Re: Fwd: [JDBC] Re: 9.4-1207 behaves differently with server side prepared statements compared to 9.2-1102

2016-01-13 16:18 GMT+01:00 Albe Laurenz <laurenz(dot)albe(at)wien(dot)gv(dot)at>:

> 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.
>

yes, I though about it too - it is simple, and almost deterministic

Pavel

>
> Yours,
> Laurenz Albe
>