Re: [HACKERS] Cached plans and statement generalization

On 31.07.2018 12:12, Yamaji, Ryo wrote:
>
> 3. I confirmed the transition of the amount of the memory when it tried to prepare query
> of the number that exceeded the value specified for autoprepare_limit.
> [autoprepare_limit=1 and execute 10 different queries]
>     plan cache context: 1032 used
>     plan cache context: 39832 used
>     plan cache context: 78552 used
>     plan cache context: 117272 used
>     plan cache context: 155952 used
>     plan cache context: 194632 used
>     plan cache context: 233312 used
>     plan cache context: 272032 used
>     plan cache context: 310712 used
>     plan cache context: 349392 used
>     plan cache context: 388072 used
>
> I feel the doubt in an increase of the memory utilization when I execute a lot of
> query though cached query is one (autoprepare_limit=1).
> This behavior is correct?

I failed to reproduce the problem.
I used the following non-default configuration parameters:

autoprepare_limit=1
autoprepare_threshold=1

create dummy database:

create table foo(x integer primary key, y integer);
insert into foo values (generate_series(1,10000), 0);

and run different queries,  like:

postgres=# select *  from foo where x=1;
postgres=# select *  from foo where x+x=1;
postgres=# select *  from foo where x+x+x=1;
postgres=# select *  from foo where x+x+x+x=1;
...

and check size of CacheMemoryContext using gdb - it is not increased.

Can you please send me your test?