| From: | Claudio Freire <klaussfreire(at)gmail(dot)com> |
|---|---|
| To: | Mark Kirkwood <mark(dot)kirkwood(at)catalyst(dot)net(dot)nz> |
| Cc: | Heikki Linnakangas <hlinnakangas(at)vmware(dot)com>, Jim Nasby <jim(at)nasby(dot)net>, Greg Stark <stark(at)mit(dot)edu>, Josh Berkus <josh(at)agliodbs(dot)com>, Robert Haas <robertmhaas(at)gmail(dot)com>, PostgreSQL-development <pgsql-hackers(at)postgresql(dot)org> |
| Subject: | Re: ANALYZE sampling is too good |
| Date: | 2013-12-10 04:18:06 |
| Message-ID: | CAGTBQpYRz7z_Lhf3T9BrQKJ12sZA9fJL78D7gDfPTvKCjELUUQ@mail.gmail.com |
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On Tue, Dec 10, 2013 at 12:13 AM, Mark Kirkwood
<mark(dot)kirkwood(at)catalyst(dot)net(dot)nz> wrote:
> Just one more...
>
> The Intel 520 with ext4:
>
>
> Without patch: ANALYZE pgbench_accounts 5s
> With patch: ANALYZE pgbench_accounts 1s
>
> And double checking -
> With patch, but effective_io_concurrency = 1: ANALYZE pgbench_accounts 5s
>
> These results look more like Heikki's. Which suggests more benefit on SSD
> than spinning disks. Some more data points (apart from mine) would be good
> to see tho.
Assuming ANALYZE is sampling less than 5% of the table, I'd say
fadvising will always be a win.
I'd also suggest higher e_i_c for rotating media. Rotating media has
longer latencias, and e_i_c has to be computed in terms of latency,
rather than "spindles" when doing prefetch.
For backward index scans, I found the optimum number for a single
spindle to be about 20.
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