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Shadow copy/merge in 7.3-2

Torfi Olafur Sverrisson_1
Occasional Advisor

Shadow copy/merge in 7.3-2

Hi

In OpenVMS 7.3-2 the use of spinlock has been reduced alot. Is there any knowledge of how much this has increased performance of shadow merge or shadow copy?

Regards, Torfi.
4 REPLIES
Ian Miller.
Honored Contributor

Re: Shadow copy/merge in 7.3-2

I don't know if your question is answerable as shadow merge/copy performance depends on your systems and how they are connected. How much improvement you see depends on what you are upgrading from.
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Purely Personal Opinion
John Gillings
Honored Contributor

Re: Shadow copy/merge in 7.3-2

Torfi,

Reduction in spinlock contention will only improve performance if it was a bottleneck. If your systems were running with high MPSYNCH (say, > 60%) during merge or copy operations, then you *may* experience an improvement.

Otherwise, you need to identify the most significant bottle neck and address it. A few simple things, try and have the TARGET disk local to the system performing the merge or copy. Try to avoid accessing a shadowset undergoing a merge.
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Torfi Olafur Sverrisson_1
Occasional Advisor

Re: Shadow copy/merge in 7.3-2

Thank you for your relies.



We are running Oracle RDBMS on shadow sets on EMA12000 boxes. What we have experienced is that in the case of disturbance of the shadow set, forcing merge to take place, we have had to break the 2 member shadow and perform a full copy at a later hour when traffic has decreased. A understand that a mini-copy should be the fastest algorithm for shadow sets recovery as it uses only 4 I/Os instead of 5 in full copy. But I have not seen how one can invoke a mini-copy instead of full. Any comments on that?


Regards, Torfi.

Ian Miller.
Honored Contributor

Re: Shadow copy/merge in 7.3-2

when a member disk is dismounted you can specify /POLICY=MINICOPY=OPTIONAL on the dismount command to ensure writes are tracked with a bitmap hence allowing min-copy to be used. minimerge requires hardware assistance (disks on HSJ or HSC controllers).
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