Reduce memSeries memory usage by decoupling metadata (#11152)

Metadata was added recently but doesn't seem to be used much, at least as far as I could identify.
Yet it's part of memSeries struct and so even when empty takes 48 bytes,
which is a lot given that without it memSeries requires 224 bytes.
This change turns it into a pointer on the struct, that get set only when metadata is actually set of given series.

Signed-off-by: Łukasz Mierzwa <l.mierzwa@gmail.com>

Signed-off-by: Łukasz Mierzwa <l.mierzwa@gmail.com>

tsdb/db_test.go

@@ -1821,10 +1821,10 @@ func TestQuerierWithBoundaryChunks(t *testing.T) {
 }
 
 // TestInitializeHeadTimestamp ensures that the h.minTime is set properly.
-// 	- no blocks no WAL: set to the time of the first  appended sample
-// 	- no blocks with WAL: set to the smallest sample from the WAL
-//	- with blocks no WAL: set to the last block maxT
-// 	- with blocks with WAL: same as above
+//   - no blocks no WAL: set to the time of the first  appended sample
+//   - no blocks with WAL: set to the smallest sample from the WAL
+//   - with blocks no WAL: set to the last block maxT
+//   - with blocks with WAL: same as above
 func TestInitializeHeadTimestamp(t *testing.T) {
 	t.Run("clean", func(t *testing.T) {
 		dir := t.TempDir()
@@ -2166,10 +2166,12 @@ func TestCorrectNumTombstones(t *testing.T) {
 }
 
 // TestBlockRanges checks the following use cases:
-//  - No samples can be added with timestamps lower than the last block maxt.
-//  - The compactor doesn't create overlapping blocks
+//   - No samples can be added with timestamps lower than the last block maxt.
+//   - The compactor doesn't create overlapping blocks
+//
 // even when the last blocks is not within the default boundaries.
-//	- Lower boundary is based on the smallest sample in the head and
+//   - Lower boundary is based on the smallest sample in the head and
+//
 // upper boundary is rounded to the configured block range.
 //
 // This ensures that a snapshot that includes the head and creates a block with a custom time range
@@ -3697,10 +3699,10 @@ func TestMetadataAssertInMemoryData(t *testing.T) {
 	series2 := db.head.series.getByHash(s2.Hash(), s2)
 	series3 := db.head.series.getByHash(s3.Hash(), s3)
 	series4 := db.head.series.getByHash(s4.Hash(), s4)
-	require.Equal(t, series1.meta, m1)
-	require.Equal(t, series2.meta, m2)
-	require.Equal(t, series3.meta, m3)
-	require.Equal(t, series4.meta, metadata.Metadata{})
+	require.Equal(t, *series1.meta, m1)
+	require.Equal(t, *series2.meta, m2)
+	require.Equal(t, *series3.meta, m3)
+	require.Nil(t, series4.meta)
 
 	// Add a replicated metadata entry to the first series,
 	// a changed metadata entry to the second series,
@@ -3718,10 +3720,10 @@ func TestMetadataAssertInMemoryData(t *testing.T) {
 	series2 = db.head.series.getByHash(s2.Hash(), s2)
 	series3 = db.head.series.getByHash(s3.Hash(), s3)
 	series4 = db.head.series.getByHash(s4.Hash(), s4)
-	require.Equal(t, series1.meta, m1)
-	require.Equal(t, series2.meta, m5)
-	require.Equal(t, series3.meta, m3)
-	require.Equal(t, series4.meta, m4)
+	require.Equal(t, *series1.meta, m1)
+	require.Equal(t, *series2.meta, m5)
+	require.Equal(t, *series3.meta, m3)
+	require.Equal(t, *series4.meta, m4)
 
 	require.NoError(t, db.Close())
 
@@ -3736,8 +3738,8 @@ func TestMetadataAssertInMemoryData(t *testing.T) {
 	_, err = reopenDB.head.wal.Size()
 	require.NoError(t, err)
 
-	require.Equal(t, reopenDB.head.series.getByHash(s1.Hash(), s1).meta, m1)
-	require.Equal(t, reopenDB.head.series.getByHash(s2.Hash(), s2).meta, m5)
-	require.Equal(t, reopenDB.head.series.getByHash(s3.Hash(), s3).meta, m3)
-	require.Equal(t, reopenDB.head.series.getByHash(s4.Hash(), s4).meta, m4)
+	require.Equal(t, *reopenDB.head.series.getByHash(s1.Hash(), s1).meta, m1)
+	require.Equal(t, *reopenDB.head.series.getByHash(s2.Hash(), s2).meta, m5)
+	require.Equal(t, *reopenDB.head.series.getByHash(s3.Hash(), s3).meta, m3)
+	require.Equal(t, *reopenDB.head.series.getByHash(s4.Hash(), s4).meta, m4)
 }

tsdb/head.go

@@ -1516,7 +1516,7 @@ type memSeries struct {
 
 	ref  chunks.HeadSeriesRef
 	lset labels.Labels
-	meta metadata.Metadata
+	meta *metadata.Metadata
 
 	// Immutable chunks on disk that have not yet gone into a block, in order of ascending time stamps.
 	// When compaction runs, chunks get moved into a block and all pointers are shifted like so:
@@ -1540,8 +1540,6 @@ type memSeries struct {
 	// Even the most compact encoding of a sample takes 2 bits, so the last byte is not contended.
 	sampleBuf [4]sample
 
-	pendingCommit bool // Whether there are samples waiting to be committed to this series.
-
 	// Current appender for the head chunk. Set when a new head chunk is cut.
 	// It is nil only if headChunk is nil. E.g. if there was an appender that created a new series, but rolled back the commit
 	// (the first sample would create a headChunk, hence appender, but rollback skipped it while the Append() call would create a series).
@@ -1551,6 +1549,8 @@ type memSeries struct {
 
 	// txs is nil if isolation is disabled.
 	txs *txRing
+
+	pendingCommit bool // Whether there are samples waiting to be committed to this series.
 }
 
 func newMemSeries(lset labels.Labels, id chunks.HeadSeriesRef, chunkRange int64, memChunkPool *sync.Pool, isolationDisabled bool) *memSeries {

tsdb/head_append.go

@@ -399,7 +399,7 @@ func (a *headAppender) UpdateMetadata(ref storage.SeriesRef, lset labels.Labels,
 	}
 
 	s.RLock()
-	hasNewMetadata := s.meta != meta
+	hasNewMetadata := s.meta == nil || *s.meta != meta
 	s.RUnlock()
 
 	if hasNewMetadata {
@@ -540,7 +540,7 @@ func (a *headAppender) Commit() (err error) {
 	for i, m := range a.metadata {
 		series = a.metadataSeries[i]
 		series.Lock()
-		series.meta = metadata.Metadata{Type: record.ToTextparseMetricType(m.Type), Unit: m.Unit, Help: m.Help}
+		series.meta = &metadata.Metadata{Type: record.ToTextparseMetricType(m.Type), Unit: m.Unit, Help: m.Help}
 		series.Unlock()
 	}
 

tsdb/head_wal.go

@@ -333,7 +333,7 @@ Outer:
 					unknownMetadataRefs.Inc()
 					continue
 				}
-				s.meta = metadata.Metadata{
+				s.meta = &metadata.Metadata{
 					Type: record.ToTextparseMetricType(m.Type),
 					Unit: m.Unit,
 					Help: m.Help,