From b749b66a96359f3d984a92ca3dbfa1a0784e5ed5 Mon Sep 17 00:00:00 2001
From: Bo Du <bo@chronosphere.io>
Date: Fri, 20 Nov 2020 00:14:15 -0500
Subject: [PATCH] Extend the on flush new series event to account for differing
 types of series metadata and memory lifetimes.

---
 src/dbnode/persist/fs/merger.go | 13 +++++++---
 src/dbnode/persist/types.go     | 43 ++++++++++++++++++++++++++++++---
 2 files changed, 48 insertions(+), 8 deletions(-)

diff --git a/src/dbnode/persist/fs/merger.go b/src/dbnode/persist/fs/merger.go
index 555bbcc6d8..b3fc9f2e6d 100644
--- a/src/dbnode/persist/fs/merger.go
+++ b/src/dbnode/persist/fs/merger.go
@@ -249,10 +249,15 @@ func (m *merger) Merge(
 
 			if err == nil {
 				err = onFlush.OnFlushNewSeries(persist.OnFlushNewSeriesEvent{
-					Shard:          shard,
-					BlockStart:     startTime,
-					FirstWrite:     mergeWithData.FirstWrite,
-					SeriesMetadata: seriesMetadata,
+					Shard:      shard,
+					BlockStart: startTime,
+					FirstWrite: mergeWithData.FirstWrite,
+					SeriesMetadata: persist.SeriesMetadata{
+						Type:     persist.SeriesDocumentType,
+						Document: seriesMetadata,
+						// The lifetime of the shard series metadata is longly lived.
+						LifeTime: persist.SeriesMetadataLifeTimeLongLived,
+					},
 				})
 			}
 
diff --git a/src/dbnode/persist/types.go b/src/dbnode/persist/types.go
index f93f28bb56..dc18d7d319 100644
--- a/src/dbnode/persist/types.go
+++ b/src/dbnode/persist/types.go
@@ -35,9 +35,7 @@ import (
 	"github.com/pborman/uuid"
 )
 
-var (
-	errReuseableTagIteratorRequired = errors.New("reuseable tags iterator is required")
-)
+var errReuseableTagIteratorRequired = errors.New("reuseable tags iterator is required")
 
 // Metadata is metadata for a time series, it can
 // have several underlying sources.
@@ -322,12 +320,49 @@ const (
 	FileSetIndexContentType
 )
 
+// SeriesMetadataLifeTime describes the memory life time type.
+type SeriesMetadataLifeTime int
+
+const (
+	// SeriesMetadataLifeTimeLongLived means the underlying memory's life time is long lived and exceeds
+	// the execution duration of the series metadata receiver.
+	SeriesMetadataLifeTimeLongLived SeriesMetadataLifeTime = iota
+	// SeriesMetadataLifeTimeShortLived means that the underlying memory is only valid for the duration
+	// of the OnFlushNewSeries call. Must clone the underlying bytes in order to extend the life time.
+	SeriesMetadataLifeTimeShortLived
+)
+
+// SeriesMetadataType describes the type of series metadata.
+type SeriesMetadataType int
+
+const (
+	// SeriesDocumentType means the metadata is in doc.Document form.
+	SeriesDocumentType SeriesMetadataType = iota
+	// SeriesIDAndEncodedTagsType means the metadata is in IDAndEncodedTags form.
+	SeriesIDAndEncodedTagsType
+)
+
+// IDAndEncodedTags contains a series ID and encoded tags.
+type IDAndEncodedTags struct {
+	ID          []byte
+	EncodedTags []byte
+}
+
+// SeriesMetadata captures different representations of series metadata and
+// the ownership status of the underlying memory.
+type SeriesMetadata struct {
+	Type             SeriesMetadataType
+	LifeTime         SeriesMetadataLifeTime
+	Document         doc.Document
+	IDAndEncodedTags IDAndEncodedTags
+}
+
 // OnFlushNewSeriesEvent is the fields related to a flush of a new series.
 type OnFlushNewSeriesEvent struct {
 	Shard          uint32
 	BlockStart     time.Time
 	FirstWrite     time.Time
-	SeriesMetadata doc.Document
+	SeriesMetadata SeriesMetadata
 }
 
 // OnFlushSeries performs work on a per series level.