| From: | Albe Laurenz <laurenz(dot)albe(at)wien(dot)gv(dot)at> |
|---|---|
| To: | "'Pavel Stehule *EXTERN*'" <pavel(dot)stehule(at)gmail(dot)com>, Vladimir Sitnikov <sitnikov(dot)vladimir(at)gmail(dot)com> |
| Cc: | Marko Tiikkaja <marko(at)joh(dot)to>, PostgreSQL-development <pgsql-hackers(at)postgresql(dot)org>, Dave Cramer <pg(at)fastcrypt(dot)com> |
| Subject: | Re: Fwd: [JDBC] Re: 9.4-1207 behaves differently with server side prepared statements compared to 9.2-1102 |
| Date: | 2016-01-13 15:18:20 |
| Message-ID: | A737B7A37273E048B164557ADEF4A58B537BDFFD@ntex2010a.host.magwien.gv.at |
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| Lists: | pgsql-hackers pgsql-jdbc |
Pavel Stehule wrote:
> I like a strategy based on risks. Probably there are situation, when the generic plan is great every
> time - INSERTs, UPDATEs via PK, simple SELECTs via PK. generic plan can be well if almost all data has
> similar probability. Elsewhere on bigger data, the probability of pretty slow plan is higher, and then
> we should to prefer custom plan.
>
> so the strategy - if cost of generic plan is less than some MAGIC CONSTANT (can be specified by GUC),
> then use generic plan. Elsewhere use a custom plan everytime.
>
> It allow to controll the plan reusing. When MAGIC CONSTANT = 0 .. use custom plan everytime, When
> MAGIC CONSTANT = M, then use generic plan always.
I have a different idea:
What about a GUC "custom_plan_threshold" that controls after how many
executions a generic plan will be considered, with a default value of 5.
A value of -1 could disable generic plans.
Yours,
Laurenz Albe
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