Re: Things to consider during upgrade/migration

  • From: "Gogala, Mladen" <gogala.mladen@xxxxxxxxx>
  • To: loknath.73@xxxxxxxxx, Oracle L <oracle-l@xxxxxxxxxxxxx>
  • Date: Sat, 13 Nov 2021 15:33:38 -0500

On 11/13/2021 1:46 PM, Lok P wrote:

Hello Listers, With respect to havinga safe upgrade(say from 11.2 to 19C) or migration(From HP to Exadata) experience with minimal performance issues. Is there any guideline we should follow like settingup exadata system stats in case the targetdatabase is going to be exadata, Or verifying dictionary stats/table stats etc in a certain way. Want to know experts' views, if there are any such guidelines?



Hi Lok!

The old Itanic-based HP is very different from Exadata, approximately as much as Ford model T is different from Tesla model S. IT technology development has happened at slightly faster pace than the automotive technology development.  Also, Oracle 19c is very different from Oracle 11g. Your thinking should start from the nature of your application. Is that a data warehouse/reporting database type of application? Is it OLTP? Is it mixed mode? Do you need a dedicated service with preferred instance in case of an OLTP? Would mounting some instances in read mostly mode benefit you in any way? Should you make use of heat maps? You have that option with Exadata.

Exadata is primarily a data warehouse accelerator. Bloom filters on the storage nodes are meant to increase the speed of the full table scan. However, Exadata X8-2, the model that is mostly being sold these days, has some very interesting features like RDMA (direct memory access over the network) and persistent memory access, a form of extremely fast SSD which can tremendously speed up commit processing. That would be very important for an OLTP application. In other words, you will have to re-tune your application all over again. To quote the late Yogi Berra, "it's a deja vu all over again". The first thing to do is to get acquainted with your new wonder of technology and learn what can it do. Use fio or bonnie++ to measure IOPS. Use SLOB to see what Oracle can do with that. After that start testing the application in earnest, always having in mind that you might have to re-architect some pieces of it.

As far as system statistics is concerned, Oracle advises against that. I  once contacted Maria Colgan (aka "SQL Maria") directly with some questions about that advice and she explained to me why is that the official line. With Exadata, you will have Oracle Support on steroids. They will extend any help that they can give on a very short notice. They really do care about the Exadata customers.

Mladen Gogala
Oracle DBA
Tel: (347) 321-1217

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