system page size!

I am confused with the system page size, now? Where can I see what system page size informix is using? The last line of onstat -b tells me 2048 buffer size.... but on HP-UX dmesg shows this: physical page size = 4096 bytes, logical page size = 4096 bytes Is this physical page size something else? Sent via Deja.com http://www.deja.com/

Sorry but I think you've answered your own question ... surely your System is a HP and that says it's page size is 4096 so your system page size is 4096 Yours -- Earle A Long (Senior Informix DBA) SINGLEPOINT UK LTD "Murat YILDIZ" <murat-y@usa.net> wrote in message news:93jktn$dcp$1@nnrp1.deja.com... > I am confused with the system page size, now? > Where can I see what system page size informix is using? > > The last line of onstat -b tells me 2048 buffer size.... > but on HP-UX dmesg shows this: > physical page size = 4096 bytes, logical page size = 4096 bytes > > Is this physical page size something else? > > > Sent via Deja.com > http://www.deja.com/ >

Murat YILDIZ wrote: > I am confused with the system page size, now? > Where can I see what system page size informix is using? > > The last line of onstat -b tells me 2048 buffer size.... > but on HP-UX dmesg shows this: > physical page size = 4096 bytes, logical page size = 4096 bytes > > Is this physical page size something else? There are multiple pages sizes available to confuse the unwary (or the inquisitive). Informix is using logical pages of 2 KB (onstat -b), which is the normal Informix page size on most systems. At the time when it was instituted (1988?), most operating systems were using a 1 KB or 2 KB page size, so Informix's page size was a multiple of the system page size, which was good. Over time, the operating systems increased their page size from 1 or 2 to 4 KB, but Informix was unable to change its page size to match for a variety of reasons. These include the problems of forwards and backwards migration -- rewriting an entire database is a slow process -- and the fact that it is easier to waste space with internal fragmentation on a 4 KB page. By that, I mean that if you have a a row size smaller than ((4096 - 28) / 255 - 4) or 11 bytes (eg a cross-reference table with 2 INTEGER values, each referencing rows in another table), then you are stuck with just 255 rows per page, even though if you were not limited by the slot numbering, you could fit in more than 255 rows. So, I don't know of any platform where there was initially a 2 KB page version of OnLine which subsequently changed to a 4 KB page size. I believe XPS 8.3x does provide variable size pages. What does the page size mismatch mean? Probably not very much. ...I don't like the conclusion I'm coming to, so I'm not sure whether I'm right... In the worst case (a cooked file), when OnLine reads a 2 KB page, the o/s reads 4 KB from disk and transfers 2 KB of that to Informix's shared memory cache. If it needs the next 2 KB before it removes the (o/s) page from the (o/s) cache, then no further disk read is needed. If the user writes to the page after the o/s clears the page from its cache, then it has to reread the 4 KB page, modify the 2 KB from the Informix cache, and then write back the 4 KB page. Similar rules might apply to raw disk devices too; the o/s will read 4 KB, return the relevant 2 KB to Informix, and discard (actually discard) the other 2 KB. Hmmmm, I wonder how much of a performance boost would be available if we resized the Informix pages to match (or exceed) the o/s page size. If I were redesigning the Informix page layouts, I'd use big pages (like 64 KB) with 8 byte rowids and 16-bit slot numbers. For the immediately foreseeable future, that would be bigger than the o/s page size, and therefore would not require the discarding of pages. And, going back to the original question, the fact that the o/s uses one page size and Informix uses another does not cause confusion to either piece of software because they are referring to different sorts of pages (though it may cause some extra work for the o/s). -- Yours, Jonathan Leffler (Jonathan.Leffler@Informix.com) #include <disclaimer.h> Guardian of DBD::Informix v1.00.PC1 -- http://www.perl.com/CPAN "I don't suffer from insanity; I enjoy every minute of it!"