On Fri, 2005-06-24 at 10:19 -0500, Jim C. Nasby wrote: > On Fri, Jun 24, 2005 at 09:37:23AM -0400, Tom Lane wrote: > > ITAGAKI Takahiro <[EMAIL PROTECTED]> writes: > > > ... So I'll post the new results: > > > > > checkpoint_ | writeback | > > > segments | cache | open_sync | fsync=false | O_DIRECT only | > > > fsync_direct | open_direct > > > ------------+-----------+-----------+---------------+---------------+---------------+-------------- > > > [3] 3 | off | 38.2 tps | 138.8(+263.5%)| 38.6(+ 1.2%) | > > > 38.5(+ 0.9%) | 38.5(+ 0.9%) > > > > Yeah, this is about what I was afraid of: if you're actually fsyncing > > then you get at best one commit per disk revolution, and the negotiation > > with the OS is down in the noise. > > > > At this point I'm inclined to reject the patch on the grounds that it > > adds complexity and portability issues, without actually buying any > > useful performance improvement. The write-cache-on numbers are not > > going to be interesting to any serious user :-( > > Is there anyone with a battery-backed RAID controller that could run > these tests? I suspect that in that case the differences might be closer > to 1 or 2 rather than 3, which would make the patch much more valuable.
I applied the O_DIRECT patch to 8.0.3 and I tested this on a battery-backed RAID controller with 128MB of cache and 5 7200RPM SATA disks. All caches are write-back. The xlog and data are on the same JFS volume. pgbench was run with a scale factor of 1000 and 100000 total transactions. Clients varied from 10 to 100. Clients | fsync | open_direct ------------------------------------ 10 | 81 | 98 (+21%) 100 | 100 | 105 ( +5%) ------------------------------------ No problems were experienced. The patch seems to give a useful boost! -jwb ---------------------------(end of broadcast)--------------------------- TIP 5: don't forget to increase your free space map settings
