Re: Please define ROW CHAINING!!!

snowden_at_haven.ios.com (Roger Snowden) wrote:  >Row Chaining is the method whereby Oracle tracks block overflows. Oracle
>rows are variable length by design, although they may be fixed length in
>practice. Since Oracle permits variable length columns (varchar, etc.),
>it needs a way to allow a row to be moved if it no longer fits into a
>block. A new block is allocated and the row plopped there, with a
>forward pointer to it. It is a linked list.
>
>Not very efficient, so you want to avoid it when possible.
>
>Roger Snowden
>snowden_at_haven.ios.com
>snowdenr_at_boystown.org
>
Actually, I think this is what Oracle calls a "migrated" row. Chained rows are where the entire row it too large to fit in a single database block and therefore must always be stored in more than one block. Migrated rows can be fixed, but chained rows cannot (unless you want to change your database block size or shorten the row). They both have the same performance problems.

judie
stroup_at_ops195.lmsc.lockheed.com Received on Thu Sep 28 1995 - 00:00:00 CET