| From: | "Tsunakawa, Takayuki" <tsunakawa(dot)takay(at)jp(dot)fujitsu(dot)com> |
|---|---|
| To: | Kyotaro HORIGUCHI <horiguchi(dot)kyotaro(at)lab(dot)ntt(dot)co(dot)jp>, 'Bruce Momjian' <bruce(at)momjian(dot)us> |
| Cc: | "GavinFlower(at)archidevsys(dot)co(dot)nz" <GavinFlower(at)archidevsys(dot)co(dot)nz>, "robertmhaas(at)gmail(dot)com" <robertmhaas(at)gmail(dot)com>, "tgl(at)sss(dot)pgh(dot)pa(dot)us" <tgl(at)sss(dot)pgh(dot)pa(dot)us>, "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>, "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>, "Jim(dot)Nasby(at)bluetreble(dot)com" <Jim(dot)Nasby(at)bluetreble(dot)com>, "craig(at)2ndquadrant(dot)com" <craig(at)2ndquadrant(dot)com> |
| Subject: | RE: Protect syscache from bloating with negative cache entries |
| Date: | 2019-01-25 08:14:19 |
| Message-ID: | 0A3221C70F24FB45833433255569204D1FB70EFB@G01JPEXMBYT05 |
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| Lists: | pgsql-hackers |
Hi Horiguchi-san, Bruce,
From: Bruce Momjian [mailto:bruce(at)momjian(dot)us]
> I suggest you go with just syscache_prune_min_age, get that into PG 12,
> and we can then reevaluate what we need. If you want to hard-code a
> minimum cache size where no pruning will happen, maybe based on the system
> catalogs or typical load, that is fine.
Please forgive me if I say something silly (I might have got lost.)
Are you suggesting to make the cache size limit system-defined and uncontrollable by the user? I think it's necessary for the DBA to be able to control the cache memory amount. Otherwise, if many concurrent connections access many partitions within a not-so-long duration, then the cache eviction can't catch up and ends up in OOM. How about the following questions I asked in my previous mail?
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This is a pure question. How can we answer these questions from users?
* What value can I set to cache_memory_target when I can use 10 GB for the caches and max_connections = 100?
* How much RAM do I need to have for the caches when I set cache_memory_target = 1M?
The user tends to estimate memory to avoid OOM.
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Regards
Takayuki Tsunakawa
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