Thread: test_fsync open_sync test
Is there a value to this test_fsync test? Compare open_sync with different sizes:(This is designed to compare the cost of one largesync'ed write and two smaller sync'edwrites.) open_sync 16k write 242.563 ops/sec 2 open_sync 8k writes 752.752ops/sec It compares the cost of doing larger vs. two smaller open_sync writes. -- Bruce Momjian <bruce@momjian.us> http://momjian.us EnterpriseDB http://enterprisedb.com + It's impossible for everything to be true. +
Bruce Momjian wrote: > Is there a value to this test_fsync test? > > Compare open_sync with different sizes: > (This is designed to compare the cost of one large > sync'ed write and two smaller sync'ed writes.) > open_sync 16k write 242.563 ops/sec > 2 open_sync 8k writes 752.752 ops/sec > > It compares the cost of doing larger vs. two smaller open_sync writes. > Might be some value for determining things like what the optimal WAL block size to use is. All these tests are kind of hard to use effectively still, I'm not sure if it's time to start trimming tests yet until we've made more progress on interpreting results first. -- Greg Smith 2ndQuadrant US greg@2ndQuadrant.com Baltimore, MD PostgreSQL Training, Services, and 24x7 Support www.2ndQuadrant.us "PostgreSQL 9.0 High Performance": http://www.2ndQuadrant.com/books
Greg Smith wrote: > Bruce Momjian wrote: > > Is there a value to this test_fsync test? > > > > Compare open_sync with different sizes: > > (This is designed to compare the cost of one large > > sync'ed write and two smaller sync'ed writes.) > > open_sync 16k write 242.563 ops/sec > > 2 open_sync 8k writes 752.752 ops/sec > > > > It compares the cost of doing larger vs. two smaller open_sync writes. > > > > Might be some value for determining things like what the optimal WAL > block size to use is. All these tests are kind of hard to use > effectively still, I'm not sure if it's time to start trimming tests yet > until we've made more progress on interpreting results first. OK, thanks for the feedback. I just wanted to make sure it wasn't a stupid test. -- Bruce Momjian <bruce@momjian.us> http://momjian.us EnterpriseDB http://enterprisedb.com + It's impossible for everything to be true. +
Greg Smith wrote: > Bruce Momjian wrote: > > Is there a value to this test_fsync test? > > > > Compare open_sync with different sizes: > > (This is designed to compare the cost of one large > > sync'ed write and two smaller sync'ed writes.) > > open_sync 16k write 242.563 ops/sec > > 2 open_sync 8k writes 752.752 ops/sec > > > > It compares the cost of doing larger vs. two smaller open_sync writes. > > > > Might be some value for determining things like what the optimal WAL > block size to use is. All these tests are kind of hard to use > effectively still, I'm not sure if it's time to start trimming tests yet > until we've made more progress on interpreting results first. FYI, I beefed up the testing for this in test_fsync: Compare open_sync with different write sizes:(This is designed to compare the cost of writing 16kin different write open_syncsizes.) 1 16k open_sync write 723.824 ops/sec 2 8k open_sync writes 347.979ops/sec 4 4k open_sync writes 215.114 ops/sec 8 2k open_sync writes 174.613ops/sec 16 1k open_sync writes 87.496 ops/sec -- Bruce Momjian <bruce@momjian.us> http://momjian.us EnterpriseDB http://enterprisedb.com + It's impossible for everything to be true. +