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September 2019

Update restarts

Somewhere I think I’ve published a note about an anomaly that’s been bugging me since at least Oracle 10g – but if it is somewhere on the Internet it’s hiding itself very well and I can’t find it, though I have managed to find a few scripts on my laptop that make a casual reference to the side effects of the provlem. [Ed: a tweet from Timur Ahkmadeev has identified a conversation in the comments on an older post that could explain why I thought I’d written something about the issue.]

Anyway, I’ve decided to create some new code and write the article (all over again, maybe). The problem is a strange overhead that can appear when you do a simple but large update driving off a tablescan.

Extending in-lists

A well known “limitation” of Oracle is that you can only have 1000 elements within an IN-LIST style expression in your SQL predicates. I use the quotes because I’ve always found that if you are heading into the territory where you need more than 1000 items in an IN-LIST, then it is often indicative of something else being wrong. For example, if the code is backing a user interface, then where in the design phase did someone not go “Whoa…we are going to have 1000 select-able elements on the screen?”

In any event, you can find many tricks and techniques out there on the intertubes about how workaround this issue, such as:

Quiz Night

Upgrades cause surprises – here’s a pair of results from a model that I constructed more than 15 years ago, and ran today on 12.2, then modified and ran again, then ran on 11.2.0.4, then on 12.1.0.2. It’s very simple, I just create a table, gather stats, then update every row.

Speaker info for Perth, Australia

I have just got back from the Groundbreakers Latin America tour, and the travelling was made so much easier with the information provided by the organizers. So with the APAC tour coming up, I felt duty bound to give some hopefully useful information about my home town in Perth.

Flying in/out

There are two airport terminals in Perth. In times gone by, these were known as the Domestic and International terminals because, as the names suggest, domestic flights within Australia landed at one, and flights from overseas landed at the other. Hence locals will still refer to the terminals as “domestic” and “international”. However, due to all sorts of politics and bickering between airlines, times have changed.

Working with AWR: Old Statistics and Costs in Current Execution Plans

This is a blog about a little trap, into which it is easy to fall when analysing performance problems using ASH data and execution plans from AWR.
I will illustrate it with a real example taken from a production PeopleSoft system. A number of sessions were waiting on blocking locks.  I used ASH data to find statements running while holding a blocking lock.  That led me to a particular SQL ID and plan have value.

#eeeeee; border: 0px solid #000000; font-family: courier new; font-size: 100%; overflow: auto; padding-left: 4px; padding-right: 4px; width: 95%;">SQL_ID        SQL_PLAN_HASH_VALUE   ASH_SECS
------------- ------------------- ----------
29210
5st32un4a2y92 2494504609 10670
652mx4tffq415 1888029394 7030
artqgxug4z0f1 8450529 580

Truncate AWR tables (unsupported)

When WRH$ tables grow too large so that they cannot be purged

This is no supported, please look at the My Oracle Support notes for a supported way to purge AWR when going too big, like re-creating AWR (needs to start the database in restricted mode) or purging with the normal procedure (can be long as it runs a delete). And do not copy-paste my statements as this is just an example.

When some tables grow too large, the purge job does not work correctly (because some things like the partitioning are done at the end). Then SYSAUX grows. And worse: the next upgrade may take hours if it has to change something on the AWR tables.

Upgrade time

Here is an example of an upgrade from 11g to 19c which took hours. Here is how I open the upgrade logs with “less” for the Top-10 longest statement execution:

London March 2020: “Oracle Indexing Internals and Best Practices” and “Oracle Performance Diagnostics and Tuning” Seminars !!

It’s with great excitement that I announce I’ll finally be returning to London, UK in March 2020 to run both of my highly acclaimed seminars. The dates and registration links are as follows: 23-24 March 2020: “Oracle Indexing Internals and Best Practices” seminar – Tickets and Registration Link 25-26 March 2020: “Oracle Performance Diagnostics and […]

My OpenWorld!

Just a couple of weeks away, and my oh my, I am going to be busy at OpenWorld this year!

Of course, first cab off the block will be the OpenWorld swim! It it September and marvellously warm in San Fran, so what better year to come along and meet new friends, and get free coffee and donuts! Just grab a towel from the hotel and head down to the marina!

image

Register at the link below, so we know how many donuts to buy!!! Smile

Oracle Database 19c Automatic Indexing: Default Index Column Order Part I (Anyway Anyhow Anywhere)

The next thing I was curious about regarding Automatic Indexing was in which order would Oracle by default order the columns within an index. This can be a crucial decision with respect to the effectiveness of the index (but then again, may not be so crucial as well). Certainly one would expect the index column […]

Announcement: New “Oracle Indexing Internals and Best Practices” Webinar – 19-23 November 2019 in USA Friendly Time Zone

I’m very excited to announce a new Webinar series for my highly acclaimed “Oracle Indexing Internals and Best Practices” training event, running between 19-23 November 2019 !! Indexes are fundamental to every Oracle database and are crucial for optimal performance. However, there’s an incredible amount of misconception, misunderstanding and pure myth regarding how Oracle indexes function […]