zlib is often used in PHP projects for cache compression. Symfony's DeflateMarshaller implementation is an example. The speed of compression plays an important role in the performance of the web application. Based on this, I decided to check what compression level is the most optimal.
The following results are obtained with the script benchmarking gzdeflate and gzinflate functions of the php-zlib extension. The benchmark has been launched with PHP 7.4.33 on Amazon EC2 c5.xlarge instance. C5 instances are built on 3.0 GHz Intel Xeon Scalable (Skylake) processors, and have the potential to run at speeds up to 3.5 Ghz using Intel Turbo Boost Technology.
| Compression level | Compression Speed, MB/s | Decompression Speed, MB/s | Compression Ratio | Space Saving, % | Ratio / Time |
|---|---|---|---|---|---|
| 1 | 137.16 | 64.41 | 7.4 | 86.6 | 2246.223 |
| 2 | 131.49 | 63.84 | 7.8 | 87.1 | 2246.826 |
| 3 | 115.43 | 60.84 | 8.0 | 87.5 | 2039.500 |
| 4 | 90.59 | 59.36 | 8.8 | 88.7 | 1764.139 |
| 5 | 79.66 | 58.89 | 9.5 | 89.4 | 1661.567 |
| 6 | 57.36 | 58.92 | 10.0 | 90.0 | 1265.741 |
| 7 | 48.05 | 58.22 | 10.1 | 90.1 | 1069.743 |
| 8 | 29.67 | 57.38 | 10.2 | 90.2 | 669.068 |
| 9 | 27.99 | 56.54 | 10.2 | 90.2 | 631.573 |
The results show that high compression levels do not make a big difference in Space Saving but are extremely expensive in terms of CPU time. For example, compression of a 2.4 MB large serialized object with level 9 takes 69.90 ms with a compressed file size of 212 kB. Level 6 (default value) is 37.23 ms with a compressed file size of 217 kB. Compression with level 2 will take 17.59 ms with a compressed file size of 228 kB. Let's assume that the cache is stored in Redis and we want to take into account the time of transferring an additional amount of information over the network. Transferring of extra 16 kb (228 - 212) through a network with 10 Gbps network bandwidth will take less than 1 ms.
Clone the repository and run from the root:
git clone --recursive --depth=1 https://github.com/pavel-rossinsky/php-zlib-benchmark.git
cd php-zlib-benchmark
php ./src/php_zlib_benchmark.php --file ./samples/sample_2401kb.txt --cycles=100
Adding additional benchmarks on other CPU models and architectures is highly appreciated.
php ./src/php_zlib_benchmark.php --file ./samples/sample_2401kb.txt --cycles=100
Sample length 2401 kB
Compression level 1. Average across 100 tests:
__time_to_deflate_level_1: 16.70 ms
__time_to_inflate_level_1: 6.64 ms
Compressed file size: 292 kB
Space saving: 87.8%
Compression ratio: 8.2
Compression speed: 140.43 MB/s
Decompression speed: 42.97 MB/s
Compression ratio by average time to compress: 492.429
Compression ratio by average time to decompress: 1238.662
--------------
Compression level 2. Average across 100 tests:
__time_to_deflate_level_2: 17.23 ms
__time_to_inflate_level_2: 6.54 ms
Compressed file size: 279 kB
Space saving: 88.3%
Compression ratio: 8.6
Compression speed: 136.12 MB/s
Decompression speed: 41.79 MB/s
Compression ratio by average time to compress: 498.164
Compression ratio by average time to decompress: 1312.447
--------------
Compression level 3. Average across 100 tests:
__time_to_deflate_level_3: 18.70 ms
__time_to_inflate_level_3: 6.67 ms
Compressed file size: 271 kB
Space saving: 88.7%
Compression ratio: 8.8
Compression speed: 125.38 MB/s
Decompression speed: 39.76 MB/s
Compression ratio by average time to compress: 472.968
Compression ratio by average time to decompress: 1326.748
--------------
Compression level 4. Average across 100 tests:
__time_to_deflate_level_4: 24.54 ms
__time_to_inflate_level_4: 6.40 ms
Compressed file size: 244 kB
Space saving: 89.8%
Compression ratio: 9.8
Compression speed: 95.54 MB/s
Decompression speed: 37.34 MB/s
Compression ratio by average time to compress: 399.553
Compression ratio by average time to decompress: 1531.465
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Compression level 5. Average across 100 tests:
__time_to_deflate_level_5: 28.25 ms
__time_to_inflate_level_5: 6.40 ms
Compressed file size: 228 kB
Space saving: 90.5%
Compression ratio: 10.5
Compression speed: 82.99 MB/s
Decompression speed: 34.92 MB/s
Compression ratio by average time to compress: 371.205
Compression ratio by average time to decompress: 1637.958
--------------
Compression level 6. Average across 100 tests:
__time_to_deflate_level_6: 36.73 ms
__time_to_inflate_level_6: 6.30 ms
Compressed file size: 217 kB
Space saving: 90.9%
Compression ratio: 11.0
Compression speed: 63.84 MB/s
Decompression speed: 33.72 MB/s
Compression ratio by average time to compress: 300.725
Compression ratio by average time to decompress: 1754.254
--------------
Compression level 7. Average across 100 tests:
__time_to_deflate_level_7: 42.81 ms
__time_to_inflate_level_7: 6.29 ms
Compressed file size: 215 kB
Space saving: 91.0%
Compression ratio: 11.1
Compression speed: 54.76 MB/s
Decompression speed: 33.50 MB/s
Compression ratio by average time to compress: 260.044
Compression ratio by average time to decompress: 1771.041
--------------
Compression level 8. Average across 100 tests:
__time_to_deflate_level_8: 66.37 ms
__time_to_inflate_level_8: 6.28 ms
Compressed file size: 212 kB
Space saving: 91.1%
Compression ratio: 11.3
Compression speed: 35.33 MB/s
Decompression speed: 33.07 MB/s
Compression ratio by average time to compress: 170.150
Compression ratio by average time to decompress: 1798.682
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Compression level 9. Average across 100 tests:
__time_to_deflate_level_9: 69.89 ms
__time_to_inflate_level_9: 6.31 ms
Compressed file size: 212 kB
Space saving: 91.2%
Compression ratio: 11.3
Compression speed: 33.55 MB/s
Decompression speed: 32.83 MB/s
Compression ratio by average time to compress: 161.914
Compression ratio by average time to decompress: 1793.024
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Level for quickest compression is 1
Level for quickest decompression is 8
Level for most efficient compression (ratio/time) is 2
Level for most efficient decompression (ratio/time) is 8
Compression with level 1 is faster than compression with level 6 by 20.03 ms or 54.5%
Compression with level 1 is faster than compression with level 9 by 53.20 ms or 76.1%
Compression with level 2 is faster than compression with level 6 by 19.50 ms or 53.1%
Compression with level 2 is faster than compression with level 9 by 52.67 ms or 75.4%