Re: Incorrect CONTEXT reported for errors from parallel apply worker in logical replication

On Thu, 8 Oct 2026 at 13:23, Hayato Kuroda (Fujitsu)
<kuroda(dot)hayato(at)fujitsu(dot)com> wrote:
>
> I checked other examples in core, and parallel query seems to handle correctly.
> It has an attribute ParallelContext::error_context_stack which preserves an error
> context at that time, see CreateParallelContext(). When the parallel worker raises
> an ERROR, the leader backend can consume its message and raise it again, and at
> that time the error context is restored from the ParallelContext.
>
> I think the easiest fix is to use apply_error_context_stack for preserving the
> error context before entering the loop, attached patch implements the idea.

Thanks for the patch, the issue is resolved with your patch. One suggestion:
Can we add a comment saying the saved stack deliberately excludes
apply_error_callback. That would stop someone from "fixing" it back
later:
diff --git a/src/backend/replication/logical/worker.c
b/src/backend/replication/logical/worker.c
index 37b37500213..3d331c356a6 100644
--- a/src/backend/replication/logical/worker.c
+++ b/src/backend/replication/logical/worker.c
@@ -4088,7 +4088,7 @@ LogicalRepApplyLoop(XLogRecPtr last_received)
errcallback.callback = apply_error_callback;
errcallback.previous = error_context_stack;
error_context_stack = &errcallback;
- apply_error_context_stack = error_context_stack;
+ apply_error_context_stack = errcallback.previous;

> IIUC no contexts can be stacked at the begining of the worker, i.e.,
> apply_error_context_stack can be NULL in any case. So the global variable can be
> removed if we clean up more aggressively. I also felt the name can be changed,
> but it's retained for now because the variable has been exposed.
>
> BTW, I also checked the REPACK CONCURRENTLY, but it seemed to have the same issue
> as the parallel apply. I locally found a reproducer and wrote a fix patch,
> I can share here or another place.

I felt we can discuss here itself as the fix should be similar for
both the cases and reviewing also would be easier.

Regards,
Vignesh