In <EB45A9EC1D5DD111BB1C0001FA68961980C2FD@exch5>, on 05/27/98
   at 06:26 AM, "Sanders, David" <DSanders AT INTERNAL.MASSMUTUAL DOT COM> said:

>Since I tend to be against mirroring, this could change my mind if what
>Jason says is true!

>There are 2 questions that I have:
>1) Does the recovery log get written to after every activity, or does it
>buffer activity for awhile before writing?
>        *if every activity immediately writes to the primary log and then
>to the mirrored-log, then I guess I'd have to rethink the mirroring thing
>        *if every activity DOESN't get written to the primary log
>immediately, then mirroring accomplishes nothing since the content of the
>buffer is broken and either neither log gets written to, or both get
>written to badly.
>2) If you have a busy system and a -write to a mirrored log- has to wait
>for a write to finish on the primary log, does this negatively affect
>performance?
>        *I guess this would have to be accepted as a cost for having the
>redundancy
>        *Or, it's not detectable

I don't have any definitive answers, but I do have important
empirical information about this.  This thread was discussed
a few months ago and I decided then to turn on mirrorwrite
sequential for the log (I don't mirror the db).  There was no
performance impact at all.  I measured the performance by
comparing the speed of the expire inventory process.

My server is on OS/390, adsm level is 2.1.13.

(I suspect that writes to the log are not after every
activity but only after each database commit).

>Dave Sanders
>Sr. Technical Consultant
>DSanders AT massmutual DOT com
>1295 State St, E060, Springfield, MA 01111
>413-744-5095
>!@#$%

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Bill Colwell
Bill Colwell
C. S. Draper Lab
Cambridge, Ma.
bcolwell AT draper DOT com
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