Re: Avoid memory leaks during base backups

On Mon, Sep 26, 2022 at 7:34 PM Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> wrote:
>
> > I'm proposing a patch that leverages the error callback mechanism and
> > memory context.
>
> This ... seems like inventing your own shape of wheel. The
> normal mechanism for preventing this type of leak is to put the
> allocations in a memory context that can be reset or deallocated
> in mainline code at the end of the operation.

Yes, that's the typical way and the patch attached does it for
perform_base_backup(). What happens if we allocate some memory in the
new memory context and error-out before reaching the end of operation?
How do we deallocate such memory?
Backup related code has simple-to-generate-error paths in between and
memory can easily be leaked.

Are you suggesting to use sigsetjmp or some other way to prevent memory leaks?

> I do not think that
> having an errcontext callback with side-effects like deallocating
> memory is even remotely safe, and it's certainly a first-order
> abuse of that mechanism.

Are you saying that the error callback might deallocate the memory
that may be needed later in the error processing?

--
Bharath Rupireddy
PostgreSQL Contributors Team
RDS Open Source Databases
Amazon Web Services: https://aws.amazon.com