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:IBM-MAIN@bama.ua.edu] On Behalf Of Lopez, Sharon Sent: Wednesday, February 08, 2012 8:26 AM To: IBM-MAIN@bama.ua.edu 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:IBM-MAIN@bama.ua.edu] On Behalf Of Lizette Koehler Sent: Wednesday, February 08, 2012 9:11 AM To: IBM-MAIN@bama.ua.edu 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 ---------------------------------------------------------------------- For IBM-MAIN subscribe / signoff / archive access instructions, send email to lists...@bama.ua.edu with the message: INFO IBM-MAIN ________________________________ E-mail correspondence to and from this address may be subject to the North Carolina Public Records Law and may be disclosed to third parties by an authorized state official. ---------------------------------------------------------------------- For IBM-MAIN subscribe / signoff / archive access instructions, send email to lists...@bama.ua.edu with the message: INFO IBM-MAIN NOTICE: This electronic mail message and any files transmitted with it are intended exclusively for the individual or entity to which it is addressed. The message, together with any attachment, may contain confidential and/or privileged information. Any unauthorized review, use, printing, saving, copying, disclosure or distribution is strictly prohibited. If you have received this message in error, please immediately advise the sender by reply email and delete all copies. ---------------------------------------------------------------------- For IBM-MAIN subscribe / signoff / archive access instructions, send email to lists...@bama.ua.edu with the message: INFO IBM-MAIN