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Re: TupleTableSlot API problem

From: Andrew Gierth <andrew(at)tao11(dot)riddles(dot)org(dot)uk>
To: Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>
Cc: pgsql-hackers(at)postgresql(dot)org
Subject: Re: TupleTableSlot API problem
Date: 2009-03-30 00:29:29
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Lists: pgsql-hackers
>>>>> "Tom" == Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> writes:

 >> For example, given some function foo(out a text, out b text) returning
 >> setof record, the query select t.a, t from foo() t; follows the
 >> sequence of events you describe, but it doesn't fail because
 >> slot-> tts_shouldFree is false, so the original minimaltuple isn't
 >> freed.

 Tom> Yeah, good point.  However I think that you could still get a
 Tom> failure.  The cases where a slot might contain a minimal tuple
 Tom> are generally where we are reading out of a tuplestore or
 Tom> tuplesort object, and all you have to do to get it to be a
 Tom> palloc'd mintuple is to make the test case big enough so the
 Tom> tuplestore has dumped to disk.  (Now that I think about it, I
 Tom> failed to try scaling up the test cases I did try...)

Aha; and indeed if you use select t.a, t from func() t; where the
function returns a set larger than work_mem, it does indeed fail
messily (against my -O0 --enable-cassert HEAD I just get corrupted
values for t.a, though, rather than an error). I'll try and reproduce
that on a back branch...


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Subject: Re: TupleTableSlot API problem
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