunk/cache/background.go

@@ -96,12 +96,12 @@ func (c *backgroundCache) Store(ctx context.Context, keys []string, bufs [][]byt
 		}
 		select {
 		case c.bgWrites <- bgWrite:
-			c.queueLength.Add(float64(len(keys)))
+			c.queueLength.Add(float64(num))
 		default:
-			c.droppedWriteBack.Add(float64(len(keys)))
+			c.droppedWriteBack.Add(float64(num))
 			sp := opentracing.SpanFromContext(ctx)
 			if sp != nil {
-				sp.LogFields(otlog.Int("dropped", len(keys)))
+				sp.LogFields(otlog.Int("dropped", num))
 			}
 			return // queue is full; give up
 		}