Re: Do log files demand serialization?

From: David Cressey <>
Date: Fri, 15 Feb 2002 07:32:00 GMT
Message-ID: <QP2b8.83695$>

> 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.

    David Cressey
"Kendall" <> wrote in message
Received on Fri Feb 15 2002 - 08:32:00 CET

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