b5c99cc908
Summary: FILE_FLAG_WRITE_THROUGH is for disabling device on-board cache in windows API, which should be disabled if user doesn't need system cache. There was a perf issue related with this, we found during memtable flush, the high percentile latency jumps significantly. During profiling, we found those high latency (P99.9) read requests got queue-jumped by write requests from memtable flush and takes 80ms or even more time to wait, even when SSD overall IO throughput is relatively low. After enabling FILE_FLAG_WRITE_THROUGH, we rerun the test found high percentile latency drops a lot without observable impact on writes. Scenario 1: 40MB/s + 40MB/s R/W compaction throughput Original | FILE_FLAG_WRITE_THROUGH | Percentage reduction --------------------------------------------------------------- P99.9 | 56.897 ms | 35.593 ms | -37.4% P99 | 3.905 ms | 3.896 ms | -2.8% Scenario 2: 14MB/s + 14MB/s R/W compaction throughput, cohosted with 100+ other rocksdb instances have manually triggered memtable flush operations (memtable is tiny), creating a lot of randomized the small file writes operations during test. Original | FILE_FLAG_WRITE_THROUGH | Percentage reduction --------------------------------------------------------------- P99.9 | 86.227 ms | 50.436 ms | -41.5% P99 | 8.415 ms | 3.356 ms | -60.1% Closes https://github.com/facebook/rocksdb/pull/3225 Differential Revision: D6624174 Pulled By: miasantreble fbshipit-source-id: 321b86aee9d74470840c70e5d0d4fa9880660a91
This directory contains interfaces and implementations that isolate the rest of the package from platform details. Code in the rest of the package includes "port.h" from this directory. "port.h" in turn includes a platform specific "port_<platform>.h" file that provides the platform specific implementation. See port_posix.h for an example of what must be provided in a platform specific header file.