Re: [GENERAL] pg_test_fsync performance

От: Andy Colson
Тема: Re: [GENERAL] pg_test_fsync performance
Дата: ,
Msg-id: ed88c619-da94-5e97-f267-9a1ff26ef05b@squeakycode.net
(см: обсуждение, исходный текст)
Ответ на: [GENERAL] pg_test_fsync performance  (Karri Niemelä)
Список: pgsql-general

On 04/25/2017 05:40 AM, Karri Niemelä wrote:
> Hi. Wondering what sort of results are people seeing on modern servers when running pg_test_fsync?
>
> Thanks,
> Karri

4 sata HD, hardware raid 10
4 core Xeon E5504
Box is Busy


5 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                     15984.370 ops/sec      63 usecs/op
         fdatasync                         16100.336 ops/sec      62 usecs/op
         fsync                             15109.988 ops/sec      66 usecs/op
         fsync_writethrough                            n/a
         open_sync                         16849.201 ops/sec      59 usecs/op

Compare file sync methods using two 8kB writes:
(in wal_sync_method preference order, except fdatasync is Linux's default)
         open_datasync                      8638.443 ops/sec     116 usecs/op
         fdatasync                         12036.359 ops/sec      83 usecs/op
         fsync                             11807.447 ops/sec      85 usecs/op
         fsync_writethrough                            n/a
         open_sync                          8532.569 ops/sec     117 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         14205.165 ops/sec      70 usecs/op
          2 *  8kB open_sync writes         8506.969 ops/sec     118 usecs/op
          4 *  4kB open_sync writes         4979.092 ops/sec     201 usecs/op
          8 *  2kB open_sync writes         2658.138 ops/sec     376 usecs/op
         16 *  1kB open_sync writes         1343.359 ops/sec     744 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               13331.347 ops/sec      75 usecs/op
         write, close, fsync               13435.198 ops/sec      74 usecs/op

Non-sync'ed 8kB writes:
         write                            297771.626 ops/sec       3 usecs/op




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