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Dereck L. Dietz wrote:
> In reading a study guide for Oracle 9i it described the data block headers.
> One item it mentions is the Row Directory which it states occupies (4 * the
> number of rows) bytes.
>
> The other book I used to get the formula I have been using to "guestimate"
> table/index sizing was the Oracle 8 DBA Manual and it just had the block
> overhead as 90 for tables and 161 for indexes.
>
> My question is probably a simple one and I apologize if it is but when it
> states (4 * the number of rows) am I correct in thinking it is referring to
> the number of rows in the data BLOCK and not the entire table?
The number of rows in the block, not the entire table.
> Another question is, isn't this a Catch-22 situation? It seems that in
> order to know what the block overhead is you need to know how many rows will
> be in the block; but in order to know how many rows will fit in the block
> you need to know the free bytes in the block (block size minus the block
> overhead).
Keep in mind that Oracle actually starts adding rows from the end of the block...towards the block header. In this way, the block header can grow if needed.
HTH,
Brian
-- =================================================================== Brian Peasland dba_at_nospam.peasland.net http://www.peasland.net Remove the "nospam." from the email address to email me. "I can give it to you cheap, quick, and good. Now pick two out of the three" - UnknownReceived on Sun Nov 26 2006 - 19:58:36 CST