On Tue, 2007-07-24 at 19:51 +0200, Luca Ferrari wrote:
> Now, for subtrans the xid is laizyly obtained, due to efficiency purposes. But
> in such way subtrans xid should be greater than each other xid of concurrent
> (main) transactions. If the subtrans inserts a record is the subtrans xid
> placed in xmin? Because in this case the xmin value makes the tuple invisible
> to every other concurrent transaction started with the parent one. Is this
> true or do the subtrans commit with the parent xid (in this case why the
> subtrans should have a xid?)? Ok, I'm bit confused here....
Visibility has nothing to do with subtransactions, so your worry is not
relevant. We judge visibility either at the start of each transaction
when in SERIALIZABLE mode, or we judge visibility at the start of each
statement when in READ COMMITTED (default) mode.
--
Simon Riggs
EnterpriseDB http://www.enterprisedb.com