enq: TX – index contention – Oracle wait event

If you performed lot of DMLs (specially Deletes) on a table, you may have lots of empty leaf blocks in the associated indexes on that table. These empty leaf blocks are left in the b-tree structure AND attached to the freelist. On subsequent inserts, the process might need to split a block so it takes…

enq: TM – contention – Oracle wait event

Oracle acquires a table lock on a child table if it’s performing modifications on the primary key column in the parent table that’s referenced by the foreign key of the child table. And these locks on the child table are full table locks (TM) i.e. these locks aren’t restricted to any row but to the…

Oracle Wait Events

When writing posts on performance tuning I felt that there needs to be a my-version of description of Oracle Wait Events along with Access method and Process & Memory Architecture. Thus this series is to start the Oracle Wait events which are common in any Database Environment BUT has a lot of story. db file…

db file sequential reads – Oracle wait event

DB file sequential reads wait event comes under the User I/O wait class. In any busy system this is one of the most common wait event and normally appears in the top 5 wait events. In this post we’ll understand whats happening during this wait event. In simple words, Db file sequential reads wait event…