On Mon, Jul 13, 2026 at 03:37:54PM +0530, Amit Kapila wrote: > On Fri, Jul 10, 2026 at 10:22 AM Noah Misch <[email protected]> wrote: > > Fable 5 also wrote a lot more that neither it nor I confirmed by test case > > construction. I'm attaching the report; feel free to disregard. Finding-2 > > about default_transaction_read_only=on looks worth fixing if true, > > Agreed on Finding-2 as well. The issue is that the sequencesync > worker sets the value via SetSequence(), which calls > PreventCommandIfReadOnly("setval()") for non-temp sequences, so with > "default_transaction_read_only=on" on the subscriber the worker's > transaction is read-only and sequence sync fails and never reaches > READY. Table apply is unaffected only because > ExecSimpleRelationInsert() bypasses the executor's > ExecCheckXactReadOnly() path which is an undocumented, untested detail > rather than a stated guarantee. > > For a minimal backpatch, we can force the sequencesync worker to run > read-write (e.g. set default_transaction_read_only=off for its session > at startup) so it matches table apply, plus a test that sets the GUC > on the subscriber and verifies sequences reach READY. Separately, it's > worth documenting that logical replication apply is exempt from > default_transaction_read_only — it's a per-transaction default meant > to guard user writes and never makes the node physically read-only — > and making that exemption explicit for all logical replication workers > so tables no longer rely on the bypass. What do you think?
I wouldn't document those things. default_transaction_read_only just has the user write "BEGIN READ WRITE" instead of plain "BEGIN". Hence, it's more like an "are you sure?" prompt than a restrictive guard. It's no surprise that logical replication apply achieves the equivalent of BEGIN READ WRITE; I don't see that outcome as an exemption. If easy, I would have the worker do the C equivalent of "BEGIN READ WRITE" instead of actually changing the GUC. That makes it clear exactly which areas are overriding the default. But changing the GUC is fine.
