On Thu, 9 Oct 2003, Bruce Momjian wrote:

> scott.marlowe wrote:
> > I was testing to get some idea of how to speed up the speed of pgbench 
> > with IDE drives and the write caching turned off in Linux (i.e. hdparm -W0 
> > /dev/hdx).
> > 
> > The only parameter that seems to make a noticeable difference was setting 
> > wal_sync_method = open_sync.  With it set to either fsync, or fdatasync, 
> > the speed with pgbench -c 5 -t 1000 ran from 11 to 17 tps.  With open_sync 
> > it jumped to the range of 45 to 52 tps.  with write cache on I was getting 
> > 280 to 320 tps.  so, not instead of being 20 to 30 times slower, I'm only 
> > about 5 times slower, much better.
> > 
> > Now I'm off to start a "pgbench -c 10 -t 10000" and pull the power cord 
> > and see if the data gets corrupted with write caching turned on, i.e. do 
> > my hard drives have the ability to write at least some of their cache 
> > during spin down.
> Is this a reason we should switch to open_sync as a default, if it is
> availble, rather than fsync?  I think we are doing a single write before
> fsync a lot more often than we are doing multiple writes before fsync.

Sounds reasonable to me.  Are there many / any scenarios where a plain 
fsync would be faster than open_sync?

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