Interview ques

1.What Is Performance Tuning?

Making optimal use of system using existing resources called performance tuning.

2. What Are The Types Of Tunings?

The types of tuning are:

• CPU Tuning

• Memory Tuning

• IO Tuning

• Application Tuning

• Database Tuning

3.What Mainly Database Tuning Contains?

• RBO (Rule Based Optimizer)

• CBO (Cost Based Optimizer)

4.What Are The Pre Requsited To Make Use Of Optimizer?

• Set the optimizer mode

• Collect the statistics of an object

5.How Do You Collect Statistics Of A Table?

Analyze table emp compute statistics or analyze table emp estimate statistics.

6.How Do You Delete Statistics Of An Object?

Analyze table emp delete statistics.

7.How Many Types Of Hits Are There And What Are They?

There are two types of hits, they are

• Buffer hit

• library hit

8.What Are The Types Of Wait Events?

• cpu time

• direct path read

9.How Do You Set Up Tablespaces During An Oracle Installation?

You should always attempt to use the Oracle Flexible Architecture standard or another partitioning scheme to ensure proper separation of SYSTEM, ROLLBACK, REDO LOG, DATA, TEMPORARY and INDEX segments.

10.What Are Some Indications That You Need To Increase The Shared_pool_size Parameter?

Poor data dictionary or library cache hit ratios, getting error ORA-04031. Another indication is steadily decreasing performance with all other tuning parameters the same.

11.What Is The General Guideline For Sizing Db_block_size And Db_multi_block_read For An Application That Does Many Full Table Scans?

Oracle almost always reads in 64k chunks. The two should have a product equal to 64 or a multiple of 64.

12.What Is The Fastest Query Method For A Table?

Fetch by rowid is the fastest query method for a table.

13.Explain The Use Of Tkprof? What Initialization Parameter Should Be Turned On To Get Full Tkprof Output?

The tkprof tool is a tuning tool used to determine cpu and execution times for SQL statements. You use it by first setting timed_statistics to true in the initialization file and then turning on tracing for either the entire database via the sql_trace parameter or for the session using the ALTER SESSION command. Once the trace file is generated you run the tkprof tool against the trace file and then look at the output from the tkprof tool. This can also be used to generate explain plan output.

14.When Should You Increase Copy Latches? What Parameters Control Copy Latches?

When you get excessive contention for the copy latches as shown by the “redo copy” latch hit ratio. You can increase copy latches via the initialization parameter LOG_SIMULTANEOUS_COPIES to twice the number of CPUs on your system.

15.Where Can You Get A List Of All Initialization Parameters For Your Instance? How About An Indication If They Are Default Settings Or Have Been Changed?

You can look in the init.ora file for an indication of manually set parameters. For all parameters, their value and whether or not the current value is the default value, look in the v$parameter view.

16.Discuss Row Chaining, How Does It Happen? How Can You Reduce It? How Do You Correct It?

Row chaining occurs when a VARCHAR2 value is updated and the length of the new value is longer than the old value and won’t fit in the remaining block space. This results in the row chaining to another block. It can be reduced by setting the storage parameters on the table to appropriate values. It can be corrected by export and import of the effected table.

17.When Looking At The Estate Events Report You See That You Are Getting Busy Buffer Waits. Is This Bad? How Can You Find What Is Causing It?

Buffer busy waits may indicate contention in redo, rollback or data blocks. You need to check the v$waitstat view to see what areas are causing the problem. The value of the “count” column tells where the problem is, the “class” column tells you with what. UNDO is rollback segments, DATA is data base buffers.

18.What Can Cause A High Value For Recursive Calls? How Can This Be Fixed?

A high value for recursive calls is cause by improper cursor usage, excessive dynamic space management actions, and or excessive statement re-parses. You need to determine the cause and correct it By either relinking applications to hold cursors, use proper space management techniques (proper storage and sizing) or ensure repeat queries are placed in packages for proper reuse.

19.If You See A Pin Hit Ratio Of Less Than 0.8 In The Estate Library Cache Report Is This A Problem? If So, How Do You Fix It?

This indicates that the shared pool may be too small. Increase the shared pool size.

20.If You See The Value For Reloads Is High In The Estate Library Cache Report Is This A Matter For Concern?

Yes, you should strive for zero reloads if possible. If you see excessive reloads then increase the size of the shared pool.