Tuesday, August 12, 2008

TKPROF--Performance Tunning -2

Hi All,
Now we will see how to read the trace files..It is very difficult to understand from the trace files so we use the TKPROF utility to make the trace files in a better readable format..
This is one of the documents i had which i collected from metalink..a good one with clear examples...
If you have a system that is performing badly, a good way to identify problem SQL statements is to trace a typical user session and then use TkProfto format the output using the sort functions on the tkprof command line.
There are a huge number of sort options that can be accessed by simply typing 'TkProf' at the command prompt.
A useful starting point is the 'fchela' sort option which orders the output by elapsed time fetching (rememberthat timing information is only available with timed_statistics set to true in the "init.ora" file).
The resultant .prf file will contain the most time consuming SQL statement at the start of the file.

Another useful parameter is sys.
This can be used to prevent SQL statements run as user SYS from being displayed. This can make the output file much shorter an easier to manage.
Remember to always set the TIMED_STATISTICS parameter to TRUE when tracingsessions as otherwise no time based comparisons can be made.
A typical TKPROF out look like for select,insert,update,delete..
call count cpu elapsed disk query current rows
--------- ------------------------------------------------------------------------------------
Parse 2 221 329 0 45 0 0
Execute 3 9 17 0 0 0 0
Fetch 3 6 8 0 4 0 1
------------------------------------------------------------------------------- --------------
Let see the definition for each and every column
Interpreting TkProf Output Guidelines
call : Statisics for each cursor's activity are divided in to 3 areas:
Parse: statisitics from parsing the cursor.
This includes information for plan generation etc.
Execute: statisitics for the exection phase of a cursor
Fetch : statistics for actually fetching the rows

count : number of times we have performed a particular activity on this particular cursor
cpu: cpu time used by this cursor
elapsed: elapsed time for this cursor
disk: This indicates the number of blocks read from disk.
Generally you want to see blocks being read from the buffer cache rather than disk.
query : This column is incremented if a buffer is read in Consistent mode.
A Consistent mode buffer is one that has been generated to give a consistent read snapshot for a long running transaction.
The buffer actually contains this status in its header.
current: This column is incremented if a buffer found in the buffer cache that is new enough for the current transaction and is in current mode (and it is not a CR buffer).
This applies to buffers that have been read in to the cache as well as buffers that already exist in the cache in current mode.
rows: Rows retrieved by this step
What is my first step while tunning the performance of a query ?
It is better to use autotrace feature of SQL*Plus be used on statements rather than using TkProf mainly because the TkProf output can be confusing with regard to whether the Rule or Cost Based optimizer has been used. Because TkProf explain plan does not show any costs or statistics,
it is sometimes not possible to tell definitively which optimizer has been used.
That said, the following output from Tkprof explain plan is useful.
The Rows column next to the explain plan output shows the number of rows processed by that particular step.
The information is gathered from the STAT lines for each cursor in the raw trace output.
Remember that if the cursor is not closed then you will not see any output.
Setting SQL_TRACE to false DOES NOT close PL/SQL child cursors.
Cursors are closed in SQL*Plus immediately after execution.
Let's see some tkprof examples ..in the next post..

7 comments:

kodangal gouthami said...

Hi Murthy,

Can u give some real time examples on customisations of AP,AR,GL MOdules.And also explain what are Folder options.How these are used in customisations.

Thanks

Goutami

John said...

Hi Murthy,
I agree that using the trace is a big pain. Your info on the TKPROF utility is great, and using the 'fchela' sort option will help us get the perf problem nailed quickly now. Thanks for the post.
J Gooding.
Mortgage
broker in Brisbane

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