How do I get the Block Header Size in Oracle?

Question

I'm trying to calculate the size of a few tables as stated here, but I can't find the block header size variable

How do I get it? Is it some kind of formula?

I'm using Oracle 10g

Answer 1

This site has a good discussion on the format of the block header: http://www.adp-gmbh.ch/ora/concepts/db_block.html. Basically the block header = fixed header + transaction header + table directory + row directory. Here are the individual pieces:

fixed header = 57 bytes

transaction header = between 23*inittrans and 23*maxtrans

table directory = 4*number of tables (usually 1 unless you're using clusters)

row directory = 2*stored rows

In short while you can come up with a rough estimate, it's not a fixed size for each data block.

Answer 2

This page (for 10g) says it's 57 bytes.