feat: Allow customizing TSDB postings decoder (#13567)

* allow customizing TSDB postings decoder

---------

Signed-off-by: Ben Ye <benye@amazon.com>

cmd/promtool/tsdb.go

@@ -405,7 +405,7 @@ func openBlock(path, blockID string) (*tsdb.DBReadOnly, tsdb.BlockReader, error)
 		}
 	}
 
-	b, err := db.Block(blockID)
+	b, err := db.Block(blockID, tsdb.DefaultPostingsDecoderFactory)
 	if err != nil {
 		return nil, nil, err
 	}

tsdb/block.go

@@ -330,7 +330,7 @@ type Block struct {
 
 // OpenBlock opens the block in the directory. It can be passed a chunk pool, which is used
 // to instantiate chunk structs.
-func OpenBlock(logger *slog.Logger, dir string, pool chunkenc.Pool) (pb *Block, err error) {
+func OpenBlock(logger *slog.Logger, dir string, pool chunkenc.Pool, postingsDecoderFactory PostingsDecoderFactory) (pb *Block, err error) {
 	if logger == nil {
 		logger = promslog.NewNopLogger()
 	}
@@ -351,7 +351,11 @@ func OpenBlock(logger *slog.Logger, dir string, pool chunkenc.Pool) (pb *Block,
 	}
 	closers = append(closers, cr)
 
-	ir, err := index.NewFileReader(filepath.Join(dir, indexFilename))
+	decoder := index.DecodePostingsRaw
+	if postingsDecoderFactory != nil {
+		decoder = postingsDecoderFactory(meta)
+	}
+	ir, err := index.NewFileReader(filepath.Join(dir, indexFilename), decoder)
 	if err != nil {
 		return nil, err
 	}

tsdb/block_test.go

@@ -59,14 +59,14 @@ func TestSetCompactionFailed(t *testing.T) {
 	tmpdir := t.TempDir()
 
 	blockDir := createBlock(t, tmpdir, genSeries(1, 1, 0, 1))
-	b, err := OpenBlock(nil, blockDir, nil)
+	b, err := OpenBlock(nil, blockDir, nil, nil)
 	require.NoError(t, err)
 	require.False(t, b.meta.Compaction.Failed)
 	require.NoError(t, b.setCompactionFailed())
 	require.True(t, b.meta.Compaction.Failed)
 	require.NoError(t, b.Close())
 
-	b, err = OpenBlock(nil, blockDir, nil)
+	b, err = OpenBlock(nil, blockDir, nil, nil)
 	require.NoError(t, err)
 	require.True(t, b.meta.Compaction.Failed)
 	require.NoError(t, b.Close())
@@ -74,7 +74,7 @@ func TestSetCompactionFailed(t *testing.T) {
 
 func TestCreateBlock(t *testing.T) {
 	tmpdir := t.TempDir()
-	b, err := OpenBlock(nil, createBlock(t, tmpdir, genSeries(1, 1, 0, 10)), nil)
+	b, err := OpenBlock(nil, createBlock(t, tmpdir, genSeries(1, 1, 0, 10)), nil, nil)
 	require.NoError(t, err)
 	require.NoError(t, b.Close())
 }
@@ -84,7 +84,7 @@ func BenchmarkOpenBlock(b *testing.B) {
 	blockDir := createBlock(b, tmpdir, genSeries(1e6, 20, 0, 10))
 	b.Run("benchmark", func(b *testing.B) {
 		for i := 0; i < b.N; i++ {
-			block, err := OpenBlock(nil, blockDir, nil)
+			block, err := OpenBlock(nil, blockDir, nil, nil)
 			require.NoError(b, err)
 			require.NoError(b, block.Close())
 		}
@@ -190,7 +190,7 @@ func TestCorruptedChunk(t *testing.T) {
 			require.NoError(t, f.Close())
 
 			// Check open err.
-			b, err := OpenBlock(nil, blockDir, nil)
+			b, err := OpenBlock(nil, blockDir, nil, nil)
 			if tc.openErr != nil {
 				require.EqualError(t, err, tc.openErr.Error())
 				return
@@ -245,7 +245,7 @@ func TestLabelValuesWithMatchers(t *testing.T) {
 	require.NotEmpty(t, files, "No chunk created.")
 
 	// Check open err.
-	block, err := OpenBlock(nil, blockDir, nil)
+	block, err := OpenBlock(nil, blockDir, nil, nil)
 	require.NoError(t, err)
 	defer func() { require.NoError(t, block.Close()) }()
 
@@ -325,7 +325,7 @@ func TestBlockQuerierReturnsSortedLabelValues(t *testing.T) {
 	blockDir := createBlock(t, tmpdir, seriesEntries)
 
 	// Check open err.
-	block, err := OpenBlock(nil, blockDir, nil)
+	block, err := OpenBlock(nil, blockDir, nil, nil)
 	require.NoError(t, err)
 	t.Cleanup(func() { require.NoError(t, block.Close()) })
 
@@ -352,7 +352,7 @@ func TestBlockSize(t *testing.T) {
 	// Create a block and compare the reported size vs actual disk size.
 	{
 		blockDirInit = createBlock(t, tmpdir, genSeries(10, 1, 1, 100))
-		blockInit, err = OpenBlock(nil, blockDirInit, nil)
+		blockInit, err = OpenBlock(nil, blockDirInit, nil, nil)
 		require.NoError(t, err)
 		defer func() {
 			require.NoError(t, blockInit.Close())
@@ -377,7 +377,7 @@ func TestBlockSize(t *testing.T) {
 		blockDirsAfterCompact, err := c.Compact(tmpdir, []string{blockInit.Dir()}, nil)
 		require.NoError(t, err)
 		require.Len(t, blockDirsAfterCompact, 1)
-		blockAfterCompact, err := OpenBlock(nil, filepath.Join(tmpdir, blockDirsAfterCompact[0].String()), nil)
+		blockAfterCompact, err := OpenBlock(nil, filepath.Join(tmpdir, blockDirsAfterCompact[0].String()), nil, nil)
 		require.NoError(t, err)
 		defer func() {
 			require.NoError(t, blockAfterCompact.Close())
@@ -408,7 +408,7 @@ func TestReadIndexFormatV1(t *testing.T) {
 	*/
 
 	blockDir := filepath.Join("testdata", "index_format_v1")
-	block, err := OpenBlock(nil, blockDir, nil)
+	block, err := OpenBlock(nil, blockDir, nil, nil)
 	require.NoError(t, err)
 
 	q, err := NewBlockQuerier(block, 0, 1000)
@@ -445,7 +445,7 @@ func BenchmarkLabelValuesWithMatchers(b *testing.B) {
 	require.NotEmpty(b, files, "No chunk created.")
 
 	// Check open err.
-	block, err := OpenBlock(nil, blockDir, nil)
+	block, err := OpenBlock(nil, blockDir, nil, nil)
 	require.NoError(b, err)
 	defer func() { require.NoError(b, block.Close()) }()
 
@@ -497,7 +497,7 @@ func TestLabelNamesWithMatchers(t *testing.T) {
 	require.NotEmpty(t, files, "No chunk created.")
 
 	// Check open err.
-	block, err := OpenBlock(nil, blockDir, nil)
+	block, err := OpenBlock(nil, blockDir, nil, nil)
 	require.NoError(t, err)
 	t.Cleanup(func() { require.NoError(t, block.Close()) })
 
@@ -551,7 +551,7 @@ func TestBlockIndexReader_PostingsForLabelMatching(t *testing.T) {
 		require.NoError(t, err)
 		require.NotEmpty(t, files, "No chunk created.")
 
-		block, err := OpenBlock(nil, blockDir, nil)
+		block, err := OpenBlock(nil, blockDir, nil, nil)
 		require.NoError(t, err)
 		t.Cleanup(func() { require.NoError(t, block.Close()) })
 

tsdb/blockwriter_test.go

@@ -47,7 +47,7 @@ func TestBlockWriter(t *testing.T) {
 
 	// Confirm the block has the correct data.
 	blockpath := filepath.Join(outputDir, id.String())
-	b, err := OpenBlock(nil, blockpath, nil)
+	b, err := OpenBlock(nil, blockpath, nil, nil)
 	require.NoError(t, err)
 	defer func() { require.NoError(t, b.Close()) }()
 	q, err := NewBlockQuerier(b, math.MinInt64, math.MaxInt64)

tsdb/compact.go

@@ -87,6 +87,7 @@ type LeveledCompactor struct {
 	maxBlockChunkSegmentSize    int64
 	mergeFunc                   storage.VerticalChunkSeriesMergeFunc
 	postingsEncoder             index.PostingsEncoder
+	postingsDecoderFactory      PostingsDecoderFactory
 	enableOverlappingCompaction bool
 }
 
@@ -158,6 +159,9 @@ type LeveledCompactorOptions struct {
 	// PE specifies the postings encoder. It is called when compactor is writing out the postings for a label name/value pair during compaction.
 	// If it is nil then the default encoder is used. At the moment that is the "raw" encoder. See index.EncodePostingsRaw for more.
 	PE index.PostingsEncoder
+	// PD specifies the postings decoder factory to return different postings decoder based on BlockMeta. It is called when opening a block or opening the index file.
+	// If it is nil then a default decoder is used, compatible with Prometheus v2.
+	PD PostingsDecoderFactory
 	// MaxBlockChunkSegmentSize is the max block chunk segment size. If it is 0 then the default chunks.DefaultChunkSegmentSize is used.
 	MaxBlockChunkSegmentSize int64
 	// MergeFunc is used for merging series together in vertical compaction. By default storage.NewCompactingChunkSeriesMerger(storage.ChainedSeriesMerge) is used.
@@ -167,6 +171,12 @@ type LeveledCompactorOptions struct {
 	EnableOverlappingCompaction bool
 }
 
+type PostingsDecoderFactory func(meta *BlockMeta) index.PostingsDecoder
+
+func DefaultPostingsDecoderFactory(_ *BlockMeta) index.PostingsDecoder {
+	return index.DecodePostingsRaw
+}
+
 func NewLeveledCompactorWithChunkSize(ctx context.Context, r prometheus.Registerer, l *slog.Logger, ranges []int64, pool chunkenc.Pool, maxBlockChunkSegmentSize int64, mergeFunc storage.VerticalChunkSeriesMergeFunc) (*LeveledCompactor, error) {
 	return NewLeveledCompactorWithOptions(ctx, r, l, ranges, pool, LeveledCompactorOptions{
 		MaxBlockChunkSegmentSize:    maxBlockChunkSegmentSize,
@@ -213,6 +223,7 @@ func NewLeveledCompactorWithOptions(ctx context.Context, r prometheus.Registerer
 		maxBlockChunkSegmentSize:    maxBlockChunkSegmentSize,
 		mergeFunc:                   mergeFunc,
 		postingsEncoder:             pe,
+		postingsDecoderFactory:      opts.PD,
 		enableOverlappingCompaction: opts.EnableOverlappingCompaction,
 	}, nil
 }
@@ -477,7 +488,7 @@ func (c *LeveledCompactor) CompactWithBlockPopulator(dest string, dirs []string,
 
 		if b == nil {
 			var err error
-			b, err = OpenBlock(c.logger, d, c.chunkPool)
+			b, err = OpenBlock(c.logger, d, c.chunkPool, c.postingsDecoderFactory)
 			if err != nil {
 				return nil, err
 			}

tsdb/compact_test.go

@@ -1153,7 +1153,7 @@ func BenchmarkCompaction(b *testing.B) {
 			blockDirs := make([]string, 0, len(c.ranges))
 			var blocks []*Block
 			for _, r := range c.ranges {
-				block, err := OpenBlock(nil, createBlock(b, dir, genSeries(nSeries, 10, r[0], r[1])), nil)
+				block, err := OpenBlock(nil, createBlock(b, dir, genSeries(nSeries, 10, r[0], r[1])), nil, nil)
 				require.NoError(b, err)
 				blocks = append(blocks, block)
 				defer func() {
@@ -1549,7 +1549,7 @@ func TestHeadCompactionWithHistograms(t *testing.T) {
 			require.Len(t, ids, 1)
 
 			// Open the block and query it and check the histograms.
-			block, err := OpenBlock(nil, path.Join(head.opts.ChunkDirRoot, ids[0].String()), nil)
+			block, err := OpenBlock(nil, path.Join(head.opts.ChunkDirRoot, ids[0].String()), nil, nil)
 			require.NoError(t, err)
 			t.Cleanup(func() {
 				require.NoError(t, block.Close())
@@ -1911,7 +1911,7 @@ func TestCompactEmptyResultBlockWithTombstone(t *testing.T) {
 	ctx := context.Background()
 	tmpdir := t.TempDir()
 	blockDir := createBlock(t, tmpdir, genSeries(1, 1, 0, 10))
-	block, err := OpenBlock(nil, blockDir, nil)
+	block, err := OpenBlock(nil, blockDir, nil, nil)
 	require.NoError(t, err)
 	// Write tombstone covering the whole block.
 	err = block.Delete(ctx, 0, 10, labels.MustNewMatcher(labels.MatchEqual, defaultLabelName, "0"))

tsdb/db.go

@@ -91,6 +91,7 @@ func DefaultOptions() *Options {
 		EnableDelayedCompaction:     false,
 		CompactionDelayMaxPercent:   DefaultCompactionDelayMaxPercent,
 		CompactionDelay:             time.Duration(0),
+		PostingsDecoderFactory:      DefaultPostingsDecoderFactory,
 	}
 }
 
@@ -219,6 +220,10 @@ type Options struct {
 
 	// BlockChunkQuerierFunc is a function to return storage.ChunkQuerier from a BlockReader.
 	BlockChunkQuerierFunc BlockChunkQuerierFunc
+
+	// PostingsDecoderFactory allows users to customize postings decoders based on BlockMeta.
+	// By default, DefaultPostingsDecoderFactory will be used to create raw posting decoder.
+	PostingsDecoderFactory PostingsDecoderFactory
 }
 
 type NewCompactorFunc func(ctx context.Context, r prometheus.Registerer, l *slog.Logger, ranges []int64, pool chunkenc.Pool, opts *Options) (Compactor, error)
@@ -633,7 +638,7 @@ func (db *DBReadOnly) Blocks() ([]BlockReader, error) {
 		return nil, ErrClosed
 	default:
 	}
-	loadable, corrupted, err := openBlocks(db.logger, db.dir, nil, nil)
+	loadable, corrupted, err := openBlocks(db.logger, db.dir, nil, nil, DefaultPostingsDecoderFactory)
 	if err != nil {
 		return nil, err
 	}
@@ -731,7 +736,7 @@ func (db *DBReadOnly) LastBlockID() (string, error) {
 }
 
 // Block returns a block reader by given block id.
-func (db *DBReadOnly) Block(blockID string) (BlockReader, error) {
+func (db *DBReadOnly) Block(blockID string, postingsDecoderFactory PostingsDecoderFactory) (BlockReader, error) {
 	select {
 	case <-db.closed:
 		return nil, ErrClosed
@@ -743,7 +748,7 @@ func (db *DBReadOnly) Block(blockID string) (BlockReader, error) {
 		return nil, fmt.Errorf("invalid block ID %s", blockID)
 	}
 
-	block, err := OpenBlock(db.logger, filepath.Join(db.dir, blockID), nil)
+	block, err := OpenBlock(db.logger, filepath.Join(db.dir, blockID), nil, postingsDecoderFactory)
 	if err != nil {
 		return nil, err
 	}
@@ -902,6 +907,7 @@ func open(dir string, l *slog.Logger, r prometheus.Registerer, opts *Options, rn
 		db.compactor, err = NewLeveledCompactorWithOptions(ctx, r, l, rngs, db.chunkPool, LeveledCompactorOptions{
 			MaxBlockChunkSegmentSize:    opts.MaxBlockChunkSegmentSize,
 			EnableOverlappingCompaction: opts.EnableOverlappingCompaction,
+			PD:                          opts.PostingsDecoderFactory,
 		})
 	}
 	if err != nil {
@@ -1568,7 +1574,7 @@ func (db *DB) reloadBlocks() (err error) {
 	db.mtx.Lock()
 	defer db.mtx.Unlock()
 
-	loadable, corrupted, err := openBlocks(db.logger, db.dir, db.blocks, db.chunkPool)
+	loadable, corrupted, err := openBlocks(db.logger, db.dir, db.blocks, db.chunkPool, db.opts.PostingsDecoderFactory)
 	if err != nil {
 		return err
 	}
@@ -1663,7 +1669,7 @@ func (db *DB) reloadBlocks() (err error) {
 	return nil
 }
 
-func openBlocks(l *slog.Logger, dir string, loaded []*Block, chunkPool chunkenc.Pool) (blocks []*Block, corrupted map[ulid.ULID]error, err error) {
+func openBlocks(l *slog.Logger, dir string, loaded []*Block, chunkPool chunkenc.Pool, postingsDecoderFactory PostingsDecoderFactory) (blocks []*Block, corrupted map[ulid.ULID]error, err error) {
 	bDirs, err := blockDirs(dir)
 	if err != nil {
 		return nil, nil, fmt.Errorf("find blocks: %w", err)
@@ -1680,7 +1686,7 @@ func openBlocks(l *slog.Logger, dir string, loaded []*Block, chunkPool chunkenc.
 		// See if we already have the block in memory or open it otherwise.
 		block, open := getBlock(loaded, meta.ULID)
 		if !open {
-			block, err = OpenBlock(l, bDir, chunkPool)
+			block, err = OpenBlock(l, bDir, chunkPool, postingsDecoderFactory)
 			if err != nil {
 				corrupted[meta.ULID] = err
 				continue

tsdb/db_test.go

@@ -1320,7 +1320,7 @@ func TestTombstoneCleanFail(t *testing.T) {
 	totalBlocks := 2
 	for i := 0; i < totalBlocks; i++ {
 		blockDir := createBlock(t, db.Dir(), genSeries(1, 1, int64(i), int64(i)+1))
-		block, err := OpenBlock(nil, blockDir, nil)
+		block, err := OpenBlock(nil, blockDir, nil, nil)
 		require.NoError(t, err)
 		// Add some fake tombstones to trigger the compaction.
 		tomb := tombstones.NewMemTombstones()
@@ -1375,7 +1375,7 @@ func TestTombstoneCleanRetentionLimitsRace(t *testing.T) {
 			// Generate some blocks with old mint (near epoch).
 			for j := 0; j < totalBlocks; j++ {
 				blockDir := createBlock(t, dbDir, genSeries(10, 1, int64(j), int64(j)+1))
-				block, err := OpenBlock(nil, blockDir, nil)
+				block, err := OpenBlock(nil, blockDir, nil, nil)
 				require.NoError(t, err)
 				// Cover block with tombstones so it can be deleted with CleanTombstones() as well.
 				tomb := tombstones.NewMemTombstones()
@@ -1436,7 +1436,7 @@ func (c *mockCompactorFailing) Write(dest string, _ BlockReader, _, _ int64, _ *
 		return []ulid.ULID{}, errors.New("the compactor already did the maximum allowed blocks so it is time to fail")
 	}
 
-	block, err := OpenBlock(nil, createBlock(c.t, dest, genSeries(1, 1, 0, 1)), nil)
+	block, err := OpenBlock(nil, createBlock(c.t, dest, genSeries(1, 1, 0, 1)), nil, nil)
 	require.NoError(c.t, err)
 	require.NoError(c.t, block.Close()) // Close block as we won't be using anywhere.
 	c.blocks = append(c.blocks, block)
@@ -2509,13 +2509,13 @@ func TestDBReadOnly(t *testing.T) {
 	})
 	t.Run("block", func(t *testing.T) {
 		blockID := expBlock.meta.ULID.String()
-		block, err := dbReadOnly.Block(blockID)
+		block, err := dbReadOnly.Block(blockID, nil)
 		require.NoError(t, err)
 		require.Equal(t, expBlock.Meta(), block.Meta(), "block meta mismatch")
 	})
 	t.Run("invalid block ID", func(t *testing.T) {
 		blockID := "01GTDVZZF52NSWB5SXQF0P2PGF"
-		_, err := dbReadOnly.Block(blockID)
+		_, err := dbReadOnly.Block(blockID, nil)
 		require.Error(t, err)
 	})
 	t.Run("last block ID", func(t *testing.T) {
@@ -8851,7 +8851,7 @@ func TestBlockQuerierAndBlockChunkQuerier(t *testing.T) {
 		// Include blockID into series to identify which block got touched.
 		serieses := []storage.Series{storage.NewListSeries(labels.FromMap(map[string]string{"block": fmt.Sprintf("block-%d", i), labels.MetricName: "test_metric"}), []chunks.Sample{sample{t: 0, f: 1}})}
 		blockDir := createBlock(t, db.Dir(), serieses)
-		b, err := OpenBlock(db.logger, blockDir, db.chunkPool)
+		b, err := OpenBlock(db.logger, blockDir, db.chunkPool, nil)
 		require.NoError(t, err)
 
 		// Overwrite meta.json with compaction section for testing purpose.

tsdb/index/index.go

@@ -118,6 +118,8 @@ type symbolCacheEntry struct {
 
 type PostingsEncoder func(*encoding.Encbuf, []uint32) error
 
+type PostingsDecoder func(encoding.Decbuf) (int, Postings, error)
+
 // Writer implements the IndexWriter interface for the standard
 // serialization format.
 type Writer struct {
@@ -1157,17 +1159,17 @@ func (b realByteSlice) Sub(start, end int) ByteSlice {
 
 // NewReader returns a new index reader on the given byte slice. It automatically
 // handles different format versions.
-func NewReader(b ByteSlice) (*Reader, error) {
-	return newReader(b, io.NopCloser(nil))
+func NewReader(b ByteSlice, decoder PostingsDecoder) (*Reader, error) {
+	return newReader(b, io.NopCloser(nil), decoder)
 }
 
 // NewFileReader returns a new index reader against the given index file.
-func NewFileReader(path string) (*Reader, error) {
+func NewFileReader(path string, decoder PostingsDecoder) (*Reader, error) {
 	f, err := fileutil.OpenMmapFile(path)
 	if err != nil {
 		return nil, err
 	}
-	r, err := newReader(realByteSlice(f.Bytes()), f)
+	r, err := newReader(realByteSlice(f.Bytes()), f, decoder)
 	if err != nil {
 		return nil, tsdb_errors.NewMulti(
 			err,
@@ -1178,7 +1180,7 @@ func NewFileReader(path string) (*Reader, error) {
 	return r, nil
 }
 
-func newReader(b ByteSlice, c io.Closer) (*Reader, error) {
+func newReader(b ByteSlice, c io.Closer, postingsDecoder PostingsDecoder) (*Reader, error) {
 	r := &Reader{
 		b:        b,
 		c:        c,
@@ -1277,7 +1279,7 @@ func newReader(b ByteSlice, c io.Closer) (*Reader, error) {
 		r.nameSymbols[off] = k
 	}
 
-	r.dec = &Decoder{LookupSymbol: r.lookupSymbol}
+	r.dec = &Decoder{LookupSymbol: r.lookupSymbol, DecodePostings: postingsDecoder}
 
 	return r, nil
 }
@@ -1706,7 +1708,7 @@ func (r *Reader) Postings(ctx context.Context, name string, values ...string) (P
 			}
 			// Read from the postings table.
 			d := encoding.NewDecbufAt(r.b, int(postingsOff), castagnoliTable)
-			_, p, err := r.dec.Postings(d.Get())
+			_, p, err := r.dec.DecodePostings(d)
 			if err != nil {
 				return nil, fmt.Errorf("decode postings: %w", err)
 			}
@@ -1749,7 +1751,7 @@ func (r *Reader) Postings(ctx context.Context, name string, values ...string) (P
 				if val == value {
 					// Read from the postings table.
 					d2 := encoding.NewDecbufAt(r.b, int(postingsOff), castagnoliTable)
-					_, p, err := r.dec.Postings(d2.Get())
+					_, p, err := r.dec.DecodePostings(d2)
 					if err != nil {
 						return false, fmt.Errorf("decode postings: %w", err)
 					}
@@ -1790,7 +1792,7 @@ func (r *Reader) PostingsForLabelMatching(ctx context.Context, name string, matc
 		if match(val) {
 			// We want this postings iterator since the value is a match
 			postingsDec := encoding.NewDecbufAt(r.b, int(postingsOff), castagnoliTable)
-			_, p, err := r.dec.PostingsFromDecbuf(postingsDec)
+			_, p, err := r.dec.DecodePostings(postingsDec)
 			if err != nil {
 				return false, fmt.Errorf("decode postings: %w", err)
 			}
@@ -1823,7 +1825,7 @@ func (r *Reader) postingsForLabelMatchingV1(ctx context.Context, name string, ma
 
 		// Read from the postings table.
 		d := encoding.NewDecbufAt(r.b, int(offset), castagnoliTable)
-		_, p, err := r.dec.PostingsFromDecbuf(d)
+		_, p, err := r.dec.DecodePostings(d)
 		if err != nil {
 			return ErrPostings(fmt.Errorf("decode postings: %w", err))
 		}
@@ -1918,17 +1920,12 @@ func (s stringListIter) Err() error { return nil }
 // It currently does not contain decoding methods for all entry types but can be extended
 // by them if there's demand.
 type Decoder struct {
-	LookupSymbol func(context.Context, uint32) (string, error)
-}
-
-// Postings returns a postings list for b and its number of elements.
-func (dec *Decoder) Postings(b []byte) (int, Postings, error) {
-	d := encoding.Decbuf{B: b}
-	return dec.PostingsFromDecbuf(d)
+	LookupSymbol   func(context.Context, uint32) (string, error)
+	DecodePostings PostingsDecoder
 }
 
-// PostingsFromDecbuf returns a postings list for d and its number of elements.
-func (dec *Decoder) PostingsFromDecbuf(d encoding.Decbuf) (int, Postings, error) {
+// DecodePostingsRaw returns a postings list for d and its number of elements.
+func DecodePostingsRaw(d encoding.Decbuf) (int, Postings, error) {
 	n := d.Be32int()
 	l := d.Get()
 	if d.Err() != nil {

tsdb/index/index_test.go

@@ -146,7 +146,7 @@ func TestIndexRW_Create_Open(t *testing.T) {
 	require.NoError(t, err)
 	require.NoError(t, iw.Close())
 
-	ir, err := NewFileReader(fn)
+	ir, err := NewFileReader(fn, DecodePostingsRaw)
 	require.NoError(t, err)
 	require.NoError(t, ir.Close())
 
@@ -157,7 +157,7 @@ func TestIndexRW_Create_Open(t *testing.T) {
 	require.NoError(t, err)
 	f.Close()
 
-	_, err = NewFileReader(dir)
+	_, err = NewFileReader(dir, DecodePostingsRaw)
 	require.Error(t, err)
 }
 
@@ -218,7 +218,7 @@ func TestIndexRW_Postings(t *testing.T) {
 	}, labelIndices)
 
 	t.Run("ShardedPostings()", func(t *testing.T) {
-		ir, err := NewFileReader(fn)
+		ir, err := NewFileReader(fn, DecodePostingsRaw)
 		require.NoError(t, err)
 		t.Cleanup(func() {
 			require.NoError(t, ir.Close())
@@ -469,7 +469,7 @@ func TestDecbufUvarintWithInvalidBuffer(t *testing.T) {
 func TestReaderWithInvalidBuffer(t *testing.T) {
 	b := realByteSlice([]byte{0x81, 0x81, 0x81, 0x81, 0x81, 0x81})
 
-	_, err := NewReader(b)
+	_, err := NewReader(b, DecodePostingsRaw)
 	require.Error(t, err)
 }
 
@@ -481,7 +481,7 @@ func TestNewFileReaderErrorNoOpenFiles(t *testing.T) {
 	err := os.WriteFile(idxName, []byte("corrupted contents"), 0o666)
 	require.NoError(t, err)
 
-	_, err = NewFileReader(idxName)
+	_, err = NewFileReader(idxName, DecodePostingsRaw)
 	require.Error(t, err)
 
 	// dir.Close will fail on Win if idxName fd is not closed on error path.
@@ -560,7 +560,8 @@ func BenchmarkReader_ShardedPostings(b *testing.B) {
 }
 
 func TestDecoder_Postings_WrongInput(t *testing.T) {
-	_, _, err := (&Decoder{}).Postings([]byte("the cake is a lie"))
+	d := encoding.Decbuf{B: []byte("the cake is a lie")}
+	_, _, err := (&Decoder{DecodePostings: DecodePostingsRaw}).DecodePostings(d)
 	require.Error(t, err)
 }
 
@@ -690,7 +691,7 @@ func createFileReader(ctx context.Context, tb testing.TB, input indexWriterSerie
 	}
 	require.NoError(tb, iw.Close())
 
-	ir, err := NewFileReader(fn)
+	ir, err := NewFileReader(fn, DecodePostingsRaw)
 	require.NoError(tb, err)
 	tb.Cleanup(func() {
 		require.NoError(tb, ir.Close())

tsdb/querier_bench_test.go

@@ -75,7 +75,7 @@ func BenchmarkQuerier(b *testing.B) {
 
 	b.Run("Block", func(b *testing.B) {
 		blockdir := createBlockFromHead(b, b.TempDir(), h)
-		block, err := OpenBlock(nil, blockdir, nil)
+		block, err := OpenBlock(nil, blockdir, nil, nil)
 		require.NoError(b, err)
 		defer func() {
 			require.NoError(b, block.Close())
@@ -315,7 +315,7 @@ func BenchmarkQuerierSelect(b *testing.B) {
 		tmpdir := b.TempDir()
 
 		blockdir := createBlockFromHead(b, tmpdir, h)
-		block, err := OpenBlock(nil, blockdir, nil)
+		block, err := OpenBlock(nil, blockdir, nil, nil)
 		require.NoError(b, err)
 		defer func() {
 			require.NoError(b, block.Close())

tsdb/querier_test.go

@@ -2443,7 +2443,7 @@ func BenchmarkQueryIterator(b *testing.B) {
 					} else {
 						generatedSeries = populateSeries(prefilledLabels, mint, maxt)
 					}
-					block, err := OpenBlock(nil, createBlock(b, dir, generatedSeries), nil)
+					block, err := OpenBlock(nil, createBlock(b, dir, generatedSeries), nil, nil)
 					require.NoError(b, err)
 					blocks = append(blocks, block)
 					defer block.Close()
@@ -2506,7 +2506,7 @@ func BenchmarkQuerySeek(b *testing.B) {
 					} else {
 						generatedSeries = populateSeries(prefilledLabels, mint, maxt)
 					}
-					block, err := OpenBlock(nil, createBlock(b, dir, generatedSeries), nil)
+					block, err := OpenBlock(nil, createBlock(b, dir, generatedSeries), nil, nil)
 					require.NoError(b, err)
 					blocks = append(blocks, block)
 					defer block.Close()
@@ -2641,7 +2641,7 @@ func BenchmarkSetMatcher(b *testing.B) {
 			} else {
 				generatedSeries = populateSeries(prefilledLabels, mint, maxt)
 			}
-			block, err := OpenBlock(nil, createBlock(b, dir, generatedSeries), nil)
+			block, err := OpenBlock(nil, createBlock(b, dir, generatedSeries), nil, nil)
 			require.NoError(b, err)
 			blocks = append(blocks, block)
 			defer block.Close()
@@ -3209,7 +3209,7 @@ func BenchmarkQueries(b *testing.B) {
 
 				qs := make([]storage.Querier, 0, 10)
 				for x := 0; x <= 10; x++ {
-					block, err := OpenBlock(nil, createBlock(b, dir, series), nil)
+					block, err := OpenBlock(nil, createBlock(b, dir, series), nil, nil)
 					require.NoError(b, err)
 					q, err := NewBlockQuerier(block, 1, nSamples)
 					require.NoError(b, err)
@@ -3792,7 +3792,7 @@ func (m mockReaderOfLabels) Symbols() index.StringIter {
 // https://github.com/prometheus/prometheus/issues/14723, when one of the queriers (blockQuerier in this case)
 // alters the passed matchers.
 func TestMergeQuerierConcurrentSelectMatchers(t *testing.T) {
-	block, err := OpenBlock(nil, createBlock(t, t.TempDir(), genSeries(1, 1, 0, 1)), nil)
+	block, err := OpenBlock(nil, createBlock(t, t.TempDir(), genSeries(1, 1, 0, 1)), nil, nil)
 	require.NoError(t, err)
 	defer func() {
 		require.NoError(t, block.Close())

tsdb/repair_test.go

@@ -79,7 +79,7 @@ func TestRepairBadIndexVersion(t *testing.T) {
 	require.NoError(t, os.MkdirAll(filepath.Join(tmpDbDir, "chunks"), 0o777))
 
 	// Read current index to check integrity.
-	r, err := index.NewFileReader(filepath.Join(tmpDbDir, indexFilename))
+	r, err := index.NewFileReader(filepath.Join(tmpDbDir, indexFilename), index.DecodePostingsRaw)
 	require.NoError(t, err)
 	p, err := r.Postings(ctx, "b", "1")
 	require.NoError(t, err)
@@ -97,7 +97,7 @@ func TestRepairBadIndexVersion(t *testing.T) {
 	require.NoError(t, err)
 	db.Close()
 
-	r, err = index.NewFileReader(filepath.Join(tmpDbDir, indexFilename))
+	r, err = index.NewFileReader(filepath.Join(tmpDbDir, indexFilename), index.DecodePostingsRaw)
 	require.NoError(t, err)
 	defer r.Close()
 	p, err = r.Postings(ctx, "b", "1")