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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 11:30:41
Message-ID: 50F29AE1.1070109@2ndQuadrant.com (view raw or flat)
Thread:
Lists: pgsql-hackers
On 01/13/2013 10:49 AM, Hannu Krosing wrote:
> 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 ?
Just checked - it does not, it still looks for "=" operator so it is 
just equality-with-nulls

How do people feel about adding a real sameness operator ?

Hannu


>
> --------------
> Hannu
>
>



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