Thread: test_fsync open_sync test

test_fsync open_sync test

From
Bruce Momjian
Date:
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. +


Re: test_fsync open_sync test

From
Greg Smith
Date:
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
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Re: test_fsync open_sync test

From
Bruce Momjian
Date:
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. +


Re: test_fsync open_sync test

From
Bruce Momjian
Date:
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. +