Blog of Franck Pachot, Consultant at dbi services
Franck Pachot is Consultant at dbi services. He has 20 years of experience in Oracle databases. Through his expertise as a DBA, Oracle expert, data architect, and performance specialist, he is able to cover all database areas: architecture, data modeling, database design, tuning, operation, and training. Franck Pachot knows how to enable an efficient collaboration between the developers and the operational team when it comes to troubleshooting issues or performance tuning. He has passed the OCP certifications from 8i to 12c, is also Certified Expert for Oracle Database 11g Performance Tuning, and now achived the highest level of certification: Oracle Master Certified OCM 11g. Prior to joining dbi services, Franck Pachot was Oracle Consultant at Trivadis in Lausanne. Previously, he worked in several countries and environements, always as a consultant. Franck Pachot holds a Master of Business Informatics from the University of Paris-Sud. His branch-related experience covers Financial Services / Banking, Public Sector, Food, Transport and Logistics, Pharma, etc.
You are using an Oracle Enterprise Edition and thinking about downgrading to the Standard Edition? In this case, you must be sure that your applications are compatible. It's not something easy to check. Here are a few ideas.
With OMF datafiles, you don't manage the datafile names. But how do you set the destination when you want to move them to another mount point? Let's see how easy (and online) it works in 12c. And how to do it with minimal downtime in 11g.
Your datafiles have grown in the past but now you want to reclaim as much space as possible, because you are short on filesystem space, or you want to move some files without moving empty blocks, or your backup size is too large. ALTER DATABASE DATAFILE ... RESIZE can reclaim the space at the end of the datafile, down to the latest allocated extent.
When you load data in direct-path and have the NOLOGGING attribute set, you minimize redo generation, but you take the risk, in case of media recovery, to loose the data in the blocks that you've loaded. So you probably run a backup as soon as the load is done. But what happens if you have a crash, with media failure, before the backup is finish?
I encountered recently the situation but - probably because of a bug - the result was not exactly what I expected. Of course, before saying that it's a bug I need to clear any doubt about what I think is the normal situation. So I've reproduced the normal situation and I'm sharing it here in case someone wants to see how to handle it.
Recently, I described the Partial Join Evaluation transformation that appeared last year in Oracle 12c. I did it as an introduction for another transformation that appeared long time ago in 10.1.0.3 but was not used by default. And even in the latest Oracle 12c patchset 1 (aka 188.8.131.52.0) it is still not enabled. But it's there and you can use it if you set optimizer_features_enabled to 184.108.40.206.1 (that's not a typo!).
When an Oracle Database spends a high percentage of its DB time in User I/O, I usually check the wait event histograms in order to see if the storage system is working well. But today, with storage going to SSD, most I/O are less than 1 milliseconds and we have no details about those wait times.
Do you remember last year, when 12c arrived with multitenant, David Hueber warned us about the fact that a single PDB can, under certain conditions, generate a complete system downtime? We are beta testers and opened a SR for that. Now one year later the first patchset is out and obviously I checked if the issue was fixed. It's a patchset afterall, which is expected to fix issues before than bringing new features.
In a previous post I used X$KCCAGF to get more information about reclaimable archived logs in FRA, because there is a bug in standby (not opened) databases where archivelog deletion policy is ignored. I explained that the view V$RECOVERY_AREA_USAGE has only aggregated information about space reclaimable without the details about which files are reclaimable or not. Here I'll explain how I came to X$KCCAGF and I'll give the query to get all the detailed information that is hidden behind V$RECOVERY_AREA_USAGE.