Oracle Database as our consultants live it every day: installation and patching, upgrades, RMAN backup and recovery, Data Guard, RAC, performance tuning, multitenant, licensing, and engineered systems such as ODA and Exadata.
By Franck Pachot . In my UKOUG OracleScene article on 12c online statistics and GTT I mentioned the following: A final note about those 12c changes in statistics gathering on GTT. In 11g the dbms_stats did a commit at the start. So if you did gather stats after the load, you had to set the GTT as ON COMMIT PRESERVE…
By Franck Pachot . Going to multitenant architecture is not a big change. The administration things (DBA, monitoring, backups) connect to the CDB and the application things connect to the PDB. Without the multitenant option, it is still recommended to go to the CDB architecture. The non-CDB is deprecated and the multitenant architecture brings interesting features. People often ask how…
By Franck Pachot . I was going to end this series with the previous post because the last access path available in Postgres is a bit special: a Seq Scan that returns only a sample of the rows, at random. However, it is the occasion to come back to the difference between random and sequential reads. I’m still working on…
By Franck Pachot . In the previous post we have seen the cheapest way to get one row, reading only one block from its physical location. But that’s the optimal case where the row has not moved. I’ll (nearly) conclude this series about access path with an update. ROWID in Oracle Here is the ROWID of one row in Oracle:…
By Franck Pachot . In the previous post we have seen how Postgres and Oracle finds the table row from the index entry. It uses the TID / ROWID. I’ll focus on this access path and I will have covered all Postgres access paths to table data. Oracle ACCESS BY ROWID I start with Oracle because we already have seen…
By Franck Pachot . I’ve published a few month ago an article in the UKOUG OracleScene magazine on Improving Statspack Experience: quick setup script, changing settings, filling Idle Events,etc. In the article, I used dbms_job to schedule the snapshots, because I have this script for years and never took the time to do it with dbms_scheduler. Thanks to Nicolas Jardot…
By Franck Pachot . There are little changes when you go to multitenant architecture and one of them is that you must connect with a service name. You cannot connect directly to a PDB with a beaqueath (aka local) connection. This post is about a workaround you may have in mind: create a common user and set a logon trigger…
By Franck Pachot . In the previous post we have seen a nice optimization to lower the consequences of bad correlation between the index and the table physical order: a bitmap, which may include false positives and then requires a ‘recheck’ of the condition, but with the goal to read each page only once. Now we are back to the…
By Franck Pachot . There are 4 models of Oracle Database Appliance with the new ODA X6 which is for the moment the latest ODA hardware version. One is similar to the previous X5-2 one, and 3 smaller ones known as ODA Lite. They are 1 year old already, here is a small recap of the differences and links to…
By Franck Pachot . In the previous post my queries were still reading the indexed column only, from a table which had no modifications since the last vacuum, and then didn’t need to read table pages: it was Index Only Scan. However, we often need more columns than the ones that are in the index. Here is the Index Scan…
By Franck Pachot . I realize that I’m talking about indexes in Oracle and Postgres, and didn’t mention yet the best website you can find about indexes, with concepts and examples for all RDBMS: http://use-the-index-luke.com. You will probably learn a lot about SQL design. Now let’s continue on execution plans with indexes. As we have seen two posts ago, an…
By Franck Pachot . Since X4 we can do Capacity on Demand on Exadata: disable some CPU cores to lower cost of Oracle Database licenses. Depending on the models, and the configuration, there are different minimums and here is a recap table about those. Here is the summary of Capacity on Demand minimum, maximum and increment. Those numbers come from the…
