Oracle DBA Troubleshooting Interview Questions - 2

Question: 6

What is the ORA-01555: snapshot too old error? How can it be avoided?

The ORA-01555: snapshot too old error indicates that the query cannot find the snapshot it is looking for in the rollback segment.

Rollback segment is designed to hold data blocks that are being changed. It is required to hold old snapshot until the transaction is committed. However, it holds the data until the space is required for other transactions.

Question: 7

How do you handle ORA – 01403: no data found error?

You can handle ORA- 01403: no data found error by terminating the processing for the SELECT statement.

Question: 8

Explain wait events?

Wait event occurs when a user process is kept waiting because of some problem, such as an I/O bottleneck or a busy CPU.

The information about wait event is available in the V$SYSTEM_WAIT and V$SESSION_WAIT dynamic performance views.

Question: 9

What is db file sequential read wait event?

The db file sequential read wait event performs single block read operations against indexes, tables, control files, rollback segments and data file headers.

It has three parameters: file#, firstblock# and block count.

Question: 10

What is cost based optimizer?

Cost based optimizer is the optimizer component of the Oracle, which is recommended and supported by Oracle.

It determines query plans based on overall cost of usage of each resource to get the best possible plan with respect to the resource usage cost.

It uses internal statistics to determine the best execution plan for the statement.