The number and size of paging volumes set an upper limit to the amount of
virtual storage that can be in use at any one time across all address spaces.
This alone does not impact paging rates. Only the amount of real storage
affects paging rates. (Note: this may not be 100% technically true, but it is
close enough for this context.)
A demand page in event can cause a full stop in the requesting address space as
a main storage frame is made available (perhaps driving a page out to DASD
operation) and the desired page is fetched from DASD. Even with very fast DASD
with 100% cache hit rates, this is pretty slow.
The amount of real memory determines how often a demand paging operation
occurs. Ideally, that should average zero. As a practical matter, an overall
system demand page rate of one or two pages per second can mean that you have a
good balance between main storage and workload demand, but there isn't much
room to grow.
In my mind, 'acceptable paging' is when service levels are being met. Usually
that means that there is little or no time spent waiting on demand paging
operations. Unacceptable paging is when service levels are not being met AND
the cause is diagnosed as waiting on page fault resolution.
OBTW - I've found the following terms to be useful:
> A 'page' is 4096 bytes of virtual storage.
> A 'frame' is 4096 bytes of main storage.
> A 'slot' is 4096 bytes of DASD storage.
A page always consumes a slot, but consumes a frame only when 'in'.
HTH and good luck.
-----Original Message-----
From: IBM Mainframe Discussion List [mailto:[email protected]] On Behalf Of
Lopez, Sharon
Sent: Wednesday, February 08, 2012 8:26 AM
To: [email protected]
Subject: Re: Acceptable paging
We have a z/10 and this test lpar had 11G of real memory. IBM is loaning us
16G of real memory so now we have 27G of real memory. We had 3 mod-9 page
datasets and after message broker started we had to add 4 additional mod-9 page
datasets. We do have IMS, CICS, and DB2 running on this system. Our tuning
guy retired last year and none of us left understand how this is supposed to
work. Thanks.
-----Original Message-----
From: IBM Mainframe Discussion List [mailto:[email protected]] On Behalf Of
Lizette Koehler
Sent: Wednesday, February 08, 2012 9:11 AM
To: [email protected]
Subject: Re: Acceptable paging
>
> Can someone please help me determine what the 'acceptable paging'
> should
be on a
> system? We are having issues with MQ and broker. Thanks.
>
Could you describe your environment a little?
CPU(s) (z10, z9 , etc)
Amount of dasd space allocated to Page Datasets? Number of Page Datasets Real
Memory available Number of MQ and Brokers?
Connection types (IMS, CICS, Distributed systems)
Many elements can play into tuning a system. This will help in answering the
question.
Now, when you ask about acceptable paging in relationship to MQ, is anything
else in play? CICS, IMS, DB2, heavy batch, etc. or is MQ the only thing
running on that system?
Or perhaps I misunderstood your acceptable paging in relationship to MQ.
Thanks
Lizette
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