Re: pltcl.so patch - Mailing list pgsql-hackers

Okay, I've looked again at spi_exec and I believe I can fix the bug I
introduced and the memory leak. However, I have only looked quickly and not
made these most recent changes to the execp version nor to the plpython
code. Therefore I am not attaching a patch at the moment, just mentioning that
I've straightened this out in my brain a bit more.


On Wed, 25 Sep 2002, Nigel J. Andrews wrote:

> On 25 Sep 2002, Neil Conway wrote:
> 
> > "Nigel J. Andrews" <nandrews@investsystems.co.uk> writes:
> > > Yes, I do get the similar results.
> > > 
> > > A quick investigation shows that the SPI_freetuptable at the end of
> > > pltcl_SPI_exec is trying to free a tuptable of value 0x82ebe64
> > > (which looks sensible to me) but which has a memory context of
> > > 0x7f7f7f7f (the unallocated marker).
> > 
> > Attached is a patch against CVS HEAD which fixes this, I believe. The
> > problem appears to be the newly added free of the tuptable at the end
> > of pltcl_SPI_exec(). I've added a comment to that effect:
> > 
> >     /*
> >      * Do *NOT* free the tuptable here. That's because if the loop
> >      * body executed any SQL statements, it will have already free'd
> >      * the tuptable itself, so freeing it twice is not wise. We could
> >      * get around this by making a copy of SPI_tuptable->vals and
> >      * feeding that to pltcl_set_tuple_values above, but that would
> >      * still leak memory (the palloc'ed copy would only be free'd on
> >      * context reset).
> >      */
> 
> That's certainly where the fault was happening. However, that's where the
> original memory leak problem was coming from (without the SPI_freetuptable
> call). It could be I got that fix wrong and the extra calls you've added are
> the right fix for that. I'll take a look to see what I can learn later.
> 
> > At least, I *think* that's the problem -- I've only been looking at
> > the code for about 20 minutes, so I may be wrong. In any case, this
> > makes both memleak() and memleak(1) work on my machine. Let me know if
> > it works for you, and/or if someone knows of a better solution.
> 
> I'll have to check later.
> 
> > 
> > I also added some SPI_freetuptable() calls in some places where Nigel
> > didn't, and added some paranoia when dealing with statically sized
> > buffers (snprintf() rather than sprintf(), and so on). I also didn't
> > include Nigel's changes to some apparently unrelated PL/Python stuff
> > -- this patch includes only the PL/Tcl changes.
> 
> I dare say the plpython needs to be checked by someone who knows how to since I
> can well imagine the same nested call fault will exist there.
> 
> 
> 

-- 
Nigel J. Andrews