| From: | Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> |
|---|---|
| To: | Heikki Linnakangas <hlinnakangas(at)vmware(dot)com> |
| Cc: | Claudio Freire <klaussfreire(at)gmail(dot)com>, Jim Nasby <jim(at)nasby(dot)net>, Greg Stark <stark(at)mit(dot)edu>, Mark Kirkwood <mark(dot)kirkwood(at)catalyst(dot)net(dot)nz>, 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: | 2013-12-09 23:52:35 |
| Message-ID: | 30686.1386633155@sss.pgh.pa.us |
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| Lists: | pgsql-hackers |
Heikki Linnakangas <hlinnakangas(at)vmware(dot)com> writes:
> Maybe. Or maybe the heuristic read ahead isn't significant/helpful, when you're prefetching with posix_fadvise anyway.
Yeah. If we're not reading consecutive blocks, readahead is unlikely
to do anything anyhow.
Claudio's comments do suggest that it might be a bad idea to issue a
posix_fadvise when the next block to be examined *is* adjacent to the
current one, though.
regards, tom lane
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