Subject: Re: logical replication syntax (was DROP SUBSCRIPTION,
 query cancellations and slot handling)
To: Peter Eisentraut <peter.eisentraut@2ndquadrant.com>,
 Tom Lane <tgl@sss.pgh.pa.us>
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Cc: Robert Haas <robertmhaas@gmail.com>,
 Michael Paquier <michael.paquier@gmail.com>,
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From: Petr Jelinek <petr.jelinek@2ndquadrant.com>
Message-ID: <5f6ad263-af87-2aee-b86b-8bf7e3260b73@2ndquadrant.com>
Date: Tue, 9 May 2017 10:39:09 +0200
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On 09/05/17 07:07, Peter Eisentraut wrote:
> On 5/8/17 23:23, Peter Eisentraut wrote:
>> The way this uses RESTRICT and CASCADE appears to be backwards from its
>> usual meaning.  Normally, CASCADE when dropping an object that is still
>> used by others will cause those other objects to be dropped.  The
>> equivalent here would be DROP REPLICATION SLOT + CASCADE would drop the
>> subscription.
>>
>> What we want to simulate instead is an "auto" dependency of the slot on
>> the subscription.  So you can drop the slot separately (subject to other
>> restrictions), and it is dropped automatically when the subscription is
>> dropped.  To avoid that, you can disassociate the slot from the
>> subscription, which you have implemented.
>>
>> I think we can therefore do without RESTRICT/CASCADE here.  If a slot is
>> associated with the subscription, it should be there when we drop the
>> subscription.  Otherwise, the user has to disassociate the slot and take
>> care of it manually.  So just keep the "cascade" behavior.
>>
>> Similarly, I wouldn't check first whether the slot exists.  If the
>> subscription is associated with the slot, it should be there.
> 
> Here is your patch amended for that.
> 

I am fine with this mechanism as well.

-- 
  Petr Jelinek                  http://www.2ndQuadrant.com/
  PostgreSQL Development, 24x7 Support, Training & Services


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