Re: question about implementing XA-ish functions

This is perfect. It fires on both commit and rollback? And I can  
determine which?  The system I'm interfacing with has 2PC so it should  
be a pretty tight fit.  Thanks a ton Heikki!

--
Theo Schlossnagle (mobile)
http://omniti.com/is/theo-schlossnagle

On Dec 18, 2009, at 10:34 AM, Heikki Linnakangas <heikki.linnakangas@enterprisedb.com > wrote:

> Theo Schlossnagle wrote:
>> I'm trying to implement a function that has some XA like properties.
>>
>> Is it possible to write a postgres extension function that fires  
>> when called within a pg transaction... however, the actions it  
>> takes need to be later committed or rolled back based on the  
>> containing transactions commital or not.  Not having looked to  
>> deeply into this, I'm wondering if this is possible.  Naively, my  
>> first hookpoint would be something like:
>>
>> allocate something in the transactions memory context and register  
>> a cleanup.... do my work.
>>
>> when the transaction memory context is cleaned up, my cleanup  
>> handler fires, I detect whether the txn was committed or rolledback  
>> and rightly mark my work as committed or rolled back.
>
> See RegisterXactCallback(). And then there's the ResourceOwners, that
> you can use to register custom resources for cleanup.
>
> Of course, you'll never be able to make it atomic without 2PC. The
> callbacks are executed very soon after after the commit record has  
> been
> flushed to disk, so the window is small but it's there.
>
> -- 
>  Heikki Linnakangas
>  EnterpriseDB   http://www.enterprisedb.com