Re: FreeBSD page size

Just curious, but Bruce(?) mentioned that apparently a 32k block size was
found to show a 15% improvement ... care to run one more test? :)

On Wed, 3 Sep 2003, Vivek Khera wrote:

> Ok... simple tests have completed.  Here are some numbers.
>
> FreeBSD 4.8
> PG 7.4b2
> 4GB Ram
> Dual Xeon 2.4GHz processors
> 14 U320 SCSI disks attached to Dell PERC3/DC RAID controller in RAID 5
>  config with 32k stripe size
>
> Dump file:
> -rw-r--r--  1 vivek  wheel  1646633745 Aug 28 11:01 19-Aug-2003.dump
>
> When restored (after deleting one index that took up ~1Gb -- turned
> out it was redundant to another multi-column index):
>
> % df -k /u/d02
> Filesystem    1K-blocks     Used     Avail Capacity  Mounted on
> /dev/amrd1s1e 226408360 18067260 190228432     9%    /u/d02
>
>
>
> postgresql.conf alterations from standard:
> shared_buffers = 60000
> sort_mem = 8192
> vacuum_mem=131702
> max_fsm_pages=1000000
> effective_cache_size=25600
> random_page-cost = 2
>
>
> restore time: 14777 seconds
> vacuum analyze time: 30 minutes
> select count(*) from user_list where owner_id=315;   50388.64 ms
>
>
> the restore complained often about checkpoints occurring every few
> seconds:
>
> Sep  2 11:57:14 d02 postgres[49721]: [5-1] LOG:  checkpoints are occurring too frequently (15 seconds apart)
> Sep  2 11:57:14 d02 postgres[49721]: [5-2] HINT:  Consider increasing CHECKPOINT_SEGMENTS.
>
> The HINT threw me off since I had to set checkpoint_segments in
> postgresql.conf, where as CHECKPOINT_SEGMENTS implied to me a
> compile-time constant.
>
> Anyhow, so I deleted the PG data directory, and made these two
> changes:
>
> checkpoint_segments=50
> sort_mem = 131702
>
> This *really* improved the time for the restore:
>
> restore time: 11594 seconds
>
> then I reset the checkpoint_segments and sort_mem back to old
> values...
>
> vacuum analyze time is still 30 minutes
> select count(*) from user_list where owner_id=315;   51363.98 ms
>
> so the select appears a bit slower but it is hard to say why.  the
> system is otherwise idle as it is not in production yet.
>
>
> Then I took the suggestion to update PG's page size to 16k and did the
> same increase on sort_mem and checkpoint_segments as above.  I also
> halved the shared_buffers and max_fsm_pages  (probably should have
> halved the effective_cache_size too...)
>
> restore time: 11322 seconds
> vacuum analyze time: 27 minutes
> select count(*) from user_list where owner_id=315;   48267.66 ms
>
>
> Granted, given this simple test it is hard to say whether the 16k
> blocks will make an improvement under live load, but I'm gonna give it
> a shot.  The 16k block size shows me roughly 2-6% improvement on these
> tests.
>
> So throw in my vote for 16k blocks on FreeBSD (and annotate the docs
> to tell which parameters need to be halved to account for it).
>
>
> --
> =-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=
> Vivek Khera, Ph.D.                Khera Communications, Inc.
> Internet: khera@kciLink.com       Rockville, MD       +1-240-453-8497
> AIM: vivekkhera Y!: vivek_khera   http://www.khera.org/~vivek/
>
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