> -----Original Message-----
> From: IBM Mainframe Discussion List [mailto:IBM-MAIN@LISTSERV.UA.EDU] On
> Behalf Of Tom Marchant
> Sent: 12 April, 2017 15:03
> To: IBM-MAIN@LISTSERV.UA.EDU
> 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.

> That makes no sense to me.

This does?

Kees.
> 
> --
> Tom Marchant


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