RE: Original design approach to Oracle REDO Logs
Date: Thu, 17 Jun 2021 16:11:23 -0400
Message-ID: <63cf01d763b4$f2e36190$d8aa24b0$_at_rsiz.com>
While I agreed with what JL wrote, IF we knew how fast processors are now, then an update all rows query might compare the block images on the fly and not write the blocks where all the rows in a block were updated to the same value so that the actual block image resulting from the update didn’t need to be written.
Off the top of my head I *think* that would work and be efficient, but I am not engaged enough to ponder possible edge cases. But I *think* you have all the information you need in hand at commit time to flag blocks to *not* bother writing. If the buffer had to flush along the way before the commit, they would already be in the redo stream, but with the massive memory now available a private redo thread might be able to handle it both correctly and efficiently.
I really like Oracle’s redo model though. Someone once put it to me thusly: Everything Bill Bridge starts ends up in checkmate. (Meaning Bill wins.) Making sure the bucket has no leaks was definitely priority number one.
From: oracle-l-bounce_at_freelists.org [mailto:oracle-l-bounce_at_freelists.org] On Behalf Of Jonathan Lewis
Sent: Thursday, June 17, 2021 10:16 AM
Mike,
I don't think you can ask about hypothetical strategies for the redo log before stating what you think the purpose of the database should be.
If you expect the database to be the reference of last resort for the correctness and (immediate) consistency of the data then you might like a different strategy from someone who thinks the database is some sort of record of evolution of the data that allows the current version of the data to be re-imaged by a client.
Regards
Jonathan Lewis
On Thu, 17 Jun 2021 at 13:55, Michael D O'Shea/Woodward Informatics Ltd <woodwardinformatics_at_strychnine.co.uk> wrote:
Chaps, request for opinions/discussion/feedback .....
Question: If Oracle were written today, would the same strategy behind the "redo log" be adopted.
An example .... for a table of 10,000,000 rows, and a contrived piece of DML
update someTable
set someColumn1 = 1.234
that "updated" all the rows
but where someColumn1 was only updated to 1.234 for 6 rows as the remaining 10,000,000 - 6 rows were already 1.234
Should (assuming just DML and also just the basic data types, number, varchar2, date, ... ) the redo log
There is a considerable movement to event streaming technology such as Kafka to (indirectly) drive data change events to downstream and dependent systems (in Oracle assumably by polling the redo log file, or maybe some LogMiner interface .. I don't know the detail) in databases that include Oracle, MongoDB (referred to as Change Streams), and many more.
My "ask" focuses more on "just the database" interoperability with the remainder of what is often a large tech stack, and not the original design decision around redo logs for data recovery.
Mike
To: ORACLE-L (oracle-l_at_freelists.org)
Subject: Re: Original design approach to Oracle REDO Logs
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Received on Thu Jun 17 2021 - 22:11:23 CEST