Am 12.11.2017 um 17:55 schrieb Sage Weil: > On Wed, 25 Oct 2017, Sage Weil wrote: >> On Wed, 25 Oct 2017, Stefan Priebe - Profihost AG wrote: >>> Hello, >>> >>> in the lumious release notes is stated that zstd is not supported by >>> bluestor due to performance reason. I'm wondering why btrfs instead >>> states that zstd is as fast as lz4 but compresses as good as zlib. >>> >>> Why is zlib than supported by bluestor? And why does btrfs / facebook >>> behave different? >>> >>> "BlueStore supports inline compression using zlib, snappy, or LZ4. (Ceph >>> also supports zstd for RGW compression but zstd is not recommended for >>> BlueStore for performance reasons.)" >> >> zstd will work but in our testing the performance wasn't great for >> bluestore in particular. The problem was that for each compression run >> there is a relatively high start-up cost initializing the zstd >> context/state (IIRC a memset of a huge memory buffer) that dominated the >> execution time... primarily because bluestore is generally compressing >> pretty small chunks of data at a time, not big buffers or streams. >> >> Take a look at unittest_compression timings on compressing 16KB buffers >> (smaller than bluestore needs usually, but illustrated of the problem): >> >> [ RUN ] Compressor/CompressorTest.compress_16384/0 >> [plugin zlib (zlib/isal)] >> [ OK ] Compressor/CompressorTest.compress_16384/0 (294 ms) >> [ RUN ] Compressor/CompressorTest.compress_16384/1 >> [plugin zlib (zlib/noisal)] >> [ OK ] Compressor/CompressorTest.compress_16384/1 (1755 ms) >> [ RUN ] Compressor/CompressorTest.compress_16384/2 >> [plugin snappy (snappy)] >> [ OK ] Compressor/CompressorTest.compress_16384/2 (169 ms) >> [ RUN ] Compressor/CompressorTest.compress_16384/3 >> [plugin zstd (zstd)] >> [ OK ] Compressor/CompressorTest.compress_16384/3 (4528 ms) >> >> It's an order of magnitude slower than zlib or snappy, which probably >> isn't acceptable--even if it is a bit smaller. > > Update! Zstd developer Yann Collet debugged this and it turns out it was > a build issue, fixed by https://github.com/ceph/ceph/pull/18879/files > (missing quotes! yeesh). The results now look quite good! > > [ RUN ] Compressor/CompressorTest.compress_16384/0 > [plugin zlib (zlib/isal)] > [ OK ] Compressor/CompressorTest.compress_16384/0 (370 ms) > [ RUN ] Compressor/CompressorTest.compress_16384/1 > [plugin zlib (zlib/noisal)] > [ OK ] Compressor/CompressorTest.compress_16384/1 (1926 ms) > [ RUN ] Compressor/CompressorTest.compress_16384/2 > [plugin snappy (snappy)] > [ OK ] Compressor/CompressorTest.compress_16384/2 (163 ms) > [ RUN ] Compressor/CompressorTest.compress_16384/3 > [plugin zstd (zstd)] > [ OK ] Compressor/CompressorTest.compress_16384/3 (723 ms) > > Not as fast as snappy, but somewhere between intel-accellerated zlib and > non-accellerated zlib, with better compression ratios. > > Also, the zstd compression level is currently hard-coded to level 5. > That should be fixed at some point. > > We can backport this to luminous so it's available in 12.2.3. thanks a lot - i already ported your improvements and the fix to my local branch but will also change the compression level to 3 or may be 2. 5 is still far too slow and also higher than most apps using zstd. I'm happy that my post to the zstd github project had so much success. Greets, Stefan _______________________________________________ ceph-users mailing list ceph-users@xxxxxxxxxxxxxx http://lists.ceph.com/listinfo.cgi/ceph-users-ceph.com
 |