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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 00:58:18
Message-ID: 87prfzakt1.fsf@news-spur.riddles.org.uk (view raw or flat)
Thread:
Lists: pgsql-hackers
>>>>> "Tom" == Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> writes:

 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...)

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

Yup, fails the same way on an --enable-cassert build of 8.3.7.

Without --enable-cassert it _appears_ to work, but this is presumably
just because the freed memory happens not to be being clobbered
immediately.

-- 
Andrew.

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