Re: Percent Increase Behavior

From: Medic Alert <news_at_medicalert.org>
Date: 1997/03/07
Message-ID: <33204F2C.4711@medicalert.org>#1/1

MarkP28665 wrote:
>
> Oracle rounds by 5's not by one block. That is Oracle likes to make the
> extent an even muultiple of 5

That isn't what the documentation states, nor is it what actually happens in practice. If you watch the next_extent value for a table (found in sys.dba_tables) as the table grows, you will see how big Oracle wants to make the next extent when that time comes. And it always follows the rules stated in the documentation when it comes to percent free, i.e. after the second extent, subsequent extents are increased by the percent increase then rounded UP to the next multiple of the database block size. Faithfully, that is exactly what Oracle does, HOWEVER, when it actually goes to *CREATE* the next extent, it *does* appear to allocate multiples of 5 blocks rather than the size of next_extent. For example if next_extent is sitting at 12K, when the time comes to actually allocate the extent, it will be 20K, i.e. rounded UP to the next 5 block multiple.

>, but the exact amount of space used depends

> on the size of the freespace extent that is used to allocate the space for
> the extent and how much is left after subtracting the requested amount.
> If the amount of space left in the free space extents is under 5 blocks it
> is usually added to your request.
>
> Look in the database administrators guide in the section on index space
> allocation to find this.

I could not find any reference to this in the areas discussing index space allocation (which is the same technique used for table extents). I wouldn't doubt that this happens though. What is the exact name of the section you are refering to?

• TRW

Received on Fri Mar 07 1997 - 00:00:00 CST