Re: ORA-01555; does update/select sequence matter?

From: John <jbradshaw777_at_yahoo.com>
Date: 13 Nov 2003 07:45:50 -0800
Message-ID: <f2f59d82.0311130745.27d15634@posting.google.com>

"Howard J. Rogers" <hjr_at_dizwell.com> wrote in message news:<3fb3226c$0$13498>
> SCN 1000 Do DML
> SCN 1001 Start Select
> SCN 1750 Encounter block with SCN 1000 which would usually be OK but
> there's a lock on one of the rows, so need rollback
> SCN 1751 Commit
>
> Either case, we need rollback.

I think this is where I made a mistake - exactly how SCN is generated and assigned. I thought
1. SCN is generated when DML is issued. All the data blocks affected will get this same SCN, say SCN100.
2. Later if the transaction end, all the data blocks get permanently stamped with that SCN100.
3. If the transaction is rollbacked, SCN100 basically is thrown away.

According to you and xho, ORACLE will generate one SCN for the DML and another for the 'commit'. Looks like I need to have a good read on exactly how ORACLE implements read consistency.

John Received on Thu Nov 13 2003 - 09:45:50 CST