Explain Plan format
The DBMS_XPLAN format accepts a lot of options, which are not all documented. Here is a small recap of available information. The minimum that is displayed is the Plan Line Id, the Operation, and the...
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Testing Oracle SQL online
Want to test some DDL, a query, check an execution plan? You need only a browser. And you can copy-paste, or simply link, your test-case in a forum, a tweet, an e-mail, a tweet. Here is a small list...
View ArticleResult Cache: when *not* to use it
I encountered recently a case where result cache was incorrectly used, leading to high contention when the application encountered a peak of load. It was not a surprise when I’ve seen that the function...
View ArticleMultitenant, PDB, ‘save state’, services and standby databases
Creating – and using – your own services has always been the recommendation. You can connect to a database without a service name, though the instance SID, but this is not what you should do. Each...
View ArticleJAN18: Database 11gR2 PSU, 12cR1 ProactiveBP, 12cR2 RU
If you want to apply the latest patches (and you should), you can go to the My Oracle Support Recommended Patch Advisor. But sometimes it is not up-todate. For example, for 12.1.0.2 only the PSU is...
View Article12cR2 PDB archive
In 12.1 we had the possibility to unplug a PDB by closing it and generating a .xml file that describes the PDB metadata required to plug the datafiles into another CDB. In 12.2 we got an additional...
View ArticleServer process name in Postgres and Oracle
Every database analysis should start with system load analysis. If the host is in CPU starvation, then looking at other statistics can be pointless. With ‘top’ on Linux, or equivalent such as process...
View ArticleV$MYSTAT delta values
Here is a little script I use from time to time to look at V$MYSTAT values and displaying on one line a set of statistics with their delta value between two calls. The first script, _mystat_init.sql,...
View ArticleFull page logging in Postgres and Oracle
In my opinion, the volume of logging (aka redo log, aka xlog, aka WAL) is the most important factor for OLTP performance, availability and scalability, for several reasons: This is the only structure...
View Article(DESCRIPTION_LIST=(DESCRIPTION=(ADDRESS_LIST=(FAILOVER=YES)(LOAD_BALANCE=NO)
Do you have complex connection strings with DESCRIPTION_LIST, DESCRIPTION, ADDRESS_LIST, ADDRESS and a nice combination of FAILOVER and LOAD_BALANCE? You probably checked the documentation, telling you...
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18c Read Only Oracle Home
This is the big new feature of Oracle 18c about database software installation. Something that was needed for decades for the ease of software deployment. Piet de Visser raised this to Oracle a long...
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ODA Lite: What is this ‘odacli’ repository?
When ODA Lite was introduced, with ODA X6-2 S/M/L, and now with ODA x7-2 S/M, a new ‘odacli’ was there to manage it. It will probably replace the oakcli for ODA HA as well in the future. One big...
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PDB upgrade from 12c to 18c
Oracle 18c is out, in the Oracle Cloud, and the first thing I do with a new version is testing how long it takes to upgrade a previous version PDB by unplug/plug. Faster upgrade should be the benefit...
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A free persistent Google Cloud service with Oracle XE
In a previous post I’ve listed several free online services which run an Oracle XE so that you can test your SQL easily. You may want use Oracle XE further, with full access to the database and its...
View Article18c, Cloud First and Cloud Only features: think differently
Remember the times when the Oracle Software features were the same on all platforms? Where Oracle databases could be ported to any relevant platform? Where we were able to try any feature, freely, by...
View Article18c dbms_xplan note about failed SQL Plan Baseline
SQL Plan Baselines is a great feature for plan stability: you capture the plans that you accept. However, if the data model changes and the accepted plans cannot reproduce, the optimizer will come with...
View Article18c new Lost Write Protection
There are many layers between the Oracle Database pwrite() calls and the physical sector written on disk: filesystem, logical volume, SAN or NAS, with a lot of smart software running for...
View ArticleEnabled, Accepted, Fixed SQL Plan Baselines
When the documentation is not always clear, I prefer to build a test case to be sure about the behavior in different context and different versions. Here is a test on SQL Plan Management to show which...
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18c PDB switchover
In multitenant, the recovery and availability are at CDB level. But customers asked for a switchover at PDB level so Oracle has done that in 18c, based on refreshable PDBs. For this test I have two...
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Result cache invalidation caused by DML locks
In a previous post about Result Cache, I was using ‘set autotrace on’ in my session to see when the result cache hit saves the logical reads. I got a comment, by e-mail and with full test case,...
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