Oracle Performance Tuning Interview Questions And Answers

Oracle Performance Tuning Interview Questions And Answers. If you are looking for Performance Tuning Interview Questions, here is the comprehensive list from basic to most advanced oracle database performance tuning interview questions for 2+, 3+, 4+, 5+ years of experienced professionals. These oracle performance tuning interview questions will help you to crack your oracle job interview.

Oracle Performance Tuning Interview Questions

What Is Performance Tuning?

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

What Are The Types Of Tunings?

CPU TuningMemory TuningIO TuningApplication TuningDatabase Tuning

What Mainly Database Tuning Contains?

Hit RatiosWait Events

What Is An Optimizer?

Optimizer is a mechanism which will make the execution plan of an sql statement.

What Are The Types Of Optimizers?

RBO(Rule Based Optimizer)CBO(Cost Based Optimizer)

Which Optimizer Is The Best One?

CBO

What Are The Pre Requsited To Make Use Of Optimizer?

Set the optimizer modeCollect the statistics of an object

How Do You Collect Statistics Of A Table?

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

What Is The Diff Between Compute And Estimate?

If you use compute, The FTS will happen, if you use estimate just 10% of the table will be read

Data Dictionary Follows Which Optimizer Mode?

RBO.

How Do You Delete Statistics Of An Object?

Analyze table emp delete statistics.

How Do You Collect Statistics Of A User/schema?

exec dbms_stats.gather_schema_stats(scott)

How Do You See The Statistics Of A Table?

select num_rows,blocks,empty_blocks from dba_tables where tab_name=’emp’

What Are Chained Rows?

These are rows, it spans in multiple blocks.

Oracle Performance Tuning Interview Questions And Answers

How Do You Collect Statistics Of A User In Oracle Apps?

fnd_stats package.

How Do You Know What Sql Is Currently Being Used By The Session?

By goind v$sql and v$sql_area.

What Is A Execution Plan?

Its a road map how sql is being executed by oracle db..

How Do You Get The Index Of A Table And On Which Column The Index Is?

dba_indexes and dba_ind_columns

Which Init Parameter You Have To Set To Bypass Parsing?

cursor_sharing=force

How Do You Know Which Session Is Running Long Jobs?

by going v$session_longops

How Do You Flush The Shared Pool?

alter system flush shared_pool

How Do You Get The Info About Fts?

using v$sysstat

How Do You Increase The Db Cache?

alter table emp cache

Where Do You Get The Info Of Library Cache?

v$librarycache

How Do You Get The Information Of Specific Session?

v$mystat

How Do You See The Trace Files?

using tkprof usage: tkprof allllle.trc llkld.txt

Performance Tuning Interview Questions

A tablespace has a table with 30 extents in it. Is this bad? Why or why not?

Expected answer: Multiple extents in and of themselves aren’t bad.

However, if you also have chained rows this can hurt performance.

How do you set up tablespaces during an Oracle installation?

Expected answer: 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.

You see multiple fragments in the SYSTEM tablespace, what should you check first?

Expected answer: Ensure that users don’t have the SYSTEM tablespace as their TEMPORARY or DEFAULT tablespace assignment by checking the DBA_USERS view.

What are some indications that you need to increase the SHARED_POOL_SIZE parameter?

Expected answer: 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.

What is the general guideline for sizing db_block_size and db_multi_block_read for an application that does many full table scans?

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

What is the fastest query method for a table?

Expected answer: Fetch by

rowid

Explain the use of TKPROF? What initialization parameter should be turned on to get full TKPROF output?

Expected answer:

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.

When looking at v$sysstat you see that sorts (disk) is high. Is this bad or good? If bad, how do you correct it?

Expected answer: If you get excessive disk sorts this is bad. This indicates you need to tune the sort area parameters in the initialization files. The major sort are parameter is the SORT_AREA_SIZe parameter.

Advanced Oracle Performance Tuning Interview Questions

When should you increase copy latches? What parameters control copy latches?

Expected answer: 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.

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?

Expected answer: 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.

Describe hit ratio as it pertains to the database buffers. What is the difference between instantaneous and cumulative hit ratio; which should be used for tuning?

Expected answer: Hit ratio is a measure of how many times the database was able to read a value from the buffers verses how many times it had to re-read a data value from the disks.

A value greater than 80-90% is good, less could indicate problems. If you take the ratio of existing parameters this will be a cumulative value since the database started.

If you do a comparison between pairs of readings based on some arbitrary time span, this is the instantaneous ratio for that time span. Generally speaking an instantaneous reading gives more valuable data since it will tell you what your instance is doing for the time it was generated over.

Discuss row chaining, how does it happen? How can you reduce it? How do you correct it?

Expected answer: 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.

Oracle Database Tuning Questions

When looking at the estat events report you see that you are getting busy buffer waits. Is this bad? How can you find what is causing it?

Expected answer: 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.

If you see contention for library caches how can you fix it?

Expected answer: Increase the size of the shared pool.

If you see statistics that deal with “undo” what are they really talking about?

Expected answer: Rollback segments and associated structures.

If a tablespace has a default pctincrease of zero what will this cause (in relationship to the smon process)?

Expected answer: The SMON process won’t automatically coalesce its free space fragments.

If a tablespace shows excessive fragmentation what are some methods to defragment the tablespace? (7.1,7.2 and 7.3 only)

Expected answer: In Oracle 7.0 to 7.2 The use of the ‘alter session set events ‘immediate trace name coalesce level ts#’;’ command is the easiest way to defragment contiguous free space fragmentation.

The ts# parameter corresponds to the ts# value found in the ts$ SYS table. In version 7.3 the ‘alter tablespace coalesce;’ is best. If free space isn’t contiguous then export, drop and import of the tablespace contents may be the only way to reclaim non-contiguous free space.

How can you tell if a tablespace has excessive fragmentation?

If a select against the dba_free_space table shows that the count of a tablespaces extents is greater than the count of its data files, then it is fragmented.

You see the following on a status report:
redo log space requests 23
redo log space wait time 0
Is this something to worry about? What if redo log space wait time is high? How can you fix this?

Expected answer: Since wait time is zero, no. If wait time was high it might indicate a need for more or larger redo logs.

References:

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