Re: Commitment Control Overhead

["Al Barsa, Jr." <barsa2@xxxxxxx>]

At 04:56 PM 3/9/98 -0600, you wrote:
>Can someone steer me in the direction of statistics about using Commitment
Control.  I have only found the Advanced Backup and Recovery text talking
about CC, so far.
>
>It looks like there will be at least two added disk I-Os for journaling
the before and after images of each record; two added disk I-Os for
journaling the start and end commitment boundary for each logical unit of
work (LUW).  If I use OMTJRNE on my journal definition, I may avoid the
writing of journal entries for the history of LUW resources and save on
those I-Os.
>
>So, for example, if I have two write statements in my LUW, I increase the
disk I-Os by 4 + 2, or 3 times as many disk I-Os as without CC.
>
First of all, commitment control requires journaling.  The overhead of
journaling is about 5%, assuming the journal receiver is in a separate ASP
that has not overflowed.  The new 'remote journaling' support in V4R2 is
about 14%.

Commitment control itself (after you get over the additional hurdle of
writing and testing the programs) is relatively cheap, assuming that you
COMMIT to the database.  In the event that you perform a ROLLBACK (in your
own code, or uncommitted transactions are implicitly rolled back at IPL
time), commitment control is very expensive.

The design of commitment control assumes that you will ultimately COMMIT
the transactions.  I suspect that there is one additional I-O to the
journal indicating that the COMMIT occurred.

Al




Al Barsa, Jr. - Account for Midrange-L
Barsa Consulting, LLC.  
400 > 390

Phone:  914-251-9400
Fax:    914-251-9406





Private mail should be sent to barsa@ibm.net
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