Re: Keeping clean pages in shared memory

At 11:13 AM 3/2/95 GMT, Andy Kent wrote: }> > 1) If a buffer is written to, say, every 30 seconds and you flush it }> > once a minute, you'll do five times as many disk writes for it than }> > with a 5-minute checkpoint }> }> That's what we thought but it wasn't the case. We basically came to }the }> conclusion that the page cleaning activity was done when the disk was }> not busy. }....... }> Big checkpoint are noticeable by the user which is why we steer clear }of }> them. } } }But what if the system *is* disk-bound during page cleaning? I don't }think Online takes into account other disk activity when deciding whether }to flush - it's all based on snooze times and LRU thresholds. If, as on }two installations I've seen in the last few weeks, you've got a }write-hammered application doing unbuffered log writes to a disk which }also happens to contain data, the last thing you want is the page }cleaners to kick in. In a more balanced application where consistent }response times are the main objective, then yes I can see that the goal }would be to keep checkpoints short. } All the more reason to keep logs in their own partition/disk whenever possible, and seperate from the physical log and rootdbs. Jon }> > - I can't recall whether fuzzy flushes do sorted writes. I seem to }> > remember reading one manual or document that said they do, another }> > that said they don't. }> }> I can't work out how it knows since it does the least recently used }page }> first. } }No, I think you miss my point. Writes are sorted into physical order at }checkpoint time. My question was, is the same thing done for a fuzzy }flush, also how do these sorts work? } } }akent@cix.compulink.co.uk (Andy Kent) }------------------------------------------------ }Freelance Informix Database Specialist, }Redland, Bristol, England } } ================================================================== Jon Vemo Internet: jvemo@cyberspace.com Bothell, WA USA ------------------------------------------------------------------ Watch out for road-kill on the information superhighway....SPLAT!! ==================================================================