Re: documentation about explicit locking

From: Amit Langote <Langote_Amit_f8(at)lab(dot)ntt(dot)co(dot)jp>
To: Peter Eisentraut <peter(dot)eisentraut(at)2ndquadrant(dot)com>, Robert Haas <robertmhaas(at)gmail(dot)com>
Cc: Pg Hackers <pgsql-hackers(at)postgresql(dot)org>
Subject: Re: documentation about explicit locking
Date: 2018-07-31 01:27:24
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On 2018/07/31 5:27, Peter Eisentraut wrote:
> On 19/07/2018 06:17, Amit Langote wrote:
>> When playing with this, I observed that a less user-friendly error message
>> is emitted if multiple sessions race to create the same collation.
>> Session 1:
>> begin;
>> create collation collname (...);
>> Session 2:
>> create collation collname (...);
>> <blocks for lock on pg_collation>
>> Session 1:
>> commit;
>> Session 2:
>> ERROR: duplicate key value violates unique constraint
>> "pg_collation_name_enc_nsp_index"
>> DETAIL: Key (collname, collencoding, collnamespace)=(collname, 6, 2200)
>> already exists.
> You get the same behavior with for example CREATE FUNCTION or CREATE
> TYPE. I don't think we need to fix this specifically for CREATE COLLATION.

Hmm, yeah. Although fixing the race for CREATE COLLATION seems easier
than other cases due to the self-exclusive lock on the catalog, that
doesn't necessarily mean we have to.


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