Recently, I had a problem with accessing Active Session History being not fast enough on Oracle Database 11.2 and 12.1. Looking at the explain plan, wow, no doubt why: Accessing two fixed tables with TABLE ACCESS FULL and joining them with NESTED LOOP. This couldn’t have been “works as designed”, it would render gv$active_session_history nearly […]
Tag: Optimizer
Oracle SQL: Optimizing a WHERE predicate inequality with a Function Based Index
Intro Recently, on Oracle 11.2.0.3, I saw a join of three tables, using three times TABLE ACCESS FULL and HASH JOIN, without an obvious reason. During separating and understanding its components, the following scenario turned out to be the culprit. select * from CARDTEST where OBJECT_ID<DATA_OBJECT_ID; The optimizer is unable to calculate the cardinality of […]
R.I.P. Oracle Database 10g: “Oracle depends on humidity”
Or: “Why we should be happy about Adaptive Cursor Sharing” Premier Support for 10g R2 ended in July 2010, and Extended Support will end in July 2013, 11gR2 is widely used, and 12c is on the horizon. Maybe it’s time for writing a kind of obituary for my first Oracle love, and to spread a […]
Oracle 11.2: Cursor Mutex S wait event and too many (2^30) child cursors
Once again, there was a lesson to be learned about the Oracle RDBMS. The occaison was a direct upgrade from Enterprise Edition 10gR2 to EE 11gR2, the application was kept untouched for good reason. Problem After running the new version for two hours, everything became incredibly slow, and the CPU load on the DB server […]
Oracle 11g look-at’s
That’s a personal, quite unsorted list of (new or older) features I recently collected. All of them are things, I’d consider valuable or at least important to care about as soon as 11g is involved. It might be for system architecture knowledge, concept tasks, DBA hands-on, good-to-know or any other thing that my happen in […]
Oracle Explain Plans or Execution Plans: Guess or Reality?
Oracle finally desupported the rule-based optimizer with version 10g. Since 9i, users are good adviced to make themself familiar with the cost-based-optimizer (CBO). In order to understand what happens with your statement after parsing with CBO involved, and to be able to tune your queries, displaying, understanding and optimizing explain- or execution plans is essential. […]