changelog/comments

Signed-off-by: Alan Protasio <[email protected]>

Author: alanprot

CHANGELOG.md

@@ -2,6 +2,8 @@
 
 ## master / unreleased
 
+* [ENHANCEMENT] Querier: Batch Iterator optimization to prevent transversing it multiple times query ranges steps does not overlap. #5237
+
 ## 1.15.0 in progress
 
 * [CHANGE] Storage: Make Max exemplars config per tenant instead of global configuration. #5016

pkg/querier/batch/batch.go

@@ -43,7 +43,7 @@ type iterator interface {
 	// Seek or Next have returned true.
 	AtTime() int64
 
-	// MaxCurrentChunkTime returns the max time on the current chunk
+	// MaxCurrentChunkTime returns the max time on the current chunk.
 	MaxCurrentChunkTime() int64
 
 	// Batch returns the current batch.  Must only be called after Seek or Next
@@ -103,7 +103,10 @@ func (a *iteratorAdapter) Seek(t int64) bool {
 			return true
 		} else if t <= a.underlying.MaxCurrentChunkTime() {
 			// In this case, some timestamp inside the current underlying chunk can fulfill the seek.
-			// In this case we will call next until we find the sample as it will be faster than calling seek directly.
+			// In this case we will call next until we find the sample as it will be faster than calling
+			// `a.underlying.Seek` directly as this would cause the iterator to start from the beginning of the chunk.
+			// See: https://github.com/cortexproject/cortex/blob/f69452975877c67ac307709e5f60b8d20477764c/pkg/querier/batch/chunk.go#L26-L45
+			//      https://github.com/cortexproject/cortex/blob/f69452975877c67ac307709e5f60b8d20477764c/pkg/chunk/encoding/prometheus_chunk.go#L90-L95
 			for a.Next() {
 				if t <= a.curr.Timestamps[a.curr.Index] {
 					return true