Oracle FAQ Your Portal to the Oracle Knowledge Grid
HOME | ASK QUESTION | ADD INFO | SEARCH | E-MAIL US
 

Home -> Community -> Usenet -> comp.databases.theory -> Re: Do log files demand serialization?

Re: Do log files demand serialization?

From: David Cressey <david_at_dcressey.com>
Date: Fri, 15 Feb 2002 07:32:00 GMT
Message-ID: <QP2b8.83695$Nq6.17014@petpeeve.ziplink.net>


> If it's any help, logs don't have to record the updates for a transaction
> contiguously. Each action in the AIJ log is keyed by transaction ID, and

IIRC, (and it's been a while since I studied the internals of this) Transaction ID's are assigned serially, at the inception of a transaction, but that isn't the serial order that the term "serializability" refers to, when we are talking about the ACID properties of transactions.

Consider the following scenario:

Transaction A starts, and gets assigned ID = 126. Transaction B starts, and gets assigned ID = 127.

Transaction B updates column X of Row Y of table Z.

Transaction B commits.
Transaction A updates column W of row Y of table Z. The value of column X delivered by transaction B is copied by this action.

Transaction A commits.

If you want to serialize these transactions, it's clear that B precedes A, and not vice versa.
The fact that A has the "earlier" ID than B is of no consequence.

How this applies to AIJ records is complicated, but it works.

--
Regards,
    David Cressey
    www.dcressey.com
"Kendall" <kendallwillets_at_yahooooo.com> wrote in message
news:u6p4n3ftfblo20_at_news.supernews.com...
Received on Fri Feb 15 2002 - 01:32:00 CST

Original text of this message

HOME | ASK QUESTION | ADD INFO | SEARCH | E-MAIL US