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

On Mon, Dec 9, 2024 at 6:52 PM Amit Kapila <amit(dot)kapila16(at)gmail(dot)com> wrote:
>
> 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.

I agree to fix this as a separate patch.

Regards,

--
Masahiko Sawada
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