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Re: logical changeset generation v3 - comparison to Postgres-R change set format

From: Hannu Krosing <hannu(at)2ndQuadrant(dot)com>
To: Noah Misch <noah(at)leadboat(dot)com>
Cc: Markus Wanner <markus(at)bluegap(dot)ch>, Andres Freund <andres(at)anarazel(dot)de>, pgsql-hackers(at)postgresql(dot)org
Subject: Re: logical changeset generation v3 - comparison to Postgres-R change set format
Date: 2013-01-13 10:49:27
Message-ID: 50F29137.8050701@2ndQuadrant.com (view raw or flat)
Thread:
Lists: pgsql-hackers
On 01/13/2013 12:28 AM, Noah Misch wrote:
> [Catching up on old threads.]
>
> On Sat, Nov 17, 2012 at 03:40:49PM +0100, Hannu Krosing wrote:
>> On 11/17/2012 03:00 PM, Markus Wanner wrote:
>>> On 11/17/2012 02:30 PM, Hannu Krosing wrote:
>>>> Is it possible to replicate UPDATEs and DELETEs without a primary key in
>>>> PostgreSQL-R
>>> No. There must be some way to logically identify the tuple.
>> It can be done as selecting on _all_ attributes and updating/deleting
>> just the first matching row
>>
>> create cursor ...
>> select from t ... where t.* = (....)
>> fetch one ...
>> delete where current of ...
>>
>> This is on distant (round 3 or 4) roadmap for this work, just was
>> interested
>> if you had found any better way of doing this :)
> That only works if every attribute's type has a notion of equality ("xml" does
> not).  The equality operator may have a name other than "=", and an operator
> named "=" may exist with semantics other than equality ("box" is affected).
> Code attempting this replication strategy should select an equality operator
> the way typcache.c does so.
Does this hint that postgreSQL also needs an sameness operator
( "is" or "===" in same languages).

Or does "IS NOT DISTINCT FROM" already work even for types without
comparison operator ?

--------------
Hannu




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