Re: Possible memory leak with SQL function?

Noah, this is the kind of memory leak I was referring to which would be
nice if valgrind could help with. I'm not sure exactly what that would look
like though, I've never tried writing support code for valgrind to deal
with custom allocators.

--
greg
On 16 Sep 2013 15:38, "Yeb Havinga" <yebhavinga(at)gmail(dot)com> wrote:

> On 2013-09-13 18:32, Robert Haas wrote:
>
>> On Thu, Sep 12, 2013 at 5:29 AM, Yeb Havinga <yebhavinga(at)gmail(dot)com>
>> wrote:
>>
>>> Is the following known behaviour, or should I put some time in writing a
>>> self contained test case?
>>>
>>> We have a function that takes a value and returns a ROW type. With the
>>> function implemented in language SQL, when executing this function in a
>>> large transaction, memory usage of the backend process increases.
>>> MemoryContextStats showed a lot of SQL function data. Debugging
>>> init_sql_fcache() showed that it was for the same function oid each time,
>>> and the oid was the function from value to ROW type.
>>>
>>> When the function is implemented in PL/pgSQL, the memory usage was much
>>> less.
>>>
>>> I'm sorry I cannot be more specific at the moment, such as what is 'much
>>> less' memory with a PL/pgSQl function, and are there as many SQL function
>>> data's as calls to the SQL function, because I would have to write a test
>>> case for this. I was just wondering, if this is known behavior of SQL
>>> functions vs PL/pgSQL functions, or could it be a bug?
>>>
>> It sounds like a bug to me, although I can't claim to know everything
>> there is to know about this topic.
>>
>> I spent some time writing a test case, but failed to make a test case
> that showed the memory difference I described upthread, in contrast, in the
> test below, the SQL function actually shows a smaller memory footprint than
> the plpgsql counterpart. This test case only demonstrates that in a long
> running transaction, calling sql or plpgsql functions causes increasing
> memory usage that is not released until after commit.
>
> callit.sql:
> ----------
> DO
> $$
> DECLARE b text;
> i int;
> BEGIN
> -- SELECT 'a' into b; -- memory constant
> i := fp('a'); -- memory increases
> -- i := fs('a'); -- memory increases but slow
> END;
> $$ LANGUAGE plpgsql;
> -------------
>
> sqlvsplpgsql.sql:
> -------------
> CREATE OR REPLACE FUNCTION fp (a text)
> RETURNS int
> AS $$
> DECLARE result int;
> BEGIN
> SELECT 10 INTO result;
> RETURN result;
> END;
> $$
> LANGUAGE plpgsql;
> CREATE OR REPLACE FUNCTION fs (a text)
> RETURNS int
> AS $$
> SELECT 10;
> $$
> LANGUAGE sql;
> \i callit.sql
> -------------
>
>
> rm /tmp/ff /tmp/ff2 ; cp callit.sql /tmp/ff ; cat /tmp/ff /tmp/ff >>
> /tmp/ff2; cat /tmp/ff2 /tmp/ff2 >> /tmp/ff; cat /tmp/ff /tmp/ff >>
> /tmp/ff2; cat /tmp/ff2 /tmp/ff2 >> /tmp/ff;cat /tmp/ff /tmp/ff >> /tmp/ff2;
> cat /tmp/ff2 /tmp/ff2 >> /tmp/ff;cat /tmp/ff /tmp/ff >> /tmp/ff2; cat
> /tmp/ff2 /tmp/ff2 >> /tmp/ff;cat /tmp/ff /tmp/ff >> /tmp/ff2; cat /tmp/ff2
> /tmp/ff2 >> /tmp/ff;cat /tmp/ff /tmp/ff >> /tmp/ff2; cat /tmp/ff2 /tmp/ff2
> >> /tmp/ff;cat /tmp/ff /tmp/ff >> /tmp/ff2; cat /tmp/ff2 /tmp/ff2 >> /tmp/ff
>
> psql -1 postgres -f /tmp/ff
>
> Then watch htop in another terminal.
>
>
> --
> Yeb Havinga
> http://www.mgrid.net/
> Mastering Medical Data
>
>
>
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