Re: PoC plpgsql - possibility to force custom or generic plan

2017-04-06 8:08 GMT+02:00 Pavel Stehule <pavel(dot)stehule(at)gmail(dot)com>:

>
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> 2017-04-05 23:22 GMT+02:00 Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>:
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>> Andres Freund <andres(at)anarazel(dot)de> writes:
>> > I'd like some input from other committers whether we want this. I'm
>> > somewhat doubtful, but don't have particularly strong feelings.
>>
>> I don't really want to expose the workings of the plancache at user level.
>> The heuristics it uses certainly need work, but it'll get hard to change
>> those once there are SQL features depending on it.
>>
>
> I am very sceptical about enhancing heuristics - but I am open to any
> proposals.
>
> The advanced users disable a plan cache with dynamic SQL. But this
> workaround has strong disadvantages:
>
> 1. it is vulnerable to SQL injection
> 2. it is less readable
>
>
>
>>
>> Also, as you note, there are debatable design decisions in this particular
>> patch. There are already a couple of ways in which control knobs can be
>> attached to plgsql functions (i.e. custom GUCs and the comp_option stuff),
>> so why is this patch wanting to invent yet another fundamental mechanism?
>> And I'm not very happy about it imposing a new reserved keyword, either.
>>
>
> 1.
>
> custom GUC has not local scope - so it doesn't allow precious settings.
> With PRAGMA I have perfect control what will be impacted.
>
> #option has function scope
>
> 2. I'll not introduce a PRAGMA keyword just for this feature. We would to
> implement autonomous transactions. There was not any objection against this
> feature. The PRAGMA allows to share PL/SQL syntax and functionality.
>
>
>> A bigger-picture question is why we'd only provide such functionality
>> in plpgsql, and not for other uses of prepared plans.
>>
>
> It is out of scope of this patch.
>

The scope of this patch can be enhanced - but it is different task because
user interface should be different.

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>
>>
>> Lastly, it doesn't look to me like the test cases prove anything at all
>> about whether the feature does what it's claimed to.
>>
>
> I can enhance regress tests - currently there are not direct access to
> these attributes - so the tests can be indirect only :(
>
> Regards
>
> Pavel
>
>
>>
>> regards, tom lane
>>
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>