Maximum number of blocks for a bigfile datafile?

Question

Hello,
In 10g, when using bigfile tablespaces, the maximum size of a datafile can be between 8TB to 128TB depending on the block size (2K to 32K). The formula given to calculate the max size of a bigfile datafile is:
Maximum datafile size = db_block_size * maximum number of blocks
So my question is how do you calculate the max number of blocks? Oracle documentation states that the max number of blocks is 4,294,967,296 (4 billion) 2^32. But where do they get this number from? I read, on a different site (not Oracle), that it is the addressing scheme used in ROWID that changed permitting the possibility of addressing 4 billion blocks instead of 4 million:
This is due to a new addressing scheme Oracle uses internally. Oracle ROWID, addressing a database object stored in a traditional SMALLFILE tablespace, divides the 12 bytes thusly: 3 bytes for the Relative File#, 6 bytes for the Block# and 3 bytes for the object. The same rowid addressing an object stored in a new BIGFILE tablespace uses the 9 bytes to store the Block# within the unique file, as there is no reason to use the 3 bytes for the Relative File# since there is only one file in that tablespace. Thus the new addressing scheme permits up to 4Gblocks (4,294,967,296) in a single data file and the maximum file size can reach 8 TB for a blocksize of 2K and 128 TB for a blocksize of 32K.
But, even with this explanation, 4 billion still makes no sense because using 9 bytes equates to 2^72 addressable blocks, not 2^32. Am I missing something?
Thanks,
Mark

Answer 1

Thanks for the answer.
I'm almost tempted to accept the explanation that the 4,294,967,296 addressable blocks is a 32bit platform limitation... Do you or anyone know of any official Oracle documentation explaining where they get this magic number from?