Re: slow query - index usage question

From: Tanel Poder <tanel_at_@peldik.com>
Date: Sun, 23 Mar 2003 16:22:27 +0200
Message-ID: <3e7dc264$1_2@news.estpak.ee>

> On the constraint thing, I believe it's stored outside the table, whereas
a
> NOT NULL on the column is a semaphore in the table header. Might be wrong

Hi,

in segment header, there's no data saved about the logical structure of segment, e.g. table columns, not null constraints. These remain in data dictionary.

An one-block segment header contains HWM information for segment, extent map, freelist head and tail pointers probably some additional information as well, but no information about the structure of information inside the data blocks.

More, if you use ASSM, LMT, FREELIST GROUPS, or have more extents in segment than the extent map in header block can handle, then the situation will be different. For example, with LMT we don't have extent map in segment header block anymore and with freelist groups we have additional blocks for specifying freelists.

Tanel. Received on Sun Mar 23 2003 - 08:22:27 CST