Обсуждение: question about implementing XA-ish functions
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 actionsit takes need to be later committed or rolled back based on the containing transactions commital or not. Not havinglooked 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 rolledbackand rightly mark my work as committed or rolled back. Thoughts? -- Theo Schlossnagle http://omniti.com/is/theo-schlossnagle p: +1.443.325.1357 x201 f: +1.410.872.4911
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 actionsit takes need to be later committed or rolled back based on the containing transactions commital or not. Not havinglooked 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 orrolledback 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
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