Re: Large initial extent after import

On Sat, 14 Nov 1998 13:20:21 -0000, Neil Hulin wrote:

>>With correctly chosen parameters the number of extents per segment can
>>have practicaly *no impact* on performance. "Single extent per segment
>>is a must for good performance" is nothing but an old DBA mith that
>>has nothing in common with reality!
>
>
>OK - your view is your view - call me a dinosaur.
>
>>The only impact a large number of extents per segment can have on
>>performance is when you are dropping the segment - in that case you
>>realy will have to wait for a long time if you have a few thousand of
>>extents instead of 20 or 30.

I've been thinking about this problem some more but I still don't _understand_ the implications. Apparently, the number of blocks will be the same no matter what size of extent you choose (i.e. you can create 11.000 extents of 6 blocks or 6 extents of 11.000 blocks). So you basically choose to:
a) keep the number of blocks (per extent) down, or b) keep the number of extents down.

Can anybody _explain_ which option is better, I mean, it is pretty easy to understand that chained rows will have impact on performance, but I still don't see any reason to choose either option (apart from the performance gain Neil noticed, well, can anybody explain that one?).

Thanks
--
Jan
pantah_at_commonsense.a2000.nl
(replace "commonsense" by "speed" to reply) Received on Sat Nov 14 1998 - 12:07:27 CST