Beginning Oracle Database 11g Administration From Novice to Professional

CHAPTER 11 FIXING PROBLEMS 245
In the preceding example, two users are modifying the same data. Deadlock also
occurs in the next example, even though the users are modifying different data. At step
3, user A will be blocked because Oracle needs to verify the absence of child records
before deleting a parent record. In the absence of an index on the column of the
table, Oracle attempts to lock the entire table and is prevented from doing so
because user A has a lock on one of the records in the table. User B is blocked in turn at
step 4, and a deadlock results:
Defects in database design such as un- indexed foreign keys can increase the frequency
of deadlocks, but deadlocks can happen any time more than one user is using the database.
All database programs must anticipate the possibility and take the appropriate action
when a deadlock happens—that is, issue the command and retry the transaction.
ORA-00600: Internal Error Code
Oracle reports an ORA- 00600 error in the alert log whenever it encounters an unexpected
condition—the frequent cause is an Oracle bug—and stops processing the SQL statement
it was processing at the time. Here is the verbiage from Oracle Database 11g Error
Messages:
Caution ORA-00600 errors should always be investigated, and the DBA should confirm that the error
was not triggered by a corrupted data block.