Re: Logical log write volumes

Andy Kent (akent@cix.compulink.co.uk) wrote: : > The calculation should be something like: : > : > 16 bytes + rowsize for each row inserted : > 16 bytes + indexsize for each row/for each index on the table : > (these numbers might be +/-4 in either direction) : > : > This is for an insert. Updates and deletes are different. : If the minimum unit of work is a page, won't it be one page per insert : with unbuffered? No! Your transaction will only initiate one page (or more) written when it COMMITs, not one per insert. The page wastage will depend on factors like how many rows you alter per transaction, how many other transactions commit during your transaction and how fast they do it (ie how often Group Commit kicks in). And if you do ten inserts to the same page, won't that : mean only one *disk* i/o with buffered (as long as all ten inserts are : between buffer flushes)? Yes. But you're talking about the (async) buffer i/o not the log i/o. I don't see what that has to do with log i/o. You will get ~1 log i/o per transaction with Unbuffered Logging (unless throughput is sufficiently high that Group Commit is the norm). You will get <<1 log i/o per transaction with Buffered Logging (assuming average log data per transaction < Logical Log Buffer size). Obviously (I hope), if your average log data per transaction is > Logical Log Buffer size then you will get >1 log i/o per transaction with either Unbuffered or Buffered Logging. : akent@cix.compulink.co.uk (Andy Kent) : ------------------------------------------------ : Freelance Informix Database Specialist, : Redland, Bristol, England -- graeme -- Disclaimer: The author's opinions are his own, and not necessarily those of Pyramid Technology Ltd. or Pyramid Technology Inc. --------------------------------------------------------------------------- -m------- Graeme Sargent Voice: +44 (0)252 373035 ---mmm----- Senior Database Consultant Fax : +44 (0)252 373135 -----mmmmm--- Pyramid Technology Ltd. Telex: Tell who??? -------mmmmmmm- Farnborough, Hants GU14 7PL Email: graeme@pyra.co.uk --------------------------------------------------------------------------- We have the technology. The tricky bit is learning how to use it.