I have heard complaints that /contrib/pg_test_fsync is too slow. I
thought it was impossible to speed up pg_test_fsync without reducing its
accuracy.
However, now that I some consumer-grade SATA 2 drives, I noticed that
the slowness is really in the open_sync test:
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 76.421 ops/sec
2 * 8kB open_sync writes 38.689 ops/sec
4 * 4kB open_sync writes 19.140 ops/sec
8 * 2kB open_sync writes 4.938 ops/sec
16 * 1kB open_sync writes 2.480 ops/sec
These last few lines can take very long, so I developed the attached
patch that scales down the number of tests. This makes it more
reasonable to run pg_test_fsync.
I would like to apply this for PG 9.2.
--
Bruce Momjian <br...@momjian.us> http://momjian.us
EnterpriseDB http://enterprisedb.com
+ It's impossible for everything to be true. +
diff --git a/contrib/pg_test_fsync/pg_test_fsync.c b/contrib/pg_test_fsync/pg_test_fsync.c
new file mode 100644
index 042b02b..970deda
*** a/contrib/pg_test_fsync/pg_test_fsync.c
--- b/contrib/pg_test_fsync/pg_test_fsync.c
*************** test_open_syncs(void)
*** 358,368 ****
printf("(This is designed to compare the cost of writing 16kB\n");
printf("in different write open_sync sizes.)\n");
! test_open_sync("16kB open_sync write", 16);
! test_open_sync(" 8kB open_sync writes", 8);
! test_open_sync(" 4kB open_sync writes", 4);
! test_open_sync(" 2kB open_sync writes", 2);
! test_open_sync(" 1kB open_sync writes", 1);
}
/*
--- 358,368 ----
printf("(This is designed to compare the cost of writing 16kB\n");
printf("in different write open_sync sizes.)\n");
! test_open_sync(" 1 * 16kB open_sync write", 16);
! test_open_sync(" 2 * 8kB open_sync writes", 8);
! test_open_sync(" 4 * 4kB open_sync writes", 4);
! test_open_sync(" 8 * 2kB open_sync writes", 2);
! test_open_sync("16 * 1kB open_sync writes", 1);
}
/*
*************** test_open_sync(const char *msg, int writ
*** 376,381 ****
--- 376,385 ----
ops,
writes;
#endif
+ int save_ops_per_test = ops_per_test;
+
+ /* This test can be long, so scale down the number of tests */
+ ops_per_test = ops_per_test * writes_size / 16;
printf(LABEL_FORMAT, msg);
fflush(stdout);
*************** test_open_sync(const char *msg, int writ
*** 402,407 ****
--- 406,412 ----
#else
printf(NA_FORMAT, "n/a\n");
#endif
+ ops_per_test = save_ops_per_test;
}
static void
--
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