On Wed, Jul 28, 2010 at 9:18 AM, Yeb Havinga
<yebhavinga@gmail.com> wrote:
Yeb Havinga wrote:
Due to the LBA remapping of the SSD, I'm not sure of putting files that are sequentially written in a different partition (together with e.g. tables) would make a difference: in the end the SSD will have a set new blocks in it's buffer and somehow arrange them into sets of 128KB of 256KB writes for the flash chips. See also http://www.anandtech.com/show/2899/2
But I ran out of ideas to test, so I'm going to test it anyway.
pgbench -c 10 -M prepared -T 3600 -l test
starting vacuum...end.
transaction type: TPC-B (sort of)
scaling factor: 300
query mode: prepared
number of clients: 10
duration: 3600 s
number of transactions actually processed: 10856359
tps = 3015.560252 (including connections establishing)
tps = 3015.575739 (excluding connections establishing)
This is about 25% faster than data and xlog combined on the same filesystem.
The trick may be in kjournald for which there is 1 for each ext3 journalled file system. I learned back in Red Hat 4 pre U4 kernels there was a problem with kjournald that would either cause 30 second hangs or lock up my server completely when pg_xlog and data were on the same file system plus a few other "right" things going on.
Given the multicore world we have today, I think it makes sense that multiple ext3 file systems, and the kjournald's that service them, is faster than a single combined file system.
Greg