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Re: EXPLAIN, utility statement parameters, and recent plpgsql changes

From: Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>
To: Dimitri Fontaine <dfontaine(at)hi-media(dot)com>
Cc: pgsql-hackers(at)postgreSQL(dot)org
Subject: Re: EXPLAIN, utility statement parameters, and recent plpgsql changes
Date: 2010-01-14 19:39:21
Message-ID: 27812.1263497961@sss.pgh.pa.us (view raw or flat)
Thread:
Lists: pgsql-hackers
Dimitri Fontaine <dfontaine(at)hi-media(dot)com> writes:
> Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> writes:
>> This works well enough for regular DML statements, but it falls down for
>> EXPLAIN which is a utility statement, because *parse analysis of utility
>> statements doesn't do anything*.  EXPLAIN actually does the parse
>> analysis of its contained statement at the beginning of execution.
>> And that is too late, in the scenario Pavel exhibited.  Why is it too
>> late?  Because SPI_cursor_open_internal() intentionally "freezes" the
>> ParamListInfo struct after doing initial parsing: what it copies into
>> the cursor portal is just a static list of data values without the
>> parser hooks (see copyParamList).

> Would it make any sense for this function to get to call the hook in the
> case a utility statement is being processed?

Well, the point of the hook is to change the results of parse
transformation, so just calling it doesn't do much --- you have to apply
the whole parse analysis process, *and keep the resulting tree*.

			regards, tom lane

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