Re: BUG #6785: Memory Leak in plpgsql

Hi,

On Monday, July 30, 2012 03:15:37 PM andervalbh(at)gmail(dot)com wrote:
> we recently had a memory exhaustion in the PostgreSQL server of the
> company, after a scan found a likely memory leak when using a plpgsql
> function.
> The problem occurred on an IBM x3400 server with 12G, CentOS 5.5 and
> PostgreSQL 9.1.4. The leak occurs when a variable declared type of a table
> column and when the
> column or the table ceases to exist.
> Follow the steps for the simulation:
>
> create table tbl_test
> (cod integer);
>
> CREATE OR REPLACE FUNCTION citgis.fct_test()
> RETURNS void AS
> $body$
> DECLARE
> v_cod tbl_test.cod%type;
> BEGIN
> return;
> END;
> $body$
> LANGUAGE 'plpgsql';
>
> drop table tbl_test;
>
>
> test=# select pg_backend_pid();
> pg_backend_pid
> ----------------
> 6465
>
> Initial memory
> ---------------------------------------------------------------------------
> --------------------------------------------- PID USER PR NI VIRT
> SWAP RES CODE DATA SHR S P %CPU %MEM TIME+ COMMAND
> 6465 postgres 15 0 1194m 1.2g 14m 4684 12m 3748 S 1 0.0 0.1
> 0:00.08 postgres: postgres test [local] idle
> 6465 postgres 15 0 1203m 1.2g 23m 4684 21m 3748 S 1 0.0 0.2
> 0:00.17 postgres: postgres test [local] idle
> 6465 postgres 15 0 1212m 1.2g 32m 4684 30m 3748 S 1 3.0 0.3
> 0:00.26 postgres: postgres test [local] idle
> 6465 postgres 16 0 1221m 1.2g 41m 4684 39m 3756 S 1 0.0 0.3
> 0:00.36 postgres: postgres test [local] idle
> ---------------------------------------------------------------------------
> ---------------------------------------------
I don't think youve found a memory leak here. I tested several thousand
iterations of this and the memory usage tops out a 93MB. What you see is
probably some memory fragmentation and that some copy-on-write page mappings
are only gradually brought into place.

Greetings,

Andres
--
Andres Freund http://www.2ndQuadrant.com/
PostgreSQL Development, 24x7 Support, Training & Services