Re: [bug fix] Memory leak in dblink

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On 06/18/2014 07:29 PM, Tom Lane wrote:
> I wrote:
>> I do see growth in the per-query context as well. I'm not sure
>> where that's coming from, but we probably should try to find
>> out. A couple hundred bytes per iteration is going to add up,
>> even if it's not as fast as 8K per iteration. I'm not sure it's
>> dblink's fault, because I don't see anything in dblink.c that is
>> allocating anything in the per-query context, except for the
>> returned tuplestores, which somebody else should clean up.
>
> I poked at this example some more, and found that the additional
> memory leak is occurring during evaluation of the arguments to be
> passed to dblink(). There's been a comment there for a very long
> time suggesting that we might need to do something about that ...
>
> With the attached patch on top of yours, I see no leak anymore.

I can confirm that -- rock solid with 1 million iterations. I assume
that should not be back-patched though?

On a side note, while perusing this section of code:

8<-------------------------- at dblink.c:1176 --------------------------
/* make sure we have a persistent copy of the tupdesc */
tupdesc = CreateTupleDescCopy(tupdesc);

/* check result and tuple descriptor have the same number of columns */
if (nfields != tupdesc->natts)
ereport(ERROR,
(errcode(ERRCODE_DATATYPE_MISMATCH),
errmsg("remote query result rowtype does not match "
"the specified FROM clause rowtype")));

/* Prepare attinmeta for later data conversions */
sinfo->attinmeta = TupleDescGetAttInMetadata(tupdesc);

/* Create a new, empty tuplestore */
oldcontext =
MemoryContextSwitchTo(rsinfo->econtext->ecxt_per_query_memory);
sinfo->tuplestore = tuplestore_begin_heap(true, false, work_mem);
rsinfo->setResult = sinfo->tuplestore;
rsinfo->setDesc = tupdesc;
MemoryContextSwitchTo(oldcontext);
8<-------------------------- at dblink.c:1194 --------------------------

Shouldn't that CreateTupleDescCopy() happen in ecxt_per_query_memory?

Joe

- --
Joe Conway
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