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  Oracle Tips by Burleson

Results of taking a STATSPACK snapshot Frequency

After taking the initial snapshot, allow a short period time to pass and then repeat the process.  As soon as there are at least two snapshots with no database downtime in between, prepare a report on the database activity during that interval.  The length of the time interval is the subject of a great deal of debate among DBAs.  Ideally, the interval should be just long enough so that the problem-related statistics will be completely collected, but short enough to omit other statistics which might obscure the relevant data.  The goal is to avoid a condition in which the spike in the statistics that indicate the problem gets ‘averaged-out’ of the picture.

If STATSPACK is run via a cron job or from a job scheduling package, it can easily be scheduled to run at a frequency ranging from once every minute to once a month or anywhere in between.  The trick is to find the balance between too often and not often enough.  For most reactive tuning situations, snapshots taken at intervals from five to fifteen minutes apart will provide a reasonable amount of data to make a good start on tuning. 

An important thing to remember is that even if statistics are gathered too frequently with STATSPACK, reporting can always be done on a larger time window.  For example, if snapshots are at five-minute intervals and there is a report that takes 30 minutes to run, that report may or may not be slow during any given five-minute period.  After looking at the five-minute windows, the DBA can decide to look at a 30-minute window and then run a report that spans six individual five-minute windows.  The moral of the story is to err on the side of sampling too often rather than not often enough.


The above book excerpt is from:

Oracle Wait Event Tuning

High Performance with Wait Event Interface Analysis 

ISBN 0-9745993-7-9  

Stephen Andert 

http://www.rampant-books.com/book_2004_2_wait_tuning.htm

  
 

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