Cherry pick PR 2998 into release 1.3 branch (#3001)

* Add chunk flush outcome "Dropped", for short series (#2998)

If the series is below a configured length it gets dropped instead of
flushed.  Add a separate `outcome` for this case, otherwise it is
reported as "NoChunksToFlush".

Signed-off-by: Bryan Boreham <[email protected]>

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

* Updated CHANGELOG

Signed-off-by: Marco Pracucci <[email protected]>

Co-authored-by: Bryan Boreham <[email protected]>

Author: pracucci

CHANGELOG.md

@@ -11,7 +11,7 @@
   * `cortex_bucket_stores_gate_queries_concurrent_max`
   * `cortex_bucket_stores_gate_queries_in_flight`
   * `cortex_bucket_stores_gate_duration_seconds`
-* [CHANGE] Metric `cortex_ingester_flush_reasons` has been renamed to `cortex_ingester_flushing_enqueued_series_total`, and new metric `cortex_ingester_flushing_dequeued_series_total` with `outcome` label (superset of reason) has been added. #2802, #2818
+* [CHANGE] Metric `cortex_ingester_flush_reasons` has been renamed to `cortex_ingester_flushing_enqueued_series_total`, and new metric `cortex_ingester_flushing_dequeued_series_total` with `outcome` label (superset of reason) has been added. #2802 #2818 #2998
 * [CHANGE] Experimental Delete Series: Metric `cortex_purger_oldest_pending_delete_request_age_seconds` would track age of delete requests since they are over their cancellation period instead of their creation time. #2806
 * [CHANGE] Experimental blocks storage: the store-gateway service is required in a Cortex cluster running with the experimental blocks storage. Removed the `-experimental.tsdb.store-gateway-enabled` CLI flag and `store_gateway_enabled` YAML config option. The store-gateway is now always enabled when the storage engine is `blocks`. #2822
 * [CHANGE] Experimental blocks storage: removed support for `-experimental.blocks-storage.bucket-store.max-sample-count` flag because the implementation was flawed. To limit the number of samples/chunks processed by a single query you can set `-store.query-chunk-limit`, which is now supported by the blocks storage too. #2852

pkg/ingester/flush.go

@@ -111,6 +111,7 @@ const (
 	noSeries
 	noChunks
 	flushError
+	reasonDropped
 	maxFlushReason // Used for testing String() method. Should be last.
 )
 
@@ -138,6 +139,8 @@ func (f flushReason) String() string {
 		return "NoChunksToFlush"
 	case flushError:
 		return "FlushError"
+	case reasonDropped:
+		return "Dropped"
 	default:
 		panic("unrecognised flushReason")
 	}
@@ -307,12 +310,17 @@ func (i *Ingester) flushUserSeries(flushQueueIndex int, userID string, fp model.
 					"queue", flushQueueIndex,
 				)
 				chunks = nil
+				reason = reasonDropped
 			}
 		}
 	}
 
 	userState.fpLocker.Unlock(fp)
 
+	if reason == reasonDropped {
+		return reason, nil
+	}
+
 	// No need to flush these chunks again.
 	for len(chunks) > 0 && chunks[0].flushed {
 		chunks = chunks[1:]