I had a question of a colleague to have a look at a statement that…
You can now download and have another look at the presentations used during the In-Memory…
I wouldn’t believe the bad XMLType performance statement given stated in Martin Preiss’ blog post,…
When you follow the Oracle in-memory / optimizer team, then you have probably seen this…
You all know that having more than 255 columns in a table is a Bad Thing ™ – and surprisingly you don’t even have to get to 255 to hit the first bad thing about wide tables. If you’ve ever wondered what sorts of problems you can have, here are a few:
February 8, 2015 I was recently contacted about an odd performance issue with a software product named TDM, where certain SQL statements submitted to an Oracle 9.2.x database required roughly 30 seconds to execute when a nearly instantaneous response was expected. The person who reported the issue to me provided a sample SQL statement that […]
I think the “mini-series” is a really nice blogging concept – it can pull together a number of short articles to offer a much better learning experience for the reader than they could get from the random collection of sound-bites that so often typifies an internet search; so here’s my recommendation for this week’s mini-series: a set of articles by Sayan Malakshinov a couple of years ago comparing the behaviour of Deterministic Functions and Scalar Subquery Caching.
A new version 4.21 of the XPLAN_ASH utility is available for download. I publish this version because it will be used in the recent video tutorials explaining the Active Session History functionality of the script.
This is mainly a maintenance release that fixes some incompatibilities of the 4.2 version with less recent versions (10.2 and 22.214.171.124).
As an extra however, this version now differentiates between general CPU usage and in-memory CPU usage (similar to 126.96.36.199 Real-Time SQL Monitoring). This is not done in all possible sections of the output yet, but the most important ones are already covered.
January is winding down and RMOUG Training Days 2015 is just around the corner, taking up much of my after work hours.
With that, we are going to discuss a great performance console in the EM12c cloud control- Cluster Cache Coherency.
In an earlier (not very serious) post about count(*) I pointed out how the optimizer sometimes does a redundant “bitmap conversion to rowid” when counting. In the basic count(*) example I showed this wasn’t a realistic issue unless you had set cursor_sharing to “force” (or the now-deprecated “similar”). There are, however, some cases where the optimizer can do this in more realistic circumstances and this posting models a scenario I came across a few years ago. The exact execution path has changed over time (i.e. version) but the anomaly persists, even in 188.8.131.52.
First we create a “fact” table and a dimension table, with a bitmap index on the fact table and a corresponding primary key on the dimension table: