Re: Avoid memory leaks during base backups

Bharath Rupireddy <bharath(dot)rupireddyforpostgres(at)gmail(dot)com> writes:
> Postgres currently can leak memory if a failure occurs during base
> backup in do_pg_backup_start() or do_pg_backup_stop() or
> perform_base_backup(). The palloc'd memory such as backup_state or
> tablespace_map in xlogfuncs.c or basebackup.c or tablespaceinfo or the
> memory that gets allocated by bbsink_begin_backup() in
> perform_base_backup() or any other, is left-out which may cause memory
> bloat on the server eventually. To experience this issue, run
> pg_basebackup with --label name longer than 1024 characters and
> observe memory with watch command, the memory usage goes up.

> It looks like the memory leak issue has been there for quite some
> time, discussed in [1].

> 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. 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.

regards, tom lane