On Wed, 12 Apr 2017 13:08:32 +0000, Vernooij, Kees wrote: >
>> -----Original Message----- >> From: IBM Mainframe Discussion List [mailto:[email protected]] On >> Behalf Of Tom Marchant >> Sent: 12 April, 2017 15:03 >> To: [email protected] >> Subject: Re: Paging subsystems in the era of bigass memory >> >> On Wed, 12 Apr 2017 06:28:05 +0000, Vernooij, Kees wrote: >> >> >From here, there the story still goes on IIRC: if DB2 again needs >> >the data, it would be paged in in any normal task. However, DB2 >> >is more intelligent: it keeps track of how long it takes to page-in >> >the page or read it again from disk, in a I/O that is already running. >> >If the latter is faster this is used and the aux slot is really >> useless. >> >> Are you suggesting that before DB2 references a page containing a >> buffer, it checks to see if it is paged out? > >Yes. > >> And that if it is paged >> out, >> it doesn't use the record in the buffer, but instead reads it into a >> different page? > >No, it checks its(?) statistics about page-in time and reading it directly >from dasd and then decides which will be faster. I heard this years ago, >when heavy paging systems might produce slow page-ins and adding a >page to an in-progress pre-fetch could be faster. So, if it thinks it would be faster to read the record from DASD than for MVS to page in the buffer page(s) containing the record, it will read the record into different pages that have not been paged out? It still makes no sense to me. It certainly can't read the record into the same page, because that would require that the page be paged in first. And what does it do with the old buffer page? Stop using it? Freemain and getmain again so that the page slot becomes superfluous? > >> That makes no sense to me. > >This does? What? -- Tom Marchant ---------------------------------------------------------------------- For IBM-MAIN subscribe / signoff / archive access instructions, send email to [email protected] with the message: INFO IBM-MAIN
