Re: Cached plans and statement generalization

On 26.04.2017 04:00, Tsunakawa, Takayuki wrote:
> From: pgsql-hackers-owner(at)postgresql(dot)org
>> [mailto:pgsql-hackers-owner(at)postgresql(dot)org] On Behalf Of Konstantin
>> Knizhnik
>> Well, first of all I want to share results I already get: pgbench with default
>> parameters, scale 10 and one connection:
>>
>> So autoprepare is as efficient as explicit prepare and can increase
>> performance almost two times.
> This sounds great.
>
> BTW, when are the autoprepared statements destroyed?
Right now them are destroyed only in case of receiving invalidation
message (when catalog is changed).
Prepared statements are local to backend and are located in backend's
memory.
It is unlikely, that there will be too much different queries which
cause memory overflow.
But in theory such situation is certainly possible.

> Are you considering some upper limit on the number of prepared statements?
In this case we need some kind of LRU for maintaining cache of
autoprepared statements.
I think that it is good idea to have such limited cached - it can avoid
memory overflow problem.
I will try to implement it.

> Regards
> Takayuki Tsunakawa
>
>

--
Konstantin Knizhnik
Postgres Professional: http://www.postgrespro.com
The Russian Postgres Company