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Re: Concurrency

From: Mladen Gogala <mladen(dot)gogala(at)vmsinfo(dot)com>
To: Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>
Cc: "pgsql-novice(at)postgresql(dot)org" <pgsql-novice(at)postgresql(dot)org>
Subject: Re: Concurrency
Date: 2010-10-12 20:59:37
Message-ID: 4CB4CC39.8090800@vmsinfo.com (view raw or flat)
Thread:
Lists: pgsql-novice
Tom Lane wrote:
> Mladen Gogala <mladen(dot)gogala(at)vmsinfo(dot)com> writes:
>   
>> Where is the problem? The problem lies in the fact that the 2nd 
>> transaction should have only seen the changes committed before it has 
>> begun, ie, x=1.
>>     
>
> You might want to go reread this:
> http://www.postgresql.org/docs/9.0/static/transaction-iso.html#XACT-READ-COMMITTED
> If you don't like that behavior, you might want SERIALIZABLE mode
> instead.
>
> 			regards, tom lane
>   
No, it wasn't about liking or not liking, I was only trying to get to 
the bottom of this behavior. In particular, I translated the phrase " 
The search condition of the command (the WHERE clause) is re-evaluated " 
as the transaction restart and have fully expected the triggers to fire 
twice, which didn't happen.  I am comparing Postgres to Oracle, to find 
out where should I expect different behavior and where should I expect 
exactly the same behavior. So far, I must say, the changes aren't too 
big. One of the biggest is the lack of the %ROWCOUNT attribute with 
cursors and a different set of exceptions. Also, there is no 
DBMS_OUTPUT, I have to use RAISE NOTICE, which feels strange but does 
the trick. As a DBA, I should be able to help developers when they do 
run into problems. And they will.

-- 
 
Mladen Gogala 
Sr. Oracle DBA
1500 Broadway
New York, NY 10036
(212) 329-5251
http://www.vmsinfo.com 
The Leader in Integrated Media Intelligence Solutions




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