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September 2018

Case Study

A question about reading execution plans and optimising queries arrived on the ODC database forum a little while ago; the owner says the following statement is taking 14 minutes to return 30,000 rows and wants some help understanding why.

If you look at the original posting you’ll see that we’ve been given the text of the query and the execution plan including rowsource execution stats. There’s an inconsistency between the supplied information and the question asked, and I’ll get back to that shortly, but to keep this note fairly short I’ve excluded the 2nd half of the query (which is a UNION ALL) because the plan says the first part of the query took 13 minutes and 20 second and the user is worried about a total of 14 minutes.

My APEX 18.2 upgrade in a nutshell

As always, you should read the Installation/Upgrade manual from top to bottom before upgrading any piece of software, and be aware of all of the pre-requisites and processes.  But for me, my Application Express 18.2 upgrade was as simple as:

  • Download Application Express
  • Unzip to my target location
  • sqlplus / as sysdba
    • SQL> @apexins.sql SYSAUX SYSAUX TEMP /i/
  • Go to my ORDS installation
    • java -jar ords.war validate
  • sqlplus / as sysdba

And voila! A freshly upgraded Application Express in a matter of minutes…

Hacking for Skew

In my presentation to the UKOUG SIG yesterday “Struggling with Statistics – part 2” I described a problem that I wrote about a few months ago: when you join a fact table with a massively skewed distribution on one of the surrogate key columns to a dimension holding the unique list of keys and descriptions a query against a description “loses” the skew. Here’s an demo of the problem that’s a little simpler than the one in the previous article.

OpenWorld Monday…I’m so screwed

As I mentioned in a previous blog post, I whipped up a small Application Express application to let me plan out my Openworld activities. But there’s a small problem with being able to quickly and easily find thing based on the schedule…. There is too much to see!!!

I had a quick glance through the schedule just for Monday, and already I can see myself being very frustrated with all of the content that I am going to have miss out on, simply because it clashes with other content I’d like to see.

Oracle write consistency, bug, and scalable multi-thread de-queuing

A new blog post on the Databases at CERN blog:

A write consistency bug, how to see it with flashback query, and a scalable workaround.

https://db-blog.web.cern.ch/blog/franck-pachot/2018-09-oracle-write-consistency-bug-and-multi-thread-de-queuing

Oracle write consistency bug and multi-thread de-queuing

Column Group Catalog

I seem to have written a number of aricles about column groups – the rather special, and most useful, variant on extended stats. To make it as easy as possible to find the right article I’ve decided to produce a little catalogue (catalog) of all the relevant articles, with a little note about the topic each article covers. Some of the articles will link to others in the list, and there are a few items in the list from other blogs. There are also a few items which are the titles of drafts which have been hanging around for the last few years.

Correcting datatypes with minimal downtime

Just a quick post here by request of an attendee of the September Office Hours. I had a demo converting the data type of a primary key without losing data and with minimal impact to the availability of the database using DBMS_REDEFINITION.  You can see that video here

but here is the script used to run that demo. 

Upload large files to Oracle Cloud with the Object Storage REST API

A new blog post on the Databases at CERN blog:

Using the oci-curl() bash function to upload large files in multiple chunks to the OCI Object Storage service.

https://db-blog.web.cern.ch/blog/franck-pachot/2018-09-oracle-cloud-upload-large-files-through-object-store-rest-api

Oracle Cloud: upload large files through the Object Store REST API

Three Months at Microsoft

Time Flies when you’re having fun or when you’re crazy busy-  I’m unsure which is more true.

I just completed my first review as an employee at Microsoft and good news!  They’re going to keep me. </p />
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