Fix for memory leak in dblink

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From: Takahiro Itagaki <itagaki(dot)takahiro(at)oss(dot)ntt(dot)co(dot)jp>
To: pgsql-hackers(at)postgresql(dot)org
Subject: Fix for memory leak in dblink
Date: 2010-01-12 03:43:00
Message-ID: 20100112124300.C520.52131E4D@oss.ntt.co.jp
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There is a memory leak in dblink when we cancel a query during
returning tuples. It could leak a PGresult because memory used
by it is not palloc'ed one. I wrote a patch[1] before, but I've
badly used global variables to track the resource.

The attached is a cleaned up patch rewritten to use a tuplestore
(SFRM_Materialize mode) to return tuples suggested at [2]. Since
we don't return from the dblink function in tuplestore mode, we
can surely release the PGresult with a PG_CATCH block even on error.

Also, dblink_record_internal() and dblink_fetch() are rearranged
to share the same code to return tuples for code refactoring.

[1] http://archives.postgresql.org/pgsql-hackers/2009-06/msg01358.php
[2] http://archives.postgresql.org/pgsql-hackers/2009-10/msg00292.php

Regards,
---
Takahiro Itagaki
NTT Open Source Software Center

Attachment Content-Type Size
dblink-memleak_20100112.patch application/octet-stream 19.8 KB
From: Joe Conway <mail(at)joeconway(dot)com>
To: Takahiro Itagaki <itagaki(dot)takahiro(at)oss(dot)ntt(dot)co(dot)jp>
Cc: pgsql-hackers(at)postgresql(dot)org
Subject: Re: Fix for memory leak in dblink
Date: 2010-01-12 17:40:00
Message-ID: 4B4CB3F0.1000605@joeconway.com
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On 01/11/2010 07:43 PM, Takahiro Itagaki wrote:
> There is a memory leak in dblink when we cancel a query during
> returning tuples. It could leak a PGresult because memory used
> by it is not palloc'ed one. I wrote a patch[1] before, but I've
> badly used global variables to track the resource.
>
> The attached is a cleaned up patch rewritten to use a tuplestore
> (SFRM_Materialize mode) to return tuples suggested at [2]. Since
> we don't return from the dblink function in tuplestore mode, we
> can surely release the PGresult with a PG_CATCH block even on error.

Thanks -- I'll review this weekend.

Joe

From: Joe Conway <mail(at)joeconway(dot)com>
To: Takahiro Itagaki <itagaki(dot)takahiro(at)oss(dot)ntt(dot)co(dot)jp>
Cc: pgsql-hackers(at)postgresql(dot)org
Subject: Re: Fix for memory leak in dblink
Date: 2010-01-22 00:57:52
Message-ID: 4B58F810.7000700@joeconway.com
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On 01/11/2010 07:43 PM, Takahiro Itagaki wrote:
> There is a memory leak in dblink when we cancel a query during
> returning tuples. It could leak a PGresult because memory used
> by it is not palloc'ed one. I wrote a patch[1] before, but I've
> badly used global variables to track the resource.
>
> The attached is a cleaned up patch rewritten to use a tuplestore
> (SFRM_Materialize mode) to return tuples suggested at [2]. Since
> we don't return from the dblink function in tuplestore mode, we
> can surely release the PGresult with a PG_CATCH block even on error.
>
> Also, dblink_record_internal() and dblink_fetch() are rearranged
> to share the same code to return tuples for code refactoring.
>
> [1] http://archives.postgresql.org/pgsql-hackers/2009-06/msg01358.php
> [2] http://archives.postgresql.org/pgsql-hackers/2009-10/msg00292.php

This looks good to me. I'll commit in the next 24 hours if there are no
objections.

Thanks,

Joe