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Re: implementing asynchronous notifications PLEASE CONFIRM MY

From: David Gagnon <dgagnon(at)siunik(dot)com>
To:
Cc: pgsql-jdbc(at)postgresql(dot)org
Subject: Re: implementing asynchronous notifications PLEASE CONFIRM MY
Date: 2005-08-21 16:43:38
Message-ID: 4308AF3A.2070400@siunik.com (view raw or flat)
Thread:
Lists: pgsql-jdbc
Hi all,

  I have a java web application connected to a postgresql DB (of course 
:-)).  I create a bunch of cache in my web Application and I need 
postgresql to inform the application of row update and delete.  I think 
this is a common behavior when we cache data in the application and use 
stored procedure to update data. 

I saw this thread (See below) a while ago but I'm not sure a this is the 
best way to solve my problem.  I think there is 3 possibilities to solve 
this problem:

#1:  Having rules/trigger on update and delete that create 
notification.  On the java server I need a thread to read the 
notification and update the caches in the system accordingly.

#2: Having rules/trigger on update and delete that write a line into a 
table. On the java server I need a thread to read the table and update 
the caches in the system accordingly.

#3: Having rules/trigger on update and delete that call a CALLBACK 
function that goes directly to the server... and update the cache directly.

#4: Any other idea ?


For #1: Is that reliable? 100% full prove.  I must not loose 
notifications... because my cache wont be in synch

For #2:  Seem the best way to do it...  Is there a way to do it to 
reduce performance impact ?

For #3:  Don't think it's implemented yet ... am I wrong?


Thanks for your help pointing me the best implementation to solve my problem

Best Regards !

/David




Oliver Jowett wrote:

>David Gagnon wrote:
>
>  
>
>> I just read this thread. Wich seems really interesting.  Is there an
>>example on how to use Async Notifies?  I look at it a couple of months
>>ago and found it not sufficient for my needs.  I need to implement a
>>notification mechanism to clear data from caches in my application on
>>data update.
>>
>>Is this change allow me to do that .. ?  That will be so nice :-)
>>
>>If yes it's that possible to get a small example on how to use it.
>>    
>>
>
>Basically, you can now call PGConnection.getNotifications() and get
>results without having to submit a dummy query first.
>
>You will still need an application-level loop that periodically calls
>it, though. Also, it's not guaranteed to give you notifications: you
>must be not in a transaction (this is server-side behaviour), and you
>must be using a Socket implementation that implements available() (SSL
>connections may not do this).
>
>-O
>
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