Re: LRU writes

At 01:16 PM 5/2/96 GMT, you wrote: >I am trying to understand the logic of LRU writes : online 5.02.UD3 > >When I do a tbstat -F : i see > >Fg Writes LRU Writes Idle Writes Chunk Writes >0 108566 1565 244701 > >The manual says : >LRU writes : Foreground writes alert the master daemon that page cleaning is >needed. Once alerted ... > >How come that my Fg Writes is at 0 ? Foreground writes are required when the LRU queues fill up before the page cleaners wake up and clean them, typically when the system gets busy after a period of idleness. When the engine searches for a clean page and can't find one it makes one for itself via a foreground write. This is undesireable, because it means that your page cleaners aren't doing their job, and that users will have to wait while the engine cleans up the memory for them to use. That your Fg writes is zero means that your page cleaners are keeping the LRU queues clean enough for your user load. The other types of writes are more efficient, Chunk Writes being the most efficient of all (because the pages are sorted into the order in which they appear on disk.) This topic is very confusing (or it is to me, anyway) when read from TFM, but really simple when explained in class. The principles are fairly straightforward once you see the big picture and understand the terms. There are a couple of sources for good information: (here it comes...) Informix-OnLine Administrator's Guide version 5.0, dated December 1991. Part No. 000-7106 see pages 2-52, 2-71, 5-13, 7-82 but you knew that. Further: Informix-OnLine Performance Tuning by Elizabeth Suto ISBN 0-13-124322-5 dated 1995, it covers both version 5 and ODS engines it gets better... Informix-OnLine 5.0 Internal Architecture and Advanced Administration Training Manual version 5.0, dated 1995, Part No. 502-5-361-1-999999-1 page 8-221 talks about fg writes and tbstat -F You didn't know that one, did you? You may be able to get it alone, but you'd be a lot better off getting it at the training center while you took the course. (It used to be called OnLine System Administration II) I hope that helps, if not let me know what other questions you have. _____________________________________________________ | Clem Akins clema@informix.com | | International Support For best response, include my | | Informix Software, Inc name on the subject line | | Menlo Park, CA, USA Standard Disclaimers Apply | |____________________________________________________|