pg_test_fsync使用记录

pg_test_fsync

pg_test_fsync旨在让您合理地了解特定系统上最快的wal_sync_method，以及在发生识别的I / O问题时提供诊断信息。 但是，pg_test_fsync所显示的差异在实际数据库吞吐量方面可能没有任何显着差异，特别是因为许多数据库服务器不受其事务日志的限制。 pg_test_fsync报告每个wal_sync_method的平均文件同步操作时间（以微秒为单位），也可用于通知努力优化commit_delay的值。

使用非常简单，只需要设置一下－s参数，每个测试执行多少时间，也可以使用默认的5s。

root@XXX# ./pg_test_fsync -s 10
10 seconds per test
O_DIRECT supported on this platform for open_datasync and open_sync.

Compare file sync methods using one 8kB write:
(in wal_sync_method preference order, except fdatasync is Linux's default)
        open_datasync                       434.638 ops/sec    2301 usecs/op
        fdatasync                           428.840 ops/sec    2332 usecs/op
        fsync                               434.291 ops/sec    2303 usecs/op
        fsync_writethrough                            n/a
        open_sync                           441.457 ops/sec    2265 usecs/op

Compare file sync methods using two 8kB writes:
(in wal_sync_method preference order, except fdatasync is Linux's default)
        open_datasync                       227.454 ops/sec    4396 usecs/op
        fdatasync                           422.669 ops/sec    2366 usecs/op
        fsync                               433.111 ops/sec    2309 usecs/op
        fsync_writethrough                            n/a
        open_sync                           215.747 ops/sec    4635 usecs/op

Compare open_sync with different write sizes:
(This is designed to compare the cost of writing 16kB in different write
open_sync sizes.)
         1 * 16kB open_sync write           418.466 ops/sec    2390 usecs/op
         2 *  8kB open_sync writes          219.613 ops/sec    4553 usecs/op
         4 *  4kB open_sync writes          109.423 ops/sec    9139 usecs/op
         8 *  2kB open_sync writes           54.230 ops/sec   18440 usecs/op
        16 *  1kB open_sync writes           28.370 ops/sec   35249 usecs/op

Test if fsync on non-write file descriptor is honored:
(If the times are similar, fsync() can sync data written on a different
descriptor.)
        write, fsync, close                 424.550 ops/sec    2355 usecs/op
        write, close, fsync                 427.676 ops/sec    2338 usecs/op

Non-sync'ed 8kB writes:
        write                            147612.547 ops/sec       7 usecs/op

具体每项测试都有指出测试条件。