Re: Excessive memory usage in multi-statement queries w/ partitioning

Hi Julien,

Thanks for taking a look at this.

On Thu, Jul 4, 2019 at 6:52 PM Julien Rouhaud <rjuju123(at)gmail(dot)com> wrote:
> On Tue, May 28, 2019 at 6:57 AM Amit Langote wrote:
> > >> Maybe like the attached? I'm not sure if we need to likewise be concerned
> > >> about exec_sql_string() being handed multi-query strings.
>
> the whole extension sql script is passed to execute_sql_string(), so I
> think that it's a good thing to have similar workaround there.

That makes sense, although it is perhaps much less likely for memory
usage explosion to occur in execute_sql_strings(), because the scripts
passed to execute_sql_strings() mostly contain utility statements and
rarely anything whose planning will explode in memory usage.

Anyway, I've added similar handling in execute_sql_strings() for consistency.

Now I wonder if we'll need to consider another path which calls
pg_plan_queries() on a possibly multi-statement query --
BuildCachedPlan()...

> About the patch:
>
> - * Switch to appropriate context for constructing querytrees (again,
> - * these must outlive the execution context).
> + * Switch to appropriate context for constructing querytrees.
> + * Memory allocated during this construction is released before
> + * the generated plan is executed.
>
> The comment should mention query and plan trees, everything else seems ok to me.

Okay, fixed.

Attached updated patch. Thanks again.

Regards,
Amit