Re: Oracle b-trees

On 30 Dec 1997 16:57:42 -0800, joelga_at_pebble.ml.org (Joel Garry) wrote:

>
>See the discussion about the Truncate command in your Server Administrators
>guide. When you delete records in a table, the storage is still allocated
>and the full table scan might have to read all those empty blocks. The
>delete also can mess up subsequent ads because the freed up blocks are
>added to the bottom of the free list.
>

When a table is truncated, the high water mark is reset to the beginning of the first extent.

Full table scans read only to the high water mark, regardless of the space allocated to the table.

A table with a 1 gig extent that has been truncated can be read by a full table scan in a fraction of a second.

Just deleting all of the rows in a table will however cause a full table scan to read a lot of nothing. Received on Thu Jan 08 1998 - 00:00:00 CST