RE: Locking

From: Powell, Mark <mark.powell2_at_hp.com>
Date: Thu, 17 Nov 2011 19:58:53 +0000
Message-ID: <7C4BF3B32B80CC44AE37D31B172415937DD14D1247_at_GVW1337EXC.americas.hpqcorp.net>

Paul, the Oracle read consistency model relies on undo segments to keep before images of changed data and all rows returned by a query are at the same point in time. Readers to not block writers and writers do not block readers in Oracle by default.

See your Concepts and DBA Administration manuals sections on read consistency and undo management.

-----Original Message-----

From: oracle-l-bounce_at_freelists.org [mailto:oracle-l-bounce_at_freelists.org] On Behalf Of Paul Harrison Sent: Thursday, November 17, 2011 2:53 PM To: oracle-l_at_freelists.org
Subject: Locking

Hi All,

Let's say I have 2 sessions open... session one updates a table and does not commit and can view the new updated data. session 2 is able to read the old data. How can session 2 read the old data if session 1 has an exclusive write lock on the table. Exclusive lock happens when updating a table?

Thanks,
Paul

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http://www.freelists.org/webpage/oracle-l Received on Thu Nov 17 2011 - 13:58:53 CST