Обсуждение: Re: [HACKERS] Everything leaks; How it mm suppose to work?

>>
>
>Does it make sense to have a 'row' context which is released just before
>starting with a new tuple ? The total number or free is the same but they
>are distributed over the query and unused memory should not accumulate.
>I have seen backends growing to 40-60MB with queries which scan a very
>large number of rows.
>


I think this would be appropiate.

With regards from Maurice.

> >Does it make sense to have a 'row' context which is released just
> >before starting with a new tuple ? The total number or free is the
> >same but they are distributed over the query and unused memory should
> >not accumulate.
> >I have seen backends growing to 40-60MB with queries which scan a
> >very large number of rows.
> I think this would be appropiate.

It seems that the CPU overhead on all queries would increase trying to
deallocate/reuse memory during the query. There are lots of places in
the backend where memory is palloc'd and then left lying around after
use; I had assumed it was sort-of-intentional to avoid having extra
cleanup overhead during a query.

                     - Tom

Thomas G. Lockhart wrote:
>
> > >Does it make sense to have a 'row' context which is released just
> > >before starting with a new tuple ? The total number or free is the
> > >same but they are distributed over the query and unused memory should
> > >not accumulate.
> > >I have seen backends growing to 40-60MB with queries which scan a
> > >very large number of rows.
> > I think this would be appropiate.
>
> It seems that the CPU overhead on all queries would increase trying to
> deallocate/reuse memory during the query. There are lots of places in
> the backend where memory is palloc'd and then left lying around after
> use; I had assumed it was sort-of-intentional to avoid having extra
> cleanup overhead during a query.

This problem (introduced in 6.3) is already fixed by Bruce - will be
in 6.3.2

Vadim

Thomas G. Lockhart replies to Maurice:
> > >Does it make sense to have a 'row' context which is released just
> > >before starting with a new tuple ? The total number or free is the
> > >same but they are distributed over the query and unused memory should
> > >not accumulate.
> > >I have seen backends growing to 40-60MB with queries which scan a
> > >very large number of rows.
> > I think this would be appropiate.
>
> It seems that the CPU overhead on all queries would increase trying to
> deallocate/reuse memory during the query. There are lots of places in
> the backend where memory is palloc'd and then left lying around after
> use; I had assumed it was sort-of-intentional to avoid having extra
> cleanup overhead during a query.

This is exactly right. Destroying a memory context in the current
implementationis a very high overhead operation. Doing it once per row
would be a performance disaster.

-dg

David Gould            dg@illustra.com           510.628.3783 or 510.305.9468
Informix Software  (No, really)         300 Lakeside Drive  Oakland, CA 94612
 - Linux. Not because it is free. Because it is better.