Re: Chained Rows

From: Jerry Veno <jerry.veno_at_alliedsignal.com >> Should I be concerned if I have chained rows in some of my tables? <<

The standard answer is yes, however, it is not really true.

What counts is the percentage number of table row reads that require a second block to be read to be very low. The exact number is up to you, but I would not exceed 1 in 1000. One in 10,000 is better, but zero is not required for have a top performing database.

Concentrate on your heavy hit tables. It is much better to spend time eliminating a 1/2% chained rows situation from a heavily read table than eliminating 2% from a table where the row may never be read. Your maintenance time is limited.

Be aware that tables with long fields may contain rows that will not fit into one block so these rows will always chain. Check for this before you waste time re-organizing the table only to find you have as many chained rows when you finish as when you started. I include long varchar2 lengths like varchar2(1000) in this.

I hope this helps.   

Mark Powell -- Oracle 7 Certified DBA
- The only advice that counts is the advice that you follow so follow your own advice - Received on Sun May 24 1998 - 11:26:09 CDT