add sync pool for gzip 1-9 (IBM#1560)

compress.go

@@ -22,6 +22,87 @@ var (
 			return gzip.NewWriter(nil)
 		},
 	}
+	gzipWriterPoolForCompressionLevel1 = sync.Pool{
+		New: func() interface{} {
+			gz, err := gzip.NewWriterLevel(nil, 1)
+			if err != nil {
+				panic(err)
+			}
+			return gz
+		},
+	}
+	gzipWriterPoolForCompressionLevel2 = sync.Pool{
+		New: func() interface{} {
+			gz, err := gzip.NewWriterLevel(nil, 2)
+			if err != nil {
+				panic(err)
+			}
+			return gz
+		},
+	}
+	gzipWriterPoolForCompressionLevel3 = sync.Pool{
+		New: func() interface{} {
+			gz, err := gzip.NewWriterLevel(nil, 3)
+			if err != nil {
+				panic(err)
+			}
+			return gz
+		},
+	}
+	gzipWriterPoolForCompressionLevel4 = sync.Pool{
+		New: func() interface{} {
+			gz, err := gzip.NewWriterLevel(nil, 4)
+			if err != nil {
+				panic(err)
+			}
+			return gz
+		},
+	}
+	gzipWriterPoolForCompressionLevel5 = sync.Pool{
+		New: func() interface{} {
+			gz, err := gzip.NewWriterLevel(nil, 5)
+			if err != nil {
+				panic(err)
+			}
+			return gz
+		},
+	}
+	gzipWriterPoolForCompressionLevel6 = sync.Pool{
+		New: func() interface{} {
+			gz, err := gzip.NewWriterLevel(nil, 6)
+			if err != nil {
+				panic(err)
+			}
+			return gz
+		},
+	}
+	gzipWriterPoolForCompressionLevel7 = sync.Pool{
+		New: func() interface{} {
+			gz, err := gzip.NewWriterLevel(nil, 7)
+			if err != nil {
+				panic(err)
+			}
+			return gz
+		},
+	}
+	gzipWriterPoolForCompressionLevel8 = sync.Pool{
+		New: func() interface{} {
+			gz, err := gzip.NewWriterLevel(nil, 8)
+			if err != nil {
+				panic(err)
+			}
+			return gz
+		},
+	}
+	gzipWriterPoolForCompressionLevel9 = sync.Pool{
+		New: func() interface{} {
+			gz, err := gzip.NewWriterLevel(nil, 9)
+			if err != nil {
+				panic(err)
+			}
+			return gz
+		},
+	}
 )
 
 func compress(cc CompressionCodec, level int, data []byte) ([]byte, error) {
@@ -34,15 +115,53 @@ func compress(cc CompressionCodec, level int, data []byte) ([]byte, error) {
 			buf    bytes.Buffer
 			writer *gzip.Writer
 		)
-		if level != CompressionLevelDefault {
+
+		switch level {
+		case CompressionLevelDefault:
+			writer = gzipWriterPool.Get().(*gzip.Writer)
+			defer gzipWriterPool.Put(writer)
+			writer.Reset(&buf)
+		case 1:
+			writer = gzipWriterPoolForCompressionLevel1.Get().(*gzip.Writer)
+			defer gzipWriterPoolForCompressionLevel1.Put(writer)
+			writer.Reset(&buf)
+		case 2:
+			writer = gzipWriterPoolForCompressionLevel2.Get().(*gzip.Writer)
+			defer gzipWriterPoolForCompressionLevel2.Put(writer)
+			writer.Reset(&buf)
+		case 3:
+			writer = gzipWriterPoolForCompressionLevel3.Get().(*gzip.Writer)
+			defer gzipWriterPoolForCompressionLevel3.Put(writer)
+			writer.Reset(&buf)
+		case 4:
+			writer = gzipWriterPoolForCompressionLevel4.Get().(*gzip.Writer)
+			defer gzipWriterPoolForCompressionLevel4.Put(writer)
+			writer.Reset(&buf)
+		case 5:
+			writer = gzipWriterPoolForCompressionLevel5.Get().(*gzip.Writer)
+			defer gzipWriterPoolForCompressionLevel5.Put(writer)
+			writer.Reset(&buf)
+		case 6:
+			writer = gzipWriterPoolForCompressionLevel6.Get().(*gzip.Writer)
+			defer gzipWriterPoolForCompressionLevel6.Put(writer)
+			writer.Reset(&buf)
+		case 7:
+			writer = gzipWriterPoolForCompressionLevel7.Get().(*gzip.Writer)
+			defer gzipWriterPoolForCompressionLevel7.Put(writer)
+			writer.Reset(&buf)
+		case 8:
+			writer = gzipWriterPoolForCompressionLevel8.Get().(*gzip.Writer)
+			defer gzipWriterPoolForCompressionLevel8.Put(writer)
+			writer.Reset(&buf)
+		case 9:
+			writer = gzipWriterPoolForCompressionLevel9.Get().(*gzip.Writer)
+			defer gzipWriterPoolForCompressionLevel9.Put(writer)
+			writer.Reset(&buf)
+		default:
 			writer, err = gzip.NewWriterLevel(&buf, level)
 			if err != nil {
 				return nil, err
 			}
-		} else {
-			writer = gzipWriterPool.Get().(*gzip.Writer)
-			defer gzipWriterPool.Put(writer)
-			writer.Reset(&buf)
 		}
 		if _, err := writer.Write(data); err != nil {
 			return nil, err