Re: db_block_size

In article <01bce8e8$9e0f70c0$f3040059_at_billyv.vslabs.co.za>,

   "Billy Verreynne" <vslabs_at_onwe.co.za> wrote:
>kbolin_at_sparks.org wrote in article <878593072.19121_at_dejanews.com>...
>> We are wondering what size to make the block size when we establish our
>> first database. Does anyone have any generic "rule of thumb" for doing
>> so? Or, any ideas of what parameters to go by? It has been suggested we
>> go with 8k blocks, but really think that is too large.
>
>Small block size basically means less rows in a block. Thus the smaller the
>block size, the larger the likelihood of bad i/o performance. You should
>not make the block size smaller than what the default operating system
>block size is. You can however make it multiples of the default o/s block
>size, e.g. 16Kb, 24KB etc.for a default 8Kb o/s block size.
>
>My advice is when in doubt, stick to the defaults. :-)

Selecting a large block size also means you can cache less blocks in the SGA. If your application most of the time only needs one record from a block, selecting a large block size will waste space in your SGA.

Another point worth considering is the average length of the records in your database. If you have a lot of records larger than your block size, you will have a lot of chaining. In such a case it's worth considering a larger block size.

Stefan.

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