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June 2019

Scalar Subquery Costing

A question came up on Oracle-l list-server a few days ago about how Oracle calculates costs for a scalar subquery in the select list. The question included an example to explain the point of the question. I’ve reproduced the test below, with the output from an 18.3 test system. The numbers don’t match the numbers produced in the original posting but they are consistent with the general appearance.

PFCLATK - Audit Trail Toolkit - Checksums

We have a toolkit called PFCLATK that is used in customer engagements to assist our customers to create comprehensive and useful audit trails for their databases. The toolkit is used in consulting engagements at the moment but will be adding....[Read More]

Posted by Pete On 06/06/19 At 03:08 PM

Hibernate for Oracle DBAs

Warning: any smart developer may feel sick when reading this ;)

I am not a developer, but I like to discuss with developers: share my side of the IT (the database that we want rock stable and durable) and listen to their side (the application that they want easy to maintain and evolve). And, as I like to understand what I’m talking about, I often need to test some snippets.

Many DBAs complain about Hibernate when they come upon the queries generated by a wrong mapping. They think it was designed to be bad (who would do that?). And they are convinced that JDBC and SQL are sufficient to build applications. Actually, many DBAs I have seen are persuaded that they understand everything about coding because they have written some ugly PERL scripts to automate their job. And that anything going beyond has the only goal to break the database.

Kscope Sunday will be awesome

Yeah yeah I know. What kind of dufus cut-pastes a giant image into their blog post. That would be ….. me Smile

But the reality is, there is just soooooo much going on this year on the Sunday before the “official” start of the Kscope conference, it was too hard to condense it into a few sentences. So I just dumped the image from the website, but you can read about it here.

It’s my first Kscope and it will be blast to be running a day of high quality but dirt cheap learning with Maria, Jeff, Steven and Blaine.

So long …

… and thanks for any Douglas Adams references.

I decided on Friday that after more than 31 years using the Oracle software and more than 37 years of being self-employed in the computer industry – not to mention a further 8 years being an enthusiastic amateur – the time had finally come for a change of pace.  As from 1st June 2019 I am retired.

Ignoring Hints

One of the small changes (and, potentially big but temporary, threats) in 18.3 is the status of the “ignore hints” parameter. It ceases to be a hidden (underscore) parameter so you can now officially set parameter optimizer_ignore_hints to true in the parameter file, or at the system level, or at the session level. The threat, of course, it that some of your code may use the hidden version of the parameter (perhaps in an SQL_Patch as an opt_param() option rather than in its hint form) which no longer works after the upgrade.

When Oracle Statistic Gathering times out.

When Oracle Statistic Gathering times out — I

This first part is about running manually, killing the job, and locking the stats

In a previous post, I explained how to see where the Auto Stats job has been running and timed out:

SYS.STATS_TARGET$

I got a case where it always timed out at the end of the standard maintenance window. One table takes many hours, longer than the largest maintenance window, it will always be killed at the end. And, because it stayed stale, and staler each day, this table was always listed first by the Auto Stat job. And many tables never got their chance to get their stats gathered for … years.

In that case, the priority is to gather statistics. That can be long. Then I run the job manually: