| From: | Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> |
|---|---|
| To: | Robert Haas <robertmhaas(at)gmail(dot)com> |
| Cc: | Bruce Momjian <bruce(at)momjian(dot)us>, Kyotaro HORIGUCHI <horiguchi(dot)kyotaro(at)lab(dot)ntt(dot)co(dot)jp>, "Ideriha, Takeshi" <ideriha(dot)takeshi(at)jp(dot)fujitsu(dot)com>, "pgsql-hackers(at)lists(dot)postgresql(dot)org" <pgsql-hackers(at)lists(dot)postgresql(dot)org>, "Tsunakawa, Takayuki" <tsunakawa(dot)takay(at)jp(dot)fujitsu(dot)com>, "alvherre(at)alvh(dot)no-ip(dot)org" <alvherre(at)alvh(dot)no-ip(dot)org>, "andres(at)anarazel(dot)de" <andres(at)anarazel(dot)de>, "michael(dot)paquier(at)gmail(dot)com" <michael(dot)paquier(at)gmail(dot)com>, "david(at)pgmasters(dot)net" <david(at)pgmasters(dot)net>, "craig(at)2ndquadrant(dot)com" <craig(at)2ndquadrant(dot)com> |
| Subject: | Re: Protect syscache from bloating with negative cache entries |
| Date: | 2019-01-18 20:57:17 |
| Message-ID: | 1391.1547845037@sss.pgh.pa.us |
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| Lists: | pgsql-hackers |
Robert Haas <robertmhaas(at)gmail(dot)com> writes:
> On Thu, Jan 17, 2019 at 2:48 PM Bruce Momjian <bruce(at)momjian(dot)us> wrote:
>> Unfortunately, because we have not found something we are happy with, we
>> have done nothing. I agree LRU can be expensive. What if we do some
>> kind of clock sweep and expiration like we do for shared buffers? I
>> think the trick is figuring how frequently to do the sweep. What if we
>> mark entries as unused every 10 queries, mark them as used on first use,
>> and delete cache entries that have not be used in the past 10 queries.
> I still think wall-clock time is a perfectly reasonable heuristic.
The easy implementations of that involve putting gettimeofday() calls
into hot code paths, which would be a Bad Thing. But maybe we could
do this only at transaction or statement start, and piggyback on the
gettimeofday() calls that already happen at those times.
regards, tom lane
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