> > > > In the latter, you have expanded the scope of the transaction; which, > > sometimes you might want to do. > > Yes, I might. But, I'd like to understand it so I do know when I might > or might not want to do it. Understanding is good. You need to read the documentation on transactions: http://www.postgresql.org/docs/7.4/interactive/tutorial-transactions.html and Concurrency control: http://www.postgresql.org/docs/7.4/interactive/mvcc.html > > Say I have a BEFORE INSERT trigger that does a table lock. When > is that lock released? At the end of the trigger? Or after the > INSERT has completed? At the end of the transaction. > > For example, say I want to set a column on the row I'm inserting based > on what's already in the table. So I lock the table in the trigger > and check the current status of the table and set the column based on > that current status. > > I want to make sure that between the time the trigger completes and > when the insert finally happens that another session can't also do an > insert and see the same table state. Again, reading the docs on concurrency control and transactions will answer these questions. > > > > -- > Bill Moseley > moseley@xxxxxxxx > > > ---------------------------(end of broadcast)--------------------------- > TIP 1: if posting/reading through Usenet, please send an appropriate > subscribe-nomail command to majordomo@xxxxxxxxxxxxxx so that your > message can get through to the mailing list cleanly
