Re: Raw partitions / cooked files

In <1812@rand.mel.cocam.oz.au> shaneb@mentat.mel.cocam.oz.au (Shane Booth) writes: >We have OnLine databases (version 5.0) on a Sun SPARCstation 10, one on a >raw partition and one on a cooked file. >For a query involving a join on two tables, where one of the tables is very >small (~10 rows) and we do a sequential scan through the second table >(~40Mb and ~50000 rows), the raw partition takes 2.6 times as long (on >average) as the cooked file to execute the query. I just can't work out why? >It's supposed to be the other way 'round isn't it? >Details: SPARCstation10 Model 30, OnLine version 5.00.UC3. It's probably the effect of your UNIX buffers. Unless you are relinking your kernel or increasing OnLine buffers for the raw tests, you are allocating more memory to buffering on your cooked file tests than you are on your raw disk tests. This is the only way to get an "apples with apples" comparison, as in the production environment you would either de-allocate your UNIX buffers, or they would be busy doing something else, and you wouldn't see the cacheing effect your tests appear to be experiencing. The other effect that you may be seeing could also be an artificiality introduced by the test environment. If you are testing an unfragmented table on an unfragmented filesystem, you will see much better performance from a cooked file than you would see in real life. With a raw file however, your tables will stay unfragmented in real life (assuming sensible extent sizes) as there is no filesystem to introduce fragmentation within an extent. Other things to consider: Are the two tables on the same disk/disk type? If so, are they different levels of contention from UNIX? 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.