| From: | Andres Freund <andres(at)anarazel(dot)de> |
|---|---|
| To: | Robert Haas <robertmhaas(at)gmail(dot)com> |
| Cc: | Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>, Michael Paquier <michael(dot)paquier(at)gmail(dot)com>, Kyotaro HORIGUCHI <horiguchi(dot)kyotaro(at)lab(dot)ntt(dot)co(dot)jp>, David Steele <david(at)pgmasters(dot)net>, Jim Nasby <Jim(dot)Nasby(at)bluetreble(dot)com>, Craig Ringer <craig(at)2ndquadrant(dot)com>, PostgreSQL mailing lists <pgsql-hackers(at)postgresql(dot)org> |
| Subject: | Re: Protect syscache from bloating with negative cache entries |
| Date: | 2017-12-01 21:31:13 |
| Message-ID: | 20171201213113.z4gbol66ipvg5b4o@alap3.anarazel.de |
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| Lists: | pgsql-hackers |
On 2017-12-01 16:20:44 -0500, Robert Haas wrote:
> Well, yeah, that would be insane. But I think even something very
> rough could work well enough. I think our goal should be to eliminate
> cache entries that are have gone unused for many *minutes*, and
> there's no urgency about getting it to any sort of exact value. For
> non-idle backends, using the most recent statement start time as a
> proxy would probably be plenty good enough. Idle backends might need
> a bit more thought.
Our timer framework is flexible enough that we can install a
once-a-minute timer without much overhead. That timer could increment a
'cache generation' integer. Upon cache access we write the current
generation into relcache / syscache (and potentially also plancache?)
entries. Not entirely free, but cheap enough. In those once-a-minute
passes entries that haven't been touched in X cycles get pruned.
Greetings,
Andres Freund
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