On 06/12/13 05:13, Skarsol wrote:
On Thu, Dec 5, 2013 at 9:50 AM, Scott Marlowe <scott.marlowe@xxxxxxxxx>wrote:
On Thu, Dec 5, 2013 at 8:16 AM, Skarsol <skarsol@xxxxxxxxx> wrote:
psql (PostgreSQL) 9.2.5
Red Hat Enterprise Linux Server release 6.4 (Santiago)
Linux 2.6.32-358.6.1.el6.x86_64 #1 SMP Fri Mar 29 16:51:51 EDT 2013
x86_64
x86_64 x86_64 GNU/Linux
All relevant filesystems are ext4
Changes from defaults:
max_connections = 500
shared_buffers = 32000MB
temp_buffers = 24MB
work_mem = 1GB
maintenance_work_mem = 5GB
wal_level = archive
wal_buffers = 16MB
checkpoint_completion_target = 0.9
archive_mode = on
archive_command = 'test ! -f /databases/pg_archive/db/%f && cp %p
/databases/pg_archive/db/%f'
effective_cache_size = 64000MB
default_statistics_target = 5000
log_checkpoints = on
stats_temp_directory = '/tmp/pgstat'
OK I'd make the following changes.
1: Drop shared_buffers to something like 1000MB
2: drop work_mem to 16MB or so. 1GB is pathological, as it can make
the machine run out of memory quite fast.
3: drop max_connections to 100 or so. if you really need 500 conns,
then work_mem of 1G is that much worse.
Next, move pg_xlog OFF the SSDs and back onto spinning media and put
your data/base dir on the SSDs.
SSDs aren't much faster, if at all, for pg_xlog, but are much much
faster for data/base files.
Also changing the io schduler for the SSDs to noop:
http://git.kernel.org/cgit/linux/kernel/git/torvalds/linux.git/tree/Documentation/block/switching-sched.txt?id=HEAD
Changing the scheduler to noop seems to have had a decent effect. I've made
the other recommended changes other than the connections as we do need that
many currently. We're looking to implement pg_bouncer which should help
with that.
What model SSD are you using? Some can work better with deadline than
noop (as their own scheduling firmware may be pretty poor). Also, check
if there are updates for the SSD firmware. I have a couple of Crucial
M4s that changed from being fairly average to very fast indeed after
getting later firmware...
Cheers
Mark
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