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Re: doubt with pg_dump and high concurrent used databases

From: Pablo Alcaraz <pabloa(at)laotraesquina(dot)com(dot)ar>
To: pgsql-performance(at)postgresql(dot)org
Subject: Re: doubt with pg_dump and high concurrent used databases
Date: 2007-11-25 22:37:45
Message-ID: 4749F939.7090107@laotraesquina.com.ar (view raw or flat)
Thread:
Lists: pgsql-performance
Tom Lane wrote:
> "Peter Childs" <peterachilds(at)gmail(dot)com> writes:
>   
>> On 25/11/2007, Erik Jones <erik(at)myemma(dot)com> wrote:
>>     
>>>> Does the pg_dump create this kind of "consistent backups"? Or do I
>>>> need to do the backups using another program?
>>>>         
>>> Yes, that is exactly what pg_dump does.
>>>
>>>       
>> Yes so long as you are using transactions correctly. Ie doing a begin before
>> each invoice and a commit afterwards if your not bothering and using auto
>> commit you *may* have problems.
>>     
>
> I think you need to qualify that a bit more.  What you're saying is that
> if an application has consistency requirements that are momentarily
> violated during multi-statement updates, and it fails to wrap such
> updates into a single transaction, then pg_dump could capture one of the
> intermediate states.  That's true, but it's hardly pg_dump's fault.
> If there were a system crash partway through such a sequence, the
> consistency requirements would be violated afterwards, too.
>
>   

Agree. In my case I define "consistent database state" like the state 
the database has when the program that use it is stopped normally and 
without errors. In this "state" the program starts without troubles and 
"everything looks fine". I believe this behavior is because all the 
inserts and updates are made using transactions. Another things will be 
a bug, it ll be fixed and it ll not be pg_dump fault.

So if pg_dump can capture a "consistent state" with all the data until 
the start time, without all the pending open transaction updates/inserts 
in the same way that I did when I stopped the program before start 
pg_dump, for me is usefull and enough to solve my problem.

Thanks to all!

Pablo

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