On Tue, Feb 28, 2006 at 01:32:19AM -0500, Tom Lane wrote: > To do that requires not just that you have access to a backend's oldest > snapshot, but that you have access to *all* its active snapshots; > because such a transient tuple might be visible in some newer snap even > though it's too new for the oldest snap. Doing that will create very > significant problems of shared memory management, as well as performance > and locking issues. > > There's been some talk of distinguishing "global" and "within database" > xmin values, so that a long-lived transaction wouldn't interfere with > vacuuming tables in other databases that that xact couldn't possibly > access. That seems doable to me, but I think any finer-grained analysis > is probably going to be a net loss because of the distributed overhead > it'd impose on every transaction.
True, but we don't need this for every transaction, only long-running ones. And in most cases, it'd probably be safe to define 'long-running' in terms of minutes. Presumably, a mechanism similar to statement_timeout could be used to 'publish' the required state information after a given period of time. -- Jim C. Nasby, Sr. Engineering Consultant [EMAIL PROTECTED] Pervasive Software http://pervasive.com work: 512-231-6117 vcard: http://jim.nasby.net/pervasive.vcf cell: 512-569-9461 ---------------------------(end of broadcast)--------------------------- TIP 9: In versions below 8.0, the planner will ignore your desire to choose an index scan if your joining column's datatypes do not match
