Re: Please define ROW CHAINING!!!

From: Glenn Stauffer <stauffer_at_swarthmore.edu>
Date: 1995/10/02
Message-ID: <stauffer-0210951043300001_at_stauffer.swarthmore.edu>#1/1


In article <44hujn$ar2_at_dingo.cc.uq.oz.au>, gordonh_at_acslink.net.au wrote:

->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.
-

You can sometimes fix chaining by changing the pctfree value. You would do this by determining a better pctfree, rebuilding the table using the export-drop-create-import method, and rechecking with analyze table. If you can't get rid of chaining this way, the data is too long to fit into a database block and you would need to investigate recreating the database with a larger block size.

Performance degrades because the database must read two blocks to obtain the data for a chained row as opposed to one block read for a row that isn't chained.

--



Glenn Stauffer
Received on Mon Oct 02 1995 - 00:00:00 CET

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