Re: Cached plans and statement generalization

2017-04-26 12:30 GMT+02:00 Konstantin Knizhnik <k(dot)knizhnik(at)postgrespro(dot)ru>:

>
>
> On 26.04.2017 10:49, Konstantin Knizhnik wrote:
>
>
>
> On 26.04.2017 04:00, Tsunakawa, Takayuki wrote: 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.
>
>
> I attach new patch which allows to limit the number of autoprepared
> statements (autoprepare_limit GUC variable).
> Also I did more measurements, now with several concurrent connections and
> read-only statements.
> Results of pgbench with 10 connections, scale 10 and read-only statements
> are below:
>
> Protocol
> TPS
> extended
> 87k
> prepared
> 209k
> simple+autoprepare
> 206k
>
> As you can see, autoprepare provides more than 2 times speed improvement.
>
> Also I tried to measure overhead of parsing (to be able to substitute all
> literals, not only string literals).
> I just added extra call of pg_parse_query. Speed is reduced to 181k.
> So overhead is noticeable, but still making such optimization useful.
> This is why I want to ask question: is it better to implement slower but
> safer and more universal solution?
>

Unsafe solution has not any sense, and it is dangerous (80% of database
users has not necessary knowledge). If somebody needs the max possible
performance, then he use explicit prepared statements.

Regards

Pavel

>
>
> --
> Konstantin Knizhnik
> Postgres Professional: http://www.postgrespro.com
> The Russian Postgres Company
>
>
>
> --
> Sent via pgsql-hackers mailing list (pgsql-hackers(at)postgresql(dot)org)
> To make changes to your subscription:
> http://www.postgresql.org/mailpref/pgsql-hackers
>
>