Re: percent used property of table

The PCTUSED parameter defines when a block gets put back onto a freelist, or a list of blocks that can accept new rows. So your understanding of that is correct. The default value of 40 is probably not a good value for PCTUSED for many, many situations. However, if a table undergoes lots of deletes and lots of inserts, then a high value of PCTUSED will probably make such a block go on and off the freelist with a high frequency, and this can cause some performance problems. The tradeoff here is space for speed. If you want the speed, then you'll waste space. If you want the space, then you'll lose some speed.

HTH,
Brian

Richard Elliott wrote:
>
> As I understand it this means a table with the default value of 40%
> will never have a row inserted into any block for that table unless
> there is at least 40% free space in that block as a result of
> deletions. Why would the default be so low ?, and does it make good
> sense to use a much higher value if the table is one that normally has
> a lot of inserts and deletes performed against it in the normal course
> of processing?
>
> Trying to understand why some of my tables have high disk read ratios,
> and I find the same tables have lots of blocks, many many more blocks
> than can be explained by the number and length of rows.
>
> Am I on the right track ?

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