On 23/01/17 17:19, Fujii Masao wrote:
> On Sat, Jan 21, 2017 at 1:39 AM, Petr Jelinek
> <petr.jeli...@2ndquadrant.com> wrote:
>> On 20/01/17 17:33, Jaime Casanova wrote:
>>> On 20 January 2017 at 11:25, Petr Jelinek <petr.jeli...@2ndquadrant.com> 
>>> wrote:
>>>> On 20/01/17 17:05, Fujii Masao wrote:
>>>>> On Fri, Jan 20, 2017 at 11:08 PM, Peter Eisentraut
>>>>> <peter.eisentr...@2ndquadrant.com> wrote:
>>>>>> On 1/19/17 5:01 PM, Petr Jelinek wrote:
>>>>>>> There were some conflicting changes committed today so I rebased the
>>>>>>> patch on top of them.
>>>>>>> Other than that nothing much has changed, I removed the separate sync
>>>>>>> commit patch, included the rename patch in the patchset and fixed the
>>>>>>> bug around pg_subscription catalog reported by Erik Rijkers.
>>>>>> Committed.
>>>>> Sorry I've not followed the discussion about logical replication at all, 
>>>>> but
>>>>> why does logical replication launcher need to start up by default?
>>>> Because running subscriptions is allowed by default. You'd need to set
>>>> max_logical_replication_workers to 0 to disable that.
>>> surely wal_level < logical shouldn't start a logical replication
>>> launcher, and after an initdb wal_level is only replica
>> Launcher is needed for subscriptions, subscriptions don't depend on
>> wal_level.
> But why did you enable only subscription by default while publication is
> disabled by default (i.e., wal_level != logical)? I think that it's better to
> enable both by default OR disable both by default.

That depends, the wal_level = logical by default was deemed to not be
worth the potential overhead in the thread about wal_level thread. There
is no such overhead associated with enabling subscription, one could say
that it's less work this way to setup whole thing. But I guess it's up
for a debate.

> While I was reading the logical rep code, I found that
> logicalrep_worker_launch returns *without* releasing LogicalRepWorkerLock
> when there is no unused worker slot. This seems a bug.

True, fix attached.

>     /* Report this after the initial starting message for consistency. */
>     if (max_replication_slots == 0)
>         ereport(ERROR,
>             errmsg("cannot start logical replication workers when
> max_replication_slots = 0")));
> logicalrep_worker_launch checks max_replication_slots as above.
> Why does it need to check that setting value in the *subscriber* side?
> Maybe I'm missing something here, but ISTM that the subscription uses
> one replication slot in *publisher* side but doesn't use in *subscriber* side.

Because replication origins are also limited by the
max_replication_slots and they are required for subscription to work (I
am not quite sure why it's the case, I guess we wanted to save GUC).

>     *  The apply worker may spawn additional workers (sync) for initial data
>     *  synchronization of tables.
> The above header comment in logical/worker.c is true?

Hmm not yet, there is separate patch for it in CF, I guess it got
through the cracks while rebasing.

  Petr Jelinek                  http://www.2ndQuadrant.com/
  PostgreSQL Development, 24x7 Support, Training & Services
From 1492ef374e3de60c112fe8e09225a788aa548755 Mon Sep 17 00:00:00 2001
From: Petr Jelinek <pjmodos@pjmodos.net>
Date: Mon, 23 Jan 2017 17:50:27 +0100
Subject: [PATCH] Release lock on failure to launch replication worker

 src/backend/replication/logical/launcher.c | 1 +
 1 file changed, 1 insertion(+)

diff --git a/src/backend/replication/logical/launcher.c b/src/backend/replication/logical/launcher.c
index d9ad66d..cb415f8 100644
--- a/src/backend/replication/logical/launcher.c
+++ b/src/backend/replication/logical/launcher.c
@@ -261,6 +261,7 @@ logicalrep_worker_launch(Oid dbid, Oid subid, const char *subname, Oid userid)
 	/* Bail if not found */
 	if (worker == NULL)
+		LWLockRelease(LogicalRepWorkerLock);
 				 errmsg("out of logical replication workers slots"),

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