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Video : Virtual Columns in Oracle Database 11g Onward

In today’s video we’ll demonstrate how to use virtual columns, introduced in Oracle 11g.

The video is based on this article.

The star of today’s video is Scott Wesley of APEX fame. I think he’s into gardening too, because he has a blog about grass or something… </p />

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Optimizer Statistics Gathering – pending and history

By Franck Pachot

This was initially posted to CERN Database blog on Wednesday, 12 September 2018 where it seems to be lost. Here is a copy thanks to

Demo table

I create a table for the demo. The CTAS gathers statistics (12c online statistics gathering) with one row and then I insert more rows:

10:33:56 SQL> create table DEMO as select rownum n from dual;
Table DEMO created.
10:33:56 SQL> insert into DEMO select rownum n from xmltable('1 to 41');
41 rows inserted.
10:33:56 SQL> commit;
Commit complete.

The estimations are stale: estimates 1 row (E-Rows) but 42 actual rows (A-Rows)

Oracle database reliable message waits

This blog is about the oracle database wait event ‘reliable message’. It should be noted that normally, this should not be a prominent wait, and if it does so, the most logical cause would be something that is not working as it should, either by oversubscribing something or simply because of a bug.

The reliable message note on My Oracle Support provides a good description:

Oracle database processes and waiting long in the supermarket

Hopefully I got your interest by the weird name of this blogpost. This blogpost is about sensible usage of an Oracle database. Probably, there are a lot of blog posts like this, but I need to get this off my chest.

A quote any starwars fan would recognise is ‘I sense a disturbance in the force’. I do, and I have felt it for a long time. This disturbance is the usage of the number of connections for a database. Because of my profession, this is the oracle database, but this really applies to the server-side of any client/server server processor running on at least (but probably not limited to) intel Xeon processors.

The disturbance is the oversubscription or sometimes even excessive oversubscription of database connections from application servers, or any other means of database processes that acts as clients. This means this does not exclude parallel query processes, in other words: this applies to parallel query processes too.

19c tweak

There are times when an upgrade makes a big difference to performance because an enhancement to the optimizer code path changes the costing of a plan that was always possible, but badly costed. I noticed an example of this while testing the code in the email I mentioned in last month’s posting on the “Incremental Sort” that Postgres 13 can do. Here’s a model to create some data and demonstrate the principle – the code is a modified (reduced) version of the code published by Phil Florent describing the feature.

Why Why Why Why?

Here’s a little puzzle – and if you don’t see the answer almost immediately you did need to read this note. The question comes from a thread on the Oracle Groundbreakers’ Forum –

“Why I am getting 0020 instead of 2020 for below query?”

select to_char(to_date(sysdate,'dd-mm-yyyy'),'iyyy') from dual.

Instead of sysdate if I give date like ‘5-dec-2020’ it’s giving correct. Any ideas why iso value for sysdate year is coming as 0020?

Upgrade trivia

Sometimes it’s the little things that catch you out (perhaps only briefly) on an upgrade. Here’s one that came up on Oracle’s Groundbreakers Developers Community [sic] (who knows what it will be called this time next year and, while we’re at it, who can tell where the apostrophe(s) ought to go).

The problem was with a database trigger that had been doing home-grown auditing to catch any DDL changes to non-SYS objects. The code was quite simple:

Video : Convert CentOS to Oracle Linux

In today’s video we’ll demonstrate how to convert a CentOS installation to an Oracle Linux installation.

The video is based on this post.

The star of today’s video is Dan Norris, in a clip from a previous OpenWorld, which seems like a long distant memory now.



PS. I know I said there would be no more videos this year, but this was very much “of the moment”, so I thought it was worth doing.