Re: Keeping clean pages in shared memory

> > 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. > > - 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