Infrastructure at your Service

Category Archives: Oracle

Franck Pachot

Cloning a PDB from a standby database

By | Database management, Oracle | 5 Comments

By Franck Pachot . Great events like IOUG Collaborate is a good way to meet experts we know through blogs, twitter,etc. Yesterday evening, with nice music in the background, I was talking with Leighton Nelson about cloning PDB databases. Don’t miss his session today if you are in Las Vegas. The big problem with PDB cloning is that the source must be read-only. The reason is that it works like transportable tablespaces (except that it can…

 
Read More
Franck Pachot

RAC Attack! was another great success at C15LV

By | Operation systems, Oracle | No Comments

By Franck Pachot . The RAC Attack  – install a RAC in your own laptop – is a great success at Las Vegas. The idea is to help people follow the RAC Attack cookbook which is available at: http://en.wikibooks.org/wiki/RAC_Attack_-_Oracle_Cluster_Database_at_Home/RAC_Attack_12c/Hardware_Requirements It is a complex configuration and there is always problems to troubleshoot: get Virtual Box be able to run a 64-bits guest, and that might involve some BIOS settings be able to install VirtualBox, and we…

 
Read More
Franck Pachot

Dbvisit replicate REDO_READ_METHOD

By | Database management, Oracle | No Comments

By Franck Pachot . A frequent question about replication is the overhead in the source, because in a lot of cases the source is production. Dbvisit replicate comes with the possibility to do the minimum on the source: only the FETCHER process is there to read de redo logs and sends it to the MINE process wich can be on another server. But maybe even that – reading those critical online redo logs – is…

 
Read More
Franck Pachot

DataGuard wait events have changed in 12c

By | Database management, Oracle | 6 Comments

By Franck Pachot . There are several new features in 12c about Data Guard: cascaded standby, far sync instance. But there are also some architecture changes: new processes and new wait events. Here is an example of an AWR report of a LogXptMode=’SYNC’ DataGuard configuration in 11g – which means that the log_archive_dest is defined with: ‘LGWR SYNC AFFIRM’ That report comes from a period of time where the primary database was stuck because the…

 
Read More
Franck Pachot

Oracle tuning silver bullet: add an order by to make your query faster

By | Database management, Oracle | 11 Comments

By Franck Pachot . You have read all Cary Millsap work about Oracle database performance tuning. You know that there are no silver bullets. Reducing the response time requires a methodical approach in order to analyze the response time with the goal of eliminating all unnecessary work. But I’ll show something completly opposite here. A performance tuning silver bullet. Do more work in order to run it faster: just add an ORDER BY to your…

 
Read More
Franck Pachot

Index on SUBSTR(string,1,n) – do you still need old index?

By | Database management, Oracle | No Comments

By Franck Pachot . In a previous post I’ve shown that from 12.1.0.2 when you have an index on trunc(date) you don’t need additional index. If you need the column with full precision, then you can add it to the index on trunc(). A comment from Rainer Stenzel asked if that optimization is available for other functions. And Mohamed Houri has linked to his post where he shows that it’s the same with a trunc()…

 
Read More
Franck Pachot

Standard Edition on Oracle Database Appliance

By | Database management, Oracle | 2 Comments

By Franck Pachot . The Oracle Database Appliance is really interresting for small enterprises. It’s very good hardware for very good price. It’s capacity on demand licensing for Enteprise Edition. But small companies usually go to Standard Edition for cost reasons. Then does it make sense to propose only Enterprise Edition to the small companies that are interrested by ODA? Is ODA for small companies? My answer is definitely yes. Small companies can’t buy specific…

 
Read More
Franck Pachot

12c: shutdown abort a PDB?

By | Database management, Oracle | 3 Comments

By Franck Pachot . Can we shutdown abort a PDB? Let’s try: SQL> show con_id CON_ID —————————— 3SQL> shutdown abort; Pluggable Database closed. But is it really a shutdown abort? The shutdown abort we know in non-CDB – or in a CDB from CDB$ROOT – is used when the instance cannot checkpoint before closing the file. It leaves the files fuzzy. And shutdown abort crashes the instance – loosing all changes made in buffer cache…

 
Read More
Franck Pachot

Index on trunc(date) – do you still need old index?

By | Database management, Oracle | 6 Comments

By Franck Pachot . Sometimes we have to index on ( trunc(date) ) because a SQL statement uses predicate on it instead of giving a range from midnight to midnight. When you do that you probably keep the index on the column. That’s two indexes to maintain for DML. Do we need it? I’ll show a feature that appeared in 11.2.0.2 (info from oracle-l) so let’s set the optimizer to behave as before that feature….

 
Read More
Franck Pachot

Oracle compression, availability and licensing

By | Database management, Oracle | One Comment

By Franck Pachot . Various methods of table compression have been introduced at each release. Some require a specific storage system Some requires specific options. Some are only for static data. And it’s not always very clear for the simple reason that their name has changed. Name change for technical reasons (ROW/COLUMN STORE precision when a columnar compression has been introduced) or for marketing reason (COMPRESS FOR OLTP gave the idea that other – Exadata…

 
Read More