Hi Sage, Am 26.10.2017 um 13:58 schrieb Sage Weil: > On Thu, 26 Oct 2017, Stefan Priebe - Profihost AG wrote: >> Hi Sage, >> >> Am 25.10.2017 um 21:54 schrieb Sage Weil: >>> 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. i've fixed the zstd compression plugin to use reset stream instead of initializing new objects. What's needed to run only / just the unittest_compression test? Stefan -- To unsubscribe from this list: send the line "unsubscribe ceph-devel" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
