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  1. Doc: Clarify the behavior of triggers/rules in a logical subscriber.

  1. clarifying trigger/rule behavior on logical replication subscribers

    Jonathan S. Katz <jkatz@postgresql.org> — 2023-06-06T13:58:14Z

    Hi,

While answering a question on "do triggers fire on a logical replication 
subscriber by default?" I tried to look up a reference to this behavior 
in the docs. There wasn't a clear reference point, but on the 
architecture page[1], I found this line that was closest to the answer:

"The apply process on the subscriber database always runs with 
session_replication_role set to replica, which produces the usual 
effects on triggers and constraints."

which assumes that the reader knows what the "usual effects" are.

Attached is a patch that disambiguates this.

Two additional items:

1. I do think this should be backpatched because it clarifies an 
existing behavior.

2. I don't know if we want to add a note about the trigger/rule behavior 
elsewhere in the logical replication section. I don't know if a reader 
would be expecting to find this in the "architecture" section.

Thanks,

Jonathan

[1] 
https://www.postgresql.org/docs/devel/logical-replication-architecture.html

  2. Re: clarifying trigger/rule behavior on logical replication subscribers

    vignesh C <vignesh21@gmail.com> — 2023-06-07T10:39:47Z

    On Wed, 7 Jun 2023 at 10:17, Jonathan S. Katz <jkatz@postgresql.org> wrote:
>
> Hi,
>
> While answering a question on "do triggers fire on a logical replication
> subscriber by default?" I tried to look up a reference to this behavior
> in the docs. There wasn't a clear reference point, but on the
> architecture page[1], I found this line that was closest to the answer:
>
> "The apply process on the subscriber database always runs with
> session_replication_role set to replica, which produces the usual
> effects on triggers and constraints."
>
> which assumes that the reader knows what the "usual effects" are.
>
> Attached is a patch that disambiguates this.
>

Thanks for the patch, one small change required, "literal>" should be
"<literal>":
+   enable triggers and rules on a table using the
+   <link linkend="sql-altertable"><command>ALTER TABLE</command></link> command
+   and the literal>ENABLE TRIGGER</literal> and <literal>ENABLE RULE</literal>

Regards,
Vignesh

  3. Re: clarifying trigger/rule behavior on logical replication subscribers

    Amit Kapila <amit.kapila16@gmail.com> — 2023-06-08T06:36:43Z

    On Wed, Jun 7, 2023 at 4:09 PM vignesh C <vignesh21@gmail.com> wrote:
>
> On Wed, 7 Jun 2023 at 10:17, Jonathan S. Katz <jkatz@postgresql.org> wrote:
> >
> > Hi,
> >
> > While answering a question on "do triggers fire on a logical replication
> > subscriber by default?" I tried to look up a reference to this behavior
> > in the docs. There wasn't a clear reference point, but on the
> > architecture page[1], I found this line that was closest to the answer:
> >
> > "The apply process on the subscriber database always runs with
> > session_replication_role set to replica, which produces the usual
> > effects on triggers and constraints."
> >
> > which assumes that the reader knows what the "usual effects" are.
> >
> > Attached is a patch that disambiguates this.
> >

I agree that it is a good idea to be explicit about this behavior. As
mentioned by you, it would be better to backpatch this. Also, I
thought about moving this to some other section like [1] but I think
we need to explain a bit about apply worker before providing this
specific information. So, the current place seems to be the best bet
considering the way current logical replication is documented.

[1] - https://www.postgresql.org/docs/devel/logical-replication-subscription.html

-- 
With Regards,
Amit Kapila.

  4. Re: clarifying trigger/rule behavior on logical replication subscribers

    Euler Taveira <euler@eulerto.com> — 2023-06-08T15:15:28Z

    On Thu, Jun 8, 2023, at 3:36 AM, Amit Kapila wrote:
> I agree that it is a good idea to be explicit about this behavior. As
> mentioned by you, it would be better to backpatch this. Also, I
> thought about moving this to some other section like [1] but I think
> we need to explain a bit about apply worker before providing this
> specific information. So, the current place seems to be the best bet
> considering the way current logical replication is documented.

I agree with this clarification in the suggested section. One small suggestion
is to avoid the word "replica", AFAICS it is not used in the logical
replication chapter; use "subscriber" instead. Another suggestion is to add
links to the exact ALTER TABLE ... ENABLE TRIGGER and ALTER TABLE ... ENABLE
RULE since we recently added it.


--
Euler Taveira
EDB   https://www.enterprisedb.com/

  5. Re: clarifying trigger/rule behavior on logical replication subscribers

    Peter Smith <smithpb2250@gmail.com> — 2023-06-21T00:03:09Z

    Hi.

I have made a patch v2.

This addresses the following:
- [1] Vignesh's review comment about unclosed SGML literal tag.
- [2] Euler's review comment about the word "replica"

But I did not address Euler's other review suggestion [2] about giving
direct links, because actually this patch text (without any direct
links) is almost identical with the existing
"session_replication_role" docs [3]. Instead of making the scope of
this patch bigger, if direct links are really wanted, I thought it is
better to have a separate patch for that which can address both docs.

~~~

I also tested/attached back-patches of the v2 patch for earlier
PostgreSQL versions. Actually, it turns out all the patches are the
same -- just named differently.

------
[1] https://www.postgresql.org/message-id/CALDaNm1fAaeOhdTts3LgXs_e1TPZke3-HqFA9b8ZjVXOM66H5Q%40mail.gmail.com
[2] https://www.postgresql.org/message-id/288747bd-911b-4370-8db2-6ecbb096037e%40app.fastmail.com
[3] https://www.postgresql.org/docs/devel/runtime-config-client.html

Kind Regards,
Peter Smith.
Fujitsu Australia

  6. Re: clarifying trigger/rule behavior on logical replication subscribers

    Peter Smith <smithpb2250@gmail.com> — 2023-07-27T02:16:50Z

    I created patches for this over a month ago, but then the thread went
quiet. Is there something more needed, or was it just accidentally
overlooked?

Should this be added to the commitfest?

------
Kind Regards,
Peter Smith.
Fujitsu Australia.

  7. Re: clarifying trigger/rule behavior on logical replication subscribers

    Laurenz Albe <laurenz.albe@cybertec.at> — 2023-07-27T05:28:22Z

    On Thu, 2023-07-27 at 12:16 +1000, Peter Smith wrote:
> I created patches for this over a month ago, but then the thread went
> quiet. Is there something more needed, or was it just accidentally
> overlooked?
> 
> Should this be added to the commitfest?

Yes, please add it to the commitfest.  That increases the likelyhood of
you patch not being forgotten.

Yours,
Laurenz Albe

  8. Re: clarifying trigger/rule behavior on logical replication subscribers

    Peter Smith <smithpb2250@gmail.com> — 2023-07-27T08:40:47Z

    It seems this was pushed already [1]. Sorry for the false alarm.

------
[1] https://github.com/postgres/postgres/commit/f5c446e3367527f9db1506d7c38d2f56e20950b6

Kind Regards,
Peter Smith.
Fujitsu Australia.