Re: PCTFREE and PCTUSED

Hi!

> I'm not entirely in agreement with the quote (that's a different story)
but
> notice there is no mention of PCTFREE.

Yes, this is a deficiency of documentation. PCTFREE is still used and needed in ASSM segments. As you said, value for it can not be tuned automatically, since Oracle doesn't have slighest idea about nature of future data (there's still no time machine in Oracle ;)

>
> ASSM is designed to automatically determine whether or not a block should
be
> considered for inserts. It does this by using a sequence of bitmaps to
> describe the "fullness" of a block. There are different levels of fullness
> empty 0-25, 25-50, 50-75 and 75-*full*. However what does *full* actually
> mean or at what point does Oracle no longer consider the block suitable
for
> inserts.

Note that ASSM bitmaps track "freeness" not "fullness", to be correct in terminology. Thus the freeness statuses for a table are full, 0-25% free, 25-50% free, 50-75% free, 75-100% free and unformatted as well. (it's probably more like 0-24% and 25-49% etc, but this is not so important)

There are 4 freeness bits per block in ASSM table, but for LOBs and indexes there are less. For an index, for example, you only have to state whether a block is "insertable" or not, there's no need for multiple different freeness bits.

> Hope this makes some sense :)
>
> Cheers
>
> Richard

You probably don't need this information but you can download my presentation about Freelists vs. ASSM internals, which I presented at OracleWorld Paris, from my homepage http://integrid.info

Tanel.

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Author: Tanel Poder
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