Table and index sizing

I am attempting to derive the size of the initial extent for the tables and indexes in my database. I have used the formulas in the Admin Guide, but the sizes are usually incorrect, esp. for the indexes. I know the formulas are only an "estimate", but in some cases they are not even close.

Does anyone have a formula that they use to derive the initial extent size based on the number of rows, pctfree and/or pctused, the avg. row size, etc.? I do not understand why the formulas in the book are so far off since I am getting some of the variables from a database similar to the production DB I am planning to put online.

Also, for indexes, should I keep the default pctfree value of 10%? Columns that comprise any index are either added to the index during the initial insert or during an update where the column was initially set to null, but never grow after the value is added to the index. I guess this value only comes into play when the value is added to the index for the first time, not when the row is added to the DB.

Any help is appreciated. Received on Wed Apr 05 1995 - 00:00:00 CEST