Re: Add the ability to limit the amount of memory that can be allocated to backends.

Hi,

On 2023-10-24 09:39:42 +0700, Andrei Lepikhov wrote:
> On 20/10/2023 19:39, Stephen Frost wrote:
> Greetings,
> > * Andrei Lepikhov (a(dot)lepikhov(at)postgrespro(dot)ru) wrote:
> > > The only issue I worry about is the uncertainty and clutter that can be
> > > created by this feature. In the worst case, when we have a complex error
> > > stack (including the extension's CATCH sections, exceptions in stored
> > > procedures, etc.), the backend will throw the memory limit error repeatedly.
> >
> > I'm not seeing what additional uncertainty or clutter there is- this is,
> > again, exactly the same as what happens today on a system with
> > overcommit disabled and I don't feel like we get a lot of complaints
> > about this today.
>
> Maybe I missed something or see this feature from an alternate point of view
> (as an extension developer), but overcommit is more useful so far: it kills
> a process.

In case of postgres it doesn't just kill one postgres, it leads to *all*
connections being terminated.

> It means that after restart, the backend/background worker will have an
> initial internal state. With this limit enabled, we need to remember that
> each function call can cause an error, and we have to remember it using
> static PG_CATCH sections where we must rearrange local variables to the
> initial (?) state. So, it complicates development.

You need to be aware of errors being thrown regardless this feature, as
out-of-memory errors can be encountered today already. There also are many
other kinds of errors that can be thrown.

Greetings,

Andres Freund