Re: Magic number ( 5 * DB_BLOCK_SIZE )

Jonas M wrote:
>
> Hi
>
> While studying by Oracle Books , I've come accross this tip several times:
>
> you should use uniform extent sizes : multiples of 5 * DB_BLOCK_SIZE
>
> Why do they insist on this value ? I thought the ideal situation would be to
> fit all my data ( from a regular table ) in just one extent...
> isn't that so ? Is it better to have several extents , and get the data
> spread among them ?
>
> Thanx in advance

Oracle rounds sizes to this multiple... although I'm a fan of making all extents a multiple of the max single OS read size (typically in the order of 128-256k).

One thing I cannot stress enough is that "one extent" is a myth. What you want to have is all extents the same size (per tablespace that is). Check out locally managed tablespaces for some more info.

hth
connor

-- 
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Connor McDonald

http://www.oracledba.co.uk

"Some days you're the pigeon, some days you're the statue..."