Seems compress rate alway same for level1 to level9

[july2993]

test code:

package lz4

import (
	"fmt"
	"io"
	"os"

	"github.com/pierrec/lz4/v4"
	"github.com/spf13/cobra"
)

func NewLZ4Command() *cobra.Command {
	var decompress bool
	var level int
	var block int

	command := cobra.Command{
		Use: "lz4 [arg] [input] [output]",
		RunE: func(cmd *cobra.Command, args []string) error {
			if len(args) <= 0 {
				return cmd.Usage()
			}

			input := args[0]
			var output string
			if len(args) >= 2 {
				output = args[1]
			}

			if decompress {
				return fmt.Errorf("unimplemented")
			}

			// start handle compress
			if output == "" {
				output = input + ".lz4"
			}

			infile, err := os.Open(input)
			if err != nil {
				return err
			}
			defer infile.Close()

			outfile, err := os.Create(output)
			if err != nil {
				return err
			}

			zw := lz4.NewWriter(outfile)

			// lz4.ConcurrencyOption(concurrency),
			// lz4.BlockChecksumOption(blockChecksum),
			// lz4.ChecksumOption(streamChecksum),

			var options []lz4.Option
			if level > 0 {
				clv, err := toLevel(level)
				if err != nil {
					return err
				}
				op := lz4.CompressionLevelOption(clv)
				options = append(options, op)
			}

			if block > 0 {
				cblock, err := toBlockSize(block)
				if err != nil {
					return err
				}
				op := lz4.BlockSizeOption(cblock)
				options = append(options, op)
			}

			if len(options) > 0 {
				err = zw.Apply(options...)
				if err != nil {
					return err
				}
			}

			_, err = io.Copy(zw, infile)
			if err != nil {
				return fmt.Errorf("failed to compress")
			}

			err = zw.Close()
			if err != nil {
				return fmt.Errorf("failed close lz4 writer: %w", err)
			}
			err = outfile.Close()
			if err != nil {
				return fmt.Errorf("failed close file: %w", err)
			}

			outStat, err := os.Stat(output)
			if err != nil {
				return fmt.Errorf("failed to stat %q: %w", output, err)
			}

			inStat, err := infile.Stat()
			if err != nil {
				return err
			}

			fmt.Printf("Compress: %0.2f\n", float64(outStat.Size())*100.0/float64(inStat.Size()))

			return nil
		},
	}

	command.Flags().BoolVarP(&decompress, "decompress", "d", false, "decompression (default for .lz4 extension)")
	command.Flags().IntVarP(&level, "level", "i", 0, "level 1-9")
	command.Flags().IntVarP(&block, "block", "B", 0, "block 4-7")

	return &command
}

func toLevel(lv int) (lz4.CompressionLevel, error) {
	if lv > 9 {
		return 0, fmt.Errorf("unsupported level: %v", lv)
	}

	var clv uint32 = 1 << (8 + lv)
	if lv == 9 && lz4.CompressionLevel(clv) != lz4.Level9 {
		panic("..")
	}

	fmt.Println("level lz4.CompressionLevel: ", lz4.CompressionLevel(clv))

	return lz4.CompressionLevel(clv), nil
}

func toBlockSize(block int) (lz4.BlockSize, error) {
	switch block {
	case 4:
		return lz4.Block64Kb, nil
	case 5:
		return lz4.Block256Kb, nil
	case 6:
		return lz4.Block1Mb, nil
	case 7:
		return lz4.Block4Mb, nil
	default:
		return 0, fmt.Errorf("unsupported block size: %v", block)
	}
}

I test on some file with default value and level 1 - 9:

#! /bin/bash

file=./20230628171044.xml
# file=./binlog.bk

rm $file.lz4
go run main.go lz4 -B 4 $file

for (( i=1; i < 10;i++ )); do
  rm $file.lz4
  go run main.go lz4 -i $i -B 4 $file
done

The compress rate seems always same for level 1 to level 9

Compress: 7.66
level lz4.CompressionLevel:  Level1
Compress: 6.44
level lz4.CompressionLevel:  Level2
Compress: 6.44
level lz4.CompressionLevel:  Level3
Compress: 6.44
level lz4.CompressionLevel:  Level4
Compress: 6.44
level lz4.CompressionLevel:  Level5
Compress: 6.44
level lz4.CompressionLevel:  Level6
Compress: 6.44
level lz4.CompressionLevel:  Level7
Compress: 6.44
level lz4.CompressionLevel:  Level8
Compress: 6.44
level lz4.CompressionLevel:  Level9
Compress: 6.44