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

From: Noah Misch <noah(at)leadboat(dot)com>
To: Hannu Krosing <hannu(at)2ndQuadrant(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-Rchange set format
Date: 2013-01-13 00:28:51
Message-ID: 20130113002851.GD16171@tornado.leadboat.com (view raw or flat)
Thread:
Lists: pgsql-hackers
[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.


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