compress for OLTP

[BeefStu]

I want to enable "COMPRESS FOR OLTP" on some of my tables. Before doing
so I want to do some a lot of testing.

What I planned on doing is having 2 tables with the same layout one with
COMPRESS FOR OLTP and the other without that option and loading the same
data into both tables.

Is there a query I can use that will show me the amount of space saved or
the amount of data blocks used for each table?

My understanding is that if duplicate data is encoutered in the same block when COMPRESS FOR OLTP is enabled it keeps one copy of the value for
the column within the block and the other duplicate values will have pointers. which will point back to the data.

In addition, are there any things I need to watch out for, Ie I think I
read this does not work for BLOB's, can I use an alter table command to
compress the table if it has not been compressed already.

Thanks in advance to all who answer

[vnktummala]

yes ... you can query from dba_segments to check how many blocks, extents each segment has occupied.

Thanks,