Re: Memory leak in WAL sender with pgoutput (v10~)

On Tue, Dec 10, 2024 at 2:17 AM Masahiko Sawada <sawada(dot)mshk(at)gmail(dot)com> wrote:
>
> On Mon, Dec 9, 2024 at 2:06 AM Amit Kapila <amit(dot)kapila16(at)gmail(dot)com> wrote:
> >
> > On Thu, Dec 5, 2024 at 2:56 PM Masahiko Sawada <sawada(dot)mshk(at)gmail(dot)com> wrote:
> > >
> > > >
> > > > I realized that this patch cannot be backpatched because it introduces a new
> > > > field into the public PGOutputData structure. Therefore, I think we may need to
> > > > use Alvaro's version [1] for the back branches.
> > >
> > > FWIW for back branches, I prefer using the foreach-pfree pattern
> > > Michael first proposed, just in case. It's not elegant but it can
> > > solve the problem while there is no risk of breaking non-core
> > > extensions.
> > >
> >
> > It couldn't solve the problem completely even in back-branches. The
> > SQL API case I mentioned and tested by Hou-San in the email [1] won't
> > be solved.
>
> True. There seems another place where we possibly leak memory on
> CacheMemoryContext when using pgoutput via SQL APIs:
>
> /* Map must live as long as the session does. */
> oldctx = MemoryContextSwitchTo(CacheMemoryContext);
>
> entry->attrmap = build_attrmap_by_name_if_req(indesc, outdesc, false);
>
> MemoryContextSwitchTo(oldctx);
> RelationClose(ancestor);
>
> entry->attrmap is pfree'd only when validating the RelationSyncEntry
> so remains even after logical decoding API calls.
>

We have also noticed this but it needs more analysis on the fix which
one of my colleagues is doing. I think we can fix this as a separate
issue unless you think otherwise.

--
With Regards,
Amit Kapila.