Re: request for enhancement: 2K -> 4K

This is a multi-part message in MIME format. --------------9187A4A65CC2C1E8EF5567AF Content-Type: text/plain; charset=us-ascii Content-Transfer-Encoding: 7bit Jon Vemo wrote: > > At 11:49 AM 12/15/97 +0000, you wrote: > }David Williams wrote: > } > }> In article <3494a300.1118117@news.xs4all.nl>, Reinoud van Leeuwen > }> <reinoud@xs4all.nl> writes > }> >On 12 Dec 1997 09:26:16 -0700, Pablo Sanchez <pablo@sgi.com> wrote: > }> > > }> >>Sybase Inc., > }> >> > }> >>I'd like to request that we increase the atomic page size > }> >>from 2K to 4K. Today's systems I/O subsystems can handle > }> >>the larger page sizes. It'd be nice to have pages greater > }> >>than 2K for DSS type of applications. OLTP, I don't > }> >>believe, would suffer. (Informix uses a 4K page size and > }> >>they do pretty well...) with DSS app's, one has > }> >>denormalization that tends to create fat rows... how about > }> >>it? > }> > > }> >The disadvantage is that 4 K will be the minumum size for all > }> >allocations, resulting in more wasted space in the database... > }> >_______________________________________ > }> > }> With 2Gb (2048Mb) even wasting 20Mb is only 1%! Surely you don't > }> size things that 1% more will mean you need to buy another disk? > }> > }> I come from tge Informix side and I'd like things similar to > }> Informix's blobspaces. You have normal database spaces which have > }> 2K or 4K pages depending upon the specific port. within blobspaces > }> you then define how large a blobpage will be in units of either > }> 2K or 4K. Big buffers (up to, I think 32K) are using to access > }> blobspaces. > }> > }> Why can't we just define our own page sizes for each area of disk > }> we use? Say in units of 2K or 4K depending upon the machine type? > }> > }> -- > }> David Williams > } > }The paging functions in the Informix engine were complicated enough to > }understand in v5.01 with only 2K pages, and I am unaware of how much it has > }increased in the later versions, ie. 6+. I would think that this would not > }be approved on the same grounds as you described above. Developing and > }looking after this would simply be ugh! > > As I understand it, even in pre-6.x, the page size for Informix was platform > specific. Most ports were done with a 2K page, however some which showed > performance advantages with a larger page size, were ported as 4K. Sequent > is one example. > > Jon We are currently facing severe I/O performance problems on several of our HP9000 K2x0 SMP machines running HP-UX 10.10 and Informix Online 7.20. All these machines have a Nike HA disk array configured in RAID0/1 or RAID1. This is clearly demonstrated by the long checkpoints during operations (10-20sec). The problem is that the Unix SCSI driver has an overhead of +/- 1ms per I/O operation. When a checkpoint needs to write dirty buffers to disk containing 20MB of dirty data, and when you write with a page size of 2k to raw devices, you have a total overhead of 10sec!! This has been verified with following command: time dd if=/dev/mem of=/dev/vginformix/rlvtest bs=2k count=10000 Real: 18,8sec An increased page size decreases the needed time dramatically. A configurable page size would definately help. We don't mind weasting some more disk space as a result of this. --------------9187A4A65CC2C1E8EF5567AF Content-Type: text/x-vcard; charset=us-ascii; name="vcard.vcf" Content-Transfer-Encoding: 7bit Content-Description: Card for De Smedt, Walter Content-Disposition: attachment; filename="vcard.vcf" begin: vcard fn: Walter De Smedt n: De Smedt;Walter org: DHL International adr: ;;Woluwelaan 151;Diegem;;1831;Belgium email;internet: wdesmedt@bru-co.be.dhl.com title: System Administrator (COE) tel;work: +32 2 719 67 74 tel;fax: +32 2 720 07 79 x-mozilla-cpt: ;0 x-mozilla-html: FALSE version: 2.1 end: vcard --------------9187A4A65CC2C1E8EF5567AF--