Message-ID: <9afab261-94a7-3e58-f0fb-040e45f42aa5@enterprisedb.com>
Date: Thu, 23 Nov 2023 17:45:34 +0100
MIME-Version: 1.0
User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:102.0) Gecko/20100101
 Thunderbird/102.15.1
Subject: Re: undetected deadlock in ALTER SUBSCRIPTION ... REFRESH PUBLICATION
Content-Language: en-US
To: Amit Kapila <amit.kapila16@gmail.com>
Cc: PostgreSQL Hackers <pgsql-hackers@lists.postgresql.org>
References: <d291bb50-12c4-e8af-2af2-7bb9bb4d8e3e@enterprisedb.com>
 <CAA4eK1LHD3ZHqyK2GcSw=fqCPr26yP2GL9niQbY8ems68D1Z9A@mail.gmail.com>
 <8948e4a2-fec7-8a61-9ace-2537cee3ef6f@enterprisedb.com>
 <CAA4eK1Kj6THmgXZ98d8rxAJa+V1KGS79KgqVve5i0Oyn+=tbMw@mail.gmail.com>
 <69e9a1af-a315-8b05-0674-2cc53bf27682@enterprisedb.com>
 <CAA4eK1L4wWiFnhDYhGMv-M4GTR6Xg13xoaSjhUm+YzFaP3nxUQ@mail.gmail.com>
From: Tomas Vondra <tomas.vondra@enterprisedb.com>
In-Reply-To: 
 <CAA4eK1L4wWiFnhDYhGMv-M4GTR6Xg13xoaSjhUm+YzFaP3nxUQ@mail.gmail.com>
Content-Type: text/plain; charset=UTF-8
Content-Transfer-Encoding: 8bit
Archived-At: 
 <https://www.postgresql.org/message-id/9afab261-94a7-3e58-f0fb-040e45f42aa5%40enterprisedb.com>
Precedence: bulk


On 11/23/23 10:24, Amit Kapila wrote:
> On Wed, Nov 22, 2023 at 4:51 PM Tomas Vondra
> <tomas.vondra@enterprisedb.com> wrote:
>>
>> On 11/22/23 11:38, Amit Kapila wrote:
>>>
>>> Okay. IIUC, what's going on here is that the apply worker acquires
>>> AccessShareLock on pg_subscription to update rel state for one of the
>>> tables say tbl-1, and then for another table say tbl-2, it started
>>> waiting for a state change via wait_for_relation_state_change(). I
>>> think here the fix is to commit the transaction before we go for a
>>> wait. I guess we need something along the lines of what is proposed in
>>> [1] though we have solved the problem in that thread in some other
>>> way..
>>>
>>
>> Possibly. I haven't checked if the commit might have some unexpected
>> consequences, but I can confirm I can no longer reproduce the deadlock
>> with the patch applied.
>>
> 
> Thanks for the verification. Offhand, I don't see any problem with
> doing a commit at that place but will try to think some more about it.
> I think we may want to call pgstat_report_stat(false) after commit to
> avoid a long delay in stats.
> 

Makes sense.

> I haven't verified but I think this will be a problem in
> back-branches as well.
> 

Yes. I haven't tried but I don't see why backbranches wouldn't have the
same issue.

regards

-- 
Tomas Vondra
EnterpriseDB: http://www.enterprisedb.com
The Enterprise PostgreSQL Company