Redo per transaction inconsistency when running SLOB

From: Paul Houghton <Paul.Houghton_at_uis.cam.ac.uk>
Date: Thu, 23 Apr 2020 11:28:19 +0000
Message-ID: <LNXP265MB0777807B1055950754E2F81DE6D30_at_LNXP265MB0777.GBRP265.PROD.OUTLOOK.COM>

We have some new hardware which seems slower from an IO perspective than the old hardware, so I downloaded SLOB to investigate, and ran it on two databases which are copies of each other. Both on RHEL7 OS with Oracle 12.2.0.1 and the April critical patch. Both are in archive log mode. Looking into the AWR, it seems the slower one on the new hardware is generating more redo per transaction than the old one. I set up SLOB identically in both databases (./setup.sh IOPS 8) and ran it identically (./runit.sh 8). The tablespace is a smallfile and I specified it's location, but otherwise I used the defaults. I set up the admin user as "sys/sys as sysdba" and for this run changed the run time to 900 seconds.

There are some differences in configuration. The slow one is supposed to be more like production than the faster one, so it has:

bigger buffers the log buffer is 10M as opposed to 5M in the faster one

uses huge pages, where the fast one doesn't

LOST_WRITE_PROTECT is NONE in both environments.

a physical standby database. The faster one doesn't There are applications running against these databases, but I can't see that there was any application SQL that would make this much difference.

I am looking in the load profile section of the AWR report that is generated. Redo size per transaction is 54K for the faster one, and 203k for the slower one, so about 4x as much. What could be causing this? I'd be grateful for some pointers as to where I can look to see what is causing the extra redo.

Thanks

PaulH

--
http://www.freelists.org/webpage/oracle-l

Received on Thu Apr 23 2020 - 13:28:19 CEST

This message: [ Message body ]
Next message: Jonathan Lewis: "Re: Redo per transaction inconsistency when running SLOB"
Previous message: Øyvind Isene: "Re: Automatic SSL certification renewal product"
Next in thread: Jonathan Lewis: "Re: Redo per transaction inconsistency when running SLOB"
Reply: Jonathan Lewis: "Re: Redo per transaction inconsistency when running SLOB"
Reply: Harel Safra: "Re: Redo per transaction inconsistency when running SLOB"
Maybe reply: Paul Houghton: "RE: Redo per transaction inconsistency when running SLOB"

Contemporary messages sorted: [ by date ] [ by thread ] [ by subject ] [ by author ]

Original text of this message