| From: | Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> |
|---|---|
| To: | Andres Freund <andres(at)anarazel(dot)de> |
| Cc: | Simon Riggs <simon(at)2ndquadrant(dot)com>, Robert Haas <robertmhaas(at)gmail(dot)com>, Alvaro Herrera <alvherre(at)2ndquadrant(dot)com>, Michael Paquier <michael(dot)paquier(at)gmail(dot)com>, Amit Kapila <amit(dot)kapila16(at)gmail(dot)com>, PostgreSQL-development <pgsql-hackers(at)postgresql(dot)org> |
| Subject: | Re: Turning off HOT/Cleanup sometimes |
| Date: | 2014-09-19 20:35:19 |
| Message-ID: | 21789.1411158919@sss.pgh.pa.us |
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| Lists: | pgsql-hackers |
Andres Freund <andres(at)anarazel(dot)de> writes:
> On September 19, 2014 10:16:35 PM CEST, Simon Riggs <simon(at)2ndquadrant(dot)com> wrote:
>> Are you saying this is a problem or a benefit? (and please explain
>> why).
> I have no idea what Robert is thinking of, but I'd imagine its horrible for workloads with catalog bloat. Like ones involving temp tables.
Yeah. But it's also the case that we know a good deal more about the
access patterns for system-driven catalog updates than we do about user
queries. ISTM we could probably suppress HOT pruning during catalog
*scans* and instead try to do it when a system-driven heap_update
occurs.
Having said that, this could reasonably be considered outside the scope
of a patch that's trying to improve the behavior for user queries.
But if the patch author doesn't want to expand the scope like that,
ISTM he ought to ensure that the behavior *doesn't* change for system
accesses, rather than trying to convince us that disabling HOT for
system updates is a good idea.
regards, tom lane
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