gzip: Use sync.pool

This commit uses a sync.Pool for botht he gzip writer and reader
so that we reduce the number of allocations and time GC takes as previously
every mutation that required to be gzipped would make a call to newWriter
and allocate a new object. This in turn spent a lot of time and created
extra objects on the heap that were un needed which drove up GC time

internal/staging/stage/gzip.go

@@ -20,6 +20,7 @@ import (
 	"bytes"
 	"compress/gzip"
 	"io"
+	"sync"
 
 	"github.com/pkg/errors"
 )
@@ -29,14 +30,31 @@ import (
 // with some benefit for tables that have very wide rows or values.
 const gzipMinSize = 1024
 
+// Create a sync.Pool for gzip.Writer instances
+var gzipWriterPool = sync.Pool{
+	New: func() interface{} {
+		return gzip.NewWriter(nil)
+	},
+}
+
+// Create a sync.Pool for gzip.Reader instances
+var gzipReaderPool = sync.Pool{
+	New: func() interface{} {
+		return &gzip.Reader{}
+	},
+}
+
 // maybeGZip compresses the given data if it is larger than gzipMinSize.
 func maybeGZip(data []byte) ([]byte, error) {
 	if len(data) <= gzipMinSize {
 		return data, nil
 	}
 
 	var buf bytes.Buffer
-	gzWriter := gzip.NewWriter(&buf)
+	gzWriter := gzipWriterPool.Get().(*gzip.Writer)
+	gzWriter.Reset(&buf)
+	defer gzipWriterPool.Put(gzWriter)
+
 	if _, err := gzWriter.Write(data); err != nil {
 		return nil, errors.WithStack(err)
 	}
@@ -55,9 +73,13 @@ func maybeGunzip(data []byte) ([]byte, error) {
 	if len(data) < 2 || data[0] != 0x1f || data[1] != 0x8b {
 		return data, nil
 	}
-	r, err := gzip.NewReader(bytes.NewReader(data))
+
+	gzReader := gzipReaderPool.Get().(*gzip.Reader)
+	defer gzipReaderPool.Put(gzReader)
+	err := gzReader.Reset(bytes.NewReader(data))
 	if err != nil {
 		return nil, errors.WithStack(err)
 	}
-	return io.ReadAll(r)
+	defer gzReader.Close()
+	return io.ReadAll(gzReader)
 }