sstable: add adaptive compression

Add adaptive compression with zstd and snappy. zstd copmression is
probed with exponential backoff when compression ratios are not
better than 50%.

Author: EdwardX29

db.go

@@ -2078,6 +2078,7 @@ func (d *DB) Metrics() *Metrics {
 		metrics.Table.CompressedCountSnappy += int64(compressionTypes.snappy)
 		metrics.Table.CompressedCountZstd += int64(compressionTypes.zstd)
 		metrics.Table.CompressedCountMinlz += int64(compressionTypes.minlz)
+		metrics.Table.CompressedCountAdaptive += int64(compressionTypes.adaptive)
 		metrics.Table.CompressedCountNone += int64(compressionTypes.none)
 	}
 

metrics.go

@@ -294,6 +294,8 @@ type Metrics struct {
 		CompressedCountMinlz int64
 		// The number of sstables that are uncompressed.
 		CompressedCountNone int64
+		// The number of sstables that are compressed with adaptive.
+		CompressedCountAdaptive int64
 
 		// Local file sizes.
 		Local struct {
@@ -696,6 +698,9 @@ func (m *Metrics) SafeFormat(w redact.SafePrinter, _ rune) {
 	if count := m.Table.CompressedCountMinlz; count > 0 {
 		w.Printf(" minlz: %d", redact.Safe(count))
 	}
+	if count := m.Table.CompressedCountAdaptive; count > 0 {
+		w.Printf(" adaptive: %d", redact.Safe(count))
+	}
 	if count := m.Table.CompressedCountNone; count > 0 {
 		w.Printf(" none: %d", redact.Safe(count))
 	}

options.go

@@ -45,11 +45,12 @@ type Compression = block.Compression
 
 // Exported Compression constants.
 const (
-	DefaultCompression = block.DefaultCompression
-	NoCompression      = block.NoCompression
-	SnappyCompression  = block.SnappyCompression
-	ZstdCompression    = block.ZstdCompression
-	MinlzCompression   = block.MinlzCompression
+	DefaultCompression  = block.DefaultCompression
+	NoCompression       = block.NoCompression
+	SnappyCompression   = block.SnappyCompression
+	ZstdCompression     = block.ZstdCompression
+	MinlzCompression    = block.MinlzCompression
+	AdaptiveCompression = block.AdaptiveCompression
 )
 
 // FilterType exports the base.FilterType type.
@@ -1952,6 +1953,8 @@ func (o *Options) Parse(s string, hooks *ParseHooks) error {
 					l.Compression = func() Compression { return ZstdCompression }
 				case "Minlz":
 					l.Compression = func() Compression { return MinlzCompression }
+				case "Adaptive":
+					l.Compression = func() Compression { return AdaptiveCompression }
 				default:
 					return errors.Errorf("pebble: unknown compression: %q", errors.Safe(value))
 				}

sstable/block/compression.go

@@ -26,6 +26,10 @@ const (
 	SnappyCompression
 	ZstdCompression
 	MinlzCompression
+	// AdaptiveCompression dynamically chooses between snappy and zstd
+	// based on recent compression effectiveness. See comment for adaptiveCompressor
+	// for more details.
+	AdaptiveCompression
 	NCompression
 )
 
@@ -43,6 +47,8 @@ func (c Compression) String() string {
 		return "ZSTD"
 	case MinlzCompression:
 		return "Minlz"
+	case AdaptiveCompression:
+		return "Adaptive"
 	default:
 		return "Unknown"
 	}
@@ -62,6 +68,8 @@ func CompressionFromString(s string) Compression {
 		return ZstdCompression
 	case "Minlz":
 		return MinlzCompression
+	case "Adaptive":
+		return AdaptiveCompression
 	default:
 		return DefaultCompression
 	}

sstable/block/compressor.go

@@ -2,6 +2,7 @@ package block
 
 import (
 	"encoding/binary"
+	"sync"
 
 	"github.com/cockroachdb/errors"
 	"github.com/cockroachdb/pebble/internal/base"
@@ -21,9 +22,28 @@ type noopCompressor struct{}
 type snappyCompressor struct{}
 type minlzCompressor struct{}
 
+// adaptiveCompressor dynamically switches between snappy and zstd
+// compression. It prefers using zstd because of its potential for
+// high compression ratios. However, if zstd does not achieve a good
+// compression ratio, we apply exponential backoff before trying zstd again.
+// If the compression ratio is high (50% or better), we continue using zstd.
+type adaptiveCompressor struct {
+	// timeTilTry is the number of operations to wait before
+	// attempting zstd compression again after a poor result.
+	timeTilTry int
+
+	// zstdBackoffStep is how much we increase timeTilTry
+	// each time zstd compression fails to achieve at least
+	// a 50% compression ratio.
+	zstdBackoffStep int
+
+	zstdCompressor Compressor
+}
+
 var _ Compressor = noopCompressor{}
 var _ Compressor = snappyCompressor{}
 var _ Compressor = minlzCompressor{}
+var _ Compressor = (*adaptiveCompressor)(nil)
 
 func (noopCompressor) Compress(dst, src []byte) (CompressionIndicator, []byte) {
 	dst = append(dst[:0], src...)
@@ -63,11 +83,56 @@ func GetCompressor(c Compression) Compressor {
 		return getZstdCompressor()
 	case MinlzCompression:
 		return minlzCompressor{}
+	case AdaptiveCompression:
+		return adaptiveCompressorPool.Get().(*adaptiveCompressor)
 	default:
 		panic("Invalid compression type.")
 	}
 }
 
+var adaptiveCompressorPool = sync.Pool{
+	New: func() any {
+		return &adaptiveCompressor{zstdBackoffStep: 1, zstdCompressor: getZstdCompressor()}
+	},
+}
+
+func (a *adaptiveCompressor) Compress(dst, src []byte) (CompressionIndicator, []byte) {
+	var algo CompressionIndicator
+	var compressedBuf []byte
+	if a.timeTilTry == 0 {
+		z := a.zstdCompressor
+		algo, compressedBuf = z.Compress(dst, src)
+		// Perform a backoff if zstd compression ratio wasn't better than 50%.
+		if 10*len(compressedBuf) >= 5*len(src) {
+			a.increaseBackoff()
+		} else {
+			a.resetBackoff()
+		}
+	} else {
+		// Use Snappy
+		algo, compressedBuf = (snappyCompressor{}).Compress(dst, src)
+	}
+	a.timeTilTry--
+	return algo, compressedBuf
+}
+
+func (a *adaptiveCompressor) Close() {
+	a.timeTilTry = 0
+	a.zstdBackoffStep = 1
+	adaptiveCompressorPool.Put(a)
+}
+
+// Exponential backoff for zstd
+func (a *adaptiveCompressor) increaseBackoff() {
+	a.zstdBackoffStep *= 2
+	a.timeTilTry += a.zstdBackoffStep
+}
+
+func (a *adaptiveCompressor) resetBackoff() {
+	a.zstdBackoffStep = 1
+	a.timeTilTry = 1
+}
+
 type Decompressor interface {
 	// DecompressInto decompresses compressed into buf. The buf slice must have the
 	// exact size as the decompressed value. Callers may use DecompressedLen to

table_stats.go

@@ -1042,7 +1042,7 @@ var compressionTypeAnnotator = manifest.Annotator[compressionTypes]{
 type compressionTypeAggregator struct{}
 
 type compressionTypes struct {
-	snappy, zstd, minlz, none, unknown uint64
+	snappy, zstd, minlz, adaptive, none, unknown uint64
 }
 
 func (a compressionTypeAggregator) Zero(dst *compressionTypes) *compressionTypes {
@@ -1063,6 +1063,8 @@ func (a compressionTypeAggregator) Accumulate(
 		dst.zstd++
 	case MinlzCompression:
 		dst.minlz++
+	case AdaptiveCompression:
+		dst.adaptive++
 	case NoCompression:
 		dst.none++
 	default:
@@ -1077,6 +1079,7 @@ func (a compressionTypeAggregator) Merge(
 	dst.snappy += src.snappy
 	dst.zstd += src.zstd
 	dst.minlz += src.minlz
+	dst.adaptive += src.adaptive
 	dst.none += src.none
 	dst.unknown += src.unknown
 	return dst