| From: | Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> |
|---|---|
| To: | Robert Haas <robertmhaas(at)gmail(dot)com> |
| Cc: | 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 04:17:09 |
| Message-ID: | 85587.1512101829@sss.pgh.pa.us |
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| Lists: | pgsql-hackers |
Robert Haas <robertmhaas(at)gmail(dot)com> writes:
> On Wed, Nov 29, 2017 at 11:17 PM, Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> wrote:
>> The thing that makes me uncomfortable about this is that we used to have a
>> catcache size limitation mechanism, and ripped it out because it had too
>> much overhead (see commit 8b9bc234a). I'm not sure how we can avoid that
>> problem within a fresh implementation.
> At the risk of beating a dead horse, I still think that the amount of
> wall clock time that has elapsed since an entry was last accessed is
> very relevant.
While I don't object to that statement, I'm not sure how it helps us
here. If we couldn't afford DLMoveToFront(), doing a gettimeofday()
during each syscache access is surely right out.
regards, tom lane
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