Обсуждение: perl garbage collector

Hi,
I have a stored procedure written in perl and I doubt that perl's
garbage collector is working :-(
after a lot of work, postmaster has a size of 1100 Mb and  I think
that the keyword "undef" has no effects.
Before tuning my procedure, does it exist a known issue, a workaround ?

--
Jean-Max Reymond
CKR Solutions Open Source
Nice France
http://www.ckr-solutions.com

On Jun 27, 2005, at 4:46 PM, Jean-Max Reymond wrote:

> Hi,
> I have a stored procedure written in perl and I doubt that perl's
> garbage collector is working :-(
> after a lot of work, postmaster has a size of 1100 Mb and  I think
> that the keyword "undef" has no effects.
> Before tuning my procedure, does it exist a known issue, a
> workaround ?

just because your application frees the memory doesn't mean that the
OS takes it back.   in other words, don't confuse memory usage with
memory leakage.


Vivek Khera, Ph.D.
+1-301-869-4449 x806

Jean-Max Reymond <jmreymond@gmail.com> writes:
> I have a stored procedure written in perl and I doubt that perl's
> garbage collector is working :-(
> after a lot of work, postmaster has a size of 1100 Mb and  I think
> that the keyword "undef" has no effects.

Check the PG list archives --- there's been previous discussion of
similar issues.  I think we concluded that when Perl is built to use
its own private memory allocator, the results of that competing with
malloc are not very pretty :-(.  You end up with a fragmented memory
map and no chance to give anything back to the OS.

            regards, tom lane

2005/6/28, Tom Lane <tgl@sss.pgh.pa.us>:
> Jean-Max Reymond <jmreymond@gmail.com> writes:
> > I have a stored procedure written in perl and I doubt that perl's
> > garbage collector is working :-(
> > after a lot of work, postmaster has a size of 1100 Mb and  I think
> > that the keyword "undef" has no effects.
>
> Check the PG list archives --- there's been previous discussion of
> similar issues.  I think we concluded that when Perl is built to use
> its own private memory allocator, the results of that competing with
> malloc are not very pretty :-(.  You end up with a fragmented memory
> map and no chance to give anything back to the OS.

thanks Tom for your advice. I have read the discussion but a small
test is very confusing for me.
Consider this function:

CREATE FUNCTION jmax() RETURNS integer
    AS $_$use strict;

my $i=0;
for ($i=0; $i<10000;$i++) {
        my $ch = "0123456789"x100000;
        my $res = spi_exec_query("select * from xdb_child where
doc_id=100 and ele_id=3 ");
}
my $j=1;$_$
    LANGUAGE plperlu SECURITY DEFINER;


ALTER FUNCTION public.jmax() OWNER TO postgres;

the line my $ch = "0123456789"x100000;   is used to allocate 1Mb.
the line my $res = spi_exec_query("select * from xdb_child where
doc_id=100 and ele_id=3 limit 5"); simulates a query.

without spi_exec_quer, the used memory in postmaster is a constant.
So, I think that pl/perl manages correctly memory in this case.
with spi_exec_query, postmaster grows and grows until the end of the loop.
Si, it seems that spi_exec_query does not release all the memory after
each call.
For my application (in real life) afer millions of spi_exec_query, it
grows up to 1Gb :-(



--
Jean-Max Reymond
CKR Solutions Open Source
Nice France
http://www.ckr-solutions.com

2005/6/28, Jean-Max Reymond <jmreymond@gmail.com>:
> For my application (in real life) afer millions of spi_exec_query, it
> grows up to 1Gb :-(

OK, now in 2 lines:

CREATE FUNCTION jmax() RETURNS integer
    AS $_$use strict;

for (my $i=0; $i<10000000;$i++) {
        spi_exec_query("select 'foo'");
}
my $j=1;$_$
    LANGUAGE plperlu SECURITY DEFINER

running this test and your postmaster eats a lot of memory.
it seems that there is a memory leak  in spi_exec_query :-(


--
Jean-Max Reymond
CKR Solutions Open Source
Nice France
http://www.ckr-solutions.com