Re: Memory leak in Pl/Python

Thank you for your answer, Tom.

I've tried code in your example and I still see an always growing
memory consumption (1Mb per second). As it was before, I do not see
growing memory if
I use 'select 1' query as argument of plpy.execute(). Table test does
not has any triggers or foreign keys, I just created it with script
you provided.

I think that is a leak because my system became use a swap file and
filnally OOM killer kills one of database process and database goes
into recovery mode. That is the problem...

On Sat, Jun 25, 2016 at 6:15 PM, Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> wrote:
> Andrey Zhidenkov <andrey(dot)zhidenkov(at)gmail(dot)com> writes:
>> I see memory consumption in htop and pg_activity tools.
>
> "top" can be pretty misleading if you don't know how to interpret its
> output, specifically that you have to discount whatever it shows as
> SHR space. That just represents the amount of the shared memory block
> that this process has touched so far in its lifetime; even if it appears
> to be growing, it's not a leak. That growth will stop eventually, once
> the process has touched every available shared buffer. RES minus SHR
> is a fairer estimate of the process's own memory consumption.
>
> I tried to reduce your example to a self-contained test case, thus:
>
> create extension if not exists plpythonu;
> create table test (test text);
> create or replace
> function test() returns bigint as $$
> plpy.execute("insert into test(test) values ('test')")
> return 1
> $$ language plpythonu;
> do $$
> begin
> for i in 1..10000000 loop
> perform test();
> end loop;
> end;
> $$;
>
> I do not see any significant leakage with this example. There is some
> memory growth, approximately 4 bytes per plpy.execute(), due to having to
> keep track of a subtransaction XID for each uncommitted subtransaction.
> That's not plpython's fault --- it would happen with any PL that executes
> each SQL command as a separate subtransaction, which is probably all of
> them other than plpgsql. And it really ought to be negligible anyway in
> any sane usage.
>
> It's possible that you're seeing some other, larger memory consumption;
> for instance, if there were triggers or foreign keys on the "test" table
> then perhaps there would be an opportunity for leakage in those.
> But without a self-contained test case or any indication of the rate
> of leakage you're seeing, it's hard to guess about the problem.
>
> regards, tom lane

--
Andrey Zhidenkov / Database developer
+79265617190/ andrey(dot)zhidenkov(at)gmail(dot)com

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