[#754] blobstor: Estimate compressability

Now it is possible to enable compressability estimation.
If data is likely uncompressable, it should reduce CPU time and memory.

Signed-off-by: Dmitrii Stepanov <d.stepanov@yadro.com>

pkg/local_object_storage/blobstor/compression/compress.go

@@ -5,6 +5,7 @@ import (
 	"strings"
 
 	objectSDK "git.frostfs.info/TrueCloudLab/frostfs-sdk-go/object"
+	"github.com/klauspost/compress"
 	"github.com/klauspost/compress/zstd"
 )
 
@@ -13,6 +14,9 @@ type Config struct {
 	Enabled                    bool
 	UncompressableContentTypes []string
 
+	UseCompressEstimation       bool
+	CompressEstimationThreshold float64
+
 	encoder *zstd.Encoder
 	decoder *zstd.Decoder
 }
@@ -82,6 +86,17 @@ func (c *Config) Compress(data []byte) []byte {
 	if c == nil || !c.Enabled {
 		return data
 	}
+	if c.UseCompressEstimation {
+		estimated := compress.Estimate(data)
+		if estimated >= c.CompressEstimationThreshold {
+			return c.compress(data)
+		}
+		return data
+	}
+	return c.compress(data)
+}
+
+func (c *Config) compress(data []byte) []byte {
 	maxSize := c.encoder.MaxEncodedSize(len(data))
 	compressed := c.encoder.EncodeAll(data, make([]byte, 0, maxSize))
 	if len(data) < len(compressed) {