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May 2017

Quick and dirty Pathfinder (or SQLT XPLORE)

The other day I was working on a SQL with an odd plan (JPPD with pushed predicate not on the driver table inside the view) when as a test I flipped OFE back one version and got the plan I was expecting, this is (one of) the typical use case(s) for Pathfinder or SQLT XPLORE.

I didn’t have a reproducible testcase and while creating it is always a good thing (IMHO), I was working in a lower environment that gave me a degree of freedom in testing things. I knew exactly which release to go from ( -> so I wrote a few lines of PL/SQL to implement a smaller Pathfinder. The idea was to let it run while I was working on a testcase to emulate the problem (and maybe run full blown Pathfinder on it).

12cR2 needs to connect with password for Cross-PDB DML

In a previous post, I explained that Cross-PDB DML, executing an update/delete/insert with the CONTAINERS() clause, seems to be implemented with implicit database links. Connecting through a database link requires a password and this blog post is about an error you may encounter: ORA-01017: invalid username/password; logon denied

Virtualizing Big Data in the Cloud


Interview with PeopleSoft Administrator Podcast: Cost-Based Optimizer Statistics in PeopleSoft

I recently recorded another interview with Dan Iverson and Kyle Benson for the PeopleSoft Administrator Podcast, this time about management of Cost-Based Optimizer Statistics in PeopleSoft systems.

Oracle Security Training

Yesterday I made a short video to talk about my two day class " How to Perform a Security audit of an Oracle database " and added the video to YouTube. This class is going to be delivered at a....[Read More]

Posted by Pete On 26/05/17 At 09:39 AM


Headline – if you don’t want to read the note – the /*+ parallel(N) */ hint doesn’t mean a query will use parallel execution, even if there are enough parallel execution server processes to make it possible. The parallel(N) hint tells the optimizer to consider the cost of using parallel execution for each path that it examines, but ultimately the optimizer will still take the lowest cost path (bar the odd few special cases) and that path could turn out to be a serial path.

The likelihood of parallelism appearing for a given query changes across versions of Oracle so you can be fooled into thinking you’re seeing bugs as you test new versions but it’s (almost certainly) the same old rule being applied in different circumstances. Here’s an example – which I’ll start off on

Joining Accenture Enkitec Group

I have accepted an offer by the Accenture Enkitec Group to join them starting next month. That unit is a kind of ‘special force’ inside the large Accenture Corporation with particular expertise in Oracle Database and Oracle Engineered Systems technology.

Although I feel quite a bit sad to leave Oracle after all those years, the opportunity to work together with all these bright people – you can see some of them here – outshines that largely </p />

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I was not in the beta program for Oracle database 12c release 2 but when I was discussing security changes in the new release with some people who were in the beta they told me that O7_DICTIONARY_ACCESSIBILITY and utl_file_dir parameters....[Read More]

Posted by Pete On 23/05/17 At 04:17 PM

255 Again!

There are so many things that can go wrong when you start using tables with more than 255 columns – here’s one I discovered partly because I was thinking about a client requirement, partly because I had a vague memory of a change in behaviour in 12c and Stefan Koehler pointed me to a blog note by Sayan Malakshinov when I asked the Oak Table if anyone remembered seeing the relevant note. Enough of the roundabout route, I’m going to start with a bit of code to create a table, stick a row in it, then update that row:

Oracle SuperCluster M7 SLOB LIO Tests vs Intel Xeon E5-2699 V4

Here are some SLOB LIO figures from a DB zone configured with 16 threads running on an Oracle SuperCluster M7 hardware. For comparison I've also included numbers from an Intel Xeon E5-2699 V4 CPU.

It makes sense to mention that this is not exactly a fair comparison -- a single SPARC M7 core has 8 threads associated with it so my zone is able to utilize a total of two SPARC M7 cores (16 threads total with 8 threads per core). E5-2699 V4 is currently top of the line Intel CPU core packed model with 22 cores. So we're comparing two SPARC M7 cores vs 16 E5-2699 cores. It does however help answer the question -- if you're running on a certain number of Intel cores what kind of performance can you expect when you move over to a heavy threaded M7 if you transfer your workload "as is"?