Re: [HACKERS] Create subscription with `create_slot=false` andincorrect slot name

On Wed, May 24, 2017 at 7:31 PM, Peter Eisentraut
<peter.eisentraut@2ndquadrant.com> wrote:
> On 5/23/17 02:33, Kuntal Ghosh wrote:
>>> The command succeed even if slot_name is invalid. That's because slot_name
>>> isn't validated. ReplicationSlotValidateName() should be called in
>>> parse_subscription_options() to avoid a pilot error. IMHO we should prevent
>>> a future error (use of invalid slot name).
>>>
>> +1. Since, slot_name can be provided even when create_slot is set
>> false, it should be validated as well while creating the subscription.
>
> This came up in a previous thread.  It is up to the publishing end what
> slot names it accepts.  So running the validation locally is incorrect.

That argument seems pretty tenuous; surely both ends are PostgreSQL,
and the rules for valid slot names aren't likely to change very often.

But even if we accept it as true, I still don't like the idea that a
DROP can just fail, especially with no real guidance as to how to fix
things so it doesn't fail.  Ideas:

1. If we didn't create the slot (and have never connected to it?),
don't try to drop it.

2. Emit some kind of a HINT telling people about ALTER SUBSCRIPTION ..
SET (slot_name = NONE).

3. ???

-- 
Robert Haas
EnterpriseDB: http://www.enterprisedb.com
The Enterprise PostgreSQL Company