compression: add Compressor.Algorithm() convenience method

Author: RaduBerinde

internal/compression/compression.go

@@ -72,6 +72,9 @@ var (
 // Compressor is an interface for compressing data. An instance is associated
 // with a specific Setting.
 type Compressor interface {
+	// Algorithm returns the algorithm used by this Compressor.
+	Algorithm() Algorithm
+
 	// Compress a block, appending the compressed data to dst[:0].
 	Compress(dst, src []byte) []byte
 

internal/compression/minlz.go

@@ -16,6 +16,8 @@ type minlzCompressor struct {
 
 var _ Compressor = (*minlzCompressor)(nil)
 
+func (c *minlzCompressor) Algorithm() Algorithm { return MinLZ }
+
 func (c *minlzCompressor) Compress(dst, src []byte) []byte {
 	// MinLZ cannot encode blocks greater than 8MB. Fall back to Snappy in those
 	// cases. Note that MinLZ can decode the Snappy compressed block.

internal/compression/noop.go

@@ -8,6 +8,7 @@ type noopCompressor struct{}
 
 var _ Compressor = noopCompressor{}
 
+func (noopCompressor) Algorithm() Algorithm { return NoCompression }
 func (noopCompressor) Compress(dst, src []byte) []byte {
 	return append(dst[:0], src...)
 }

internal/compression/snappy.go

@@ -14,6 +14,8 @@ type snappyCompressor struct{}
 
 var _ Compressor = snappyCompressor{}
 
+func (snappyCompressor) Algorithm() Algorithm { return SnappyAlgorithm }
+
 func (snappyCompressor) Compress(dst, src []byte) []byte {
 	dst = dst[:cap(dst):cap(dst)]
 	return snappy.Encode(dst, src)

internal/compression/zstd_cgo.go

@@ -39,6 +39,8 @@ var zstdCompressorPool = sync.Pool{
 // relies on CGo.
 const UseStandardZstdLib = true
 
+func (z *zstdCompressor) Algorithm() Algorithm { return Zstd }
+
 func (z *zstdCompressor) Compress(compressedBuf []byte, b []byte) []byte {
 	if len(compressedBuf) < binary.MaxVarintLen64 {
 		compressedBuf = append(compressedBuf, make([]byte, binary.MaxVarintLen64-len(compressedBuf))...)

internal/compression/zstd_nocgo.go

@@ -34,6 +34,8 @@ func getZstdCompressor(level int) *zstdCompressor {
 // relies on CGo.
 const UseStandardZstdLib = false
 
+func (z *zstdCompressor) Algorithm() Algorithm { return Zstd }
+
 func (z *zstdCompressor) Compress(compressedBuf, b []byte) []byte {
 	if len(compressedBuf) < binary.MaxVarintLen64 {
 		compressedBuf = append(compressedBuf, make([]byte, binary.MaxVarintLen64-len(compressedBuf))...)

sstable/block/compressor.go

@@ -48,10 +48,8 @@ func (c *Compressor) Close() {
 //
 // In addition to the buffer, returns the algorithm that was used.
 func (c *Compressor) Compress(dst, src []byte, kind Kind) (CompressionIndicator, []byte) {
-	setting := c.profile.DataBlocks
 	compressor := c.dataBlocksCompressor
 	if kind != blockkind.SSTableData && kind != blockkind.SSTableValue && kind != blockkind.BlobValue {
-		setting = c.profile.OtherBlocks
 		compressor = c.otherBlocksCompressor
 	}
 	out := compressor.Compress(dst, src)
@@ -62,11 +60,12 @@ func (c *Compressor) Compress(dst, src []byte, kind Kind) (CompressionIndicator,
 	//   after * 100
 	//   -----------  >  100 - MinReductionPercent
 	//      before
-	if setting.Algorithm != compression.NoCompression &&
+	algorithm := compressor.Algorithm()
+	if algorithm != compression.NoCompression &&
 		int64(len(out))*100 > int64(len(src))*int64(100-c.profile.MinReductionPercent) {
 		return NoCompressionIndicator, append(out[:0], src...)
 	}
-	return compressionIndicatorFromAlgorithm(setting.Algorithm), out
+	return compressionIndicatorFromAlgorithm(algorithm), out
 }
 
 // NoopCompressor is a Compressor that does not compress data. It does not have