Re: Online Extent Sizing

Russell Pears (russell@excelsis.demon.co.uk) wrote: : I am currently running Informix Online V5.0 and am attempting to estimate the : initial and subsequent extent sizes for a *LARGE* database ( some 500 odd : tables). : Having used the algorithm in the manual I find I am getting somewhat wild : results. For starters the manual doesn't accomodate rows > pagesize. : The database in question was dbexported from SE and imported as is. The : figures I have calculated are sometimes greater, sometmes smaller than those : currently repored using tbcheck -pt. : Can someone throw some light on this ?? : Is there a better method of working these figures out ?? : Ta muchly ... : -- : Russell Pears -- Hi Russell, there are some easy rules to calculate and understand extent sizes - The default value for the first and the next extent is 16 KB - The next extent size (found in systables) is automatically doubled every 64 Extents - If two extents are physicaly next to each other, they are grouped together to one extent. This effect can be seen, when loading an entire database and the disks are not very fragmented. - The number of extents per table should not exeed 8 (INFORMIX) respectively 20 (more practically, my opinion) - The maximum number of extents is about 220, depending on the table (number of indexes, number of columns) and the PAGE SIZE ( 2KB is assumed, 4KB allows more extents) Hope it helps +-------- Herbert Birkenbach -------------------------------------------+ | CSS Fulda GmbH | | birke@css.de +49 661 93920 Justus-Liebig-Str. 2-4 | | Germany 36093 Kuenzell | +-----------------------------------------------------------------------+