Block Header Size Confusion

From: Dereck L. Dietz <dietzdl_at_ameritech.net>
Date: Sat, 25 Nov 2006 21:01:10 GMT
Message-ID: <qa2ah.254$Py2.90@newssvr27.news.prodigy.net>

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?

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).

Thanks. Received on Sat Nov 25 2006 - 15:01:10 CST