Date: Wed, 12 Apr 2006 09:19:18 +0200
To: "Jim C. Nasby" <jnasby@pervasive.com>,
	"C Storm" <christian.storm@gmail.com>
Subject: Re: pgmemcache
Cc: pgsql-performance@postgresql.org
References: <1144135482.063425.33380@z34g2000cwc.googlegroups.com>
	<20060411225515.GZ49405@pervasive.com>
From: PFC <lists@peufeu.com>
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	It would be nice to have ON COMMIT triggers for this use.

	However you can emulate ON COMMIT triggers with a modification of the  
memcache update process :

	- A standard trigger sends the data to update to memcache
	- The trigger also sends the PID
	- Instead of being used immediately, this data is kept in a buffer
	- Notify is issued

	On commit :
	- postgres sends the NOTIFY signal
	- the memcache updater reads the NOTIFY (which embeds the PID I believe)  
; it finds the buffered data sent above and uses it to update memcached

	On rollback :
	- Interesting problem ;)))

	OK, it's a kludge. When can we get ON COMMIT triggers ?


> On Tue, Apr 04, 2006 at 12:24:42AM -0700, C Storm wrote:
>> I was wondering if anyone on the list has a successful installation of
>> pgmemcache running
>> that uses LISTEN/NOTIFY to signal a successfully completed transaction,
>> i.e., to get around the fact
>> that TRIGGERS are transaction unaware.  Or perhaps any other
>> information regarding a successful
>> deployment of pgmemcache.
>
> The problem with attempting that is that you'd have a window between
> transaction commit and when the cache was invalidated. If that's
> acceptable then it shouldn't be too difficult to set something up using
> LISTEN/NOTIFY like you describe.