ORA-00001 unique constraint (%s.%s) violated

Cause: An UPDATE or INSERT statement attempted to insert a duplicate key. For Trusted Oracle configured in DBMS MAC mode, you may see this message if a duplicate entry exists at a different level. Action: Either remove the unique restriction or do not insert the key.

row cache lock – Oracle Wait Event

The Row Cache or Data Dictionary Cache is a memory area in the shared pool that holds data dictionary information to reduce physical I/O on the data dictionary tables. The row cache lock is used primarily to serialize changes to the data dictionary and is waited on when a lock on a data dictionary cache…

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…

12c New Features – Invisible Columns

There can be several situations where you want to test the impact of dropping a column from a table, till 11gR2 Oracle provided an option to mark a column as UNUSED before dropping a column, and do ALTER TABLE … DROP UNUSED COLUMNS at a later time but marking a column UNUSED is a irreversible…

Flashback PDB in Oracle 12cR2

After the introduction of multitenant architecture with Oracle 12cR1, the flashback database feature became irrelevant as it was limited to the root container which resulted in affecting all the PDBs associated with that root container. But with the new release 12cR2, flashback now supports pluggable databases as well. Now we’ll demonstrate how to flashback a…