RE: Protect syscache from bloating with negative cache entries

Hi Horiguchi-san, Bruce,

From: Bruce Momjian [mailto:bruce@momjian.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
forthe DBA to be able to control the cache memory amount.  Otherwise, if many concurrent connections access many
partitionswithin a not-so-long duration, then the cache eviction can't catch up and ends up in OOM.  How about the
followingquestions 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