I have inherited a historical database which is in excess of 150gb it has partitioned tables and indexes, however it is severly oversized and is using about 30GB. What is the best plan of action or options I have in order to downsize this database.
You are making the assumption that the space being used is at the beginning of the file. I must check DBA_EXTENTS to see where the extents in the file are located. Looking at BLOCK_ID and BLOCKS to see the starting block and the total number of blocks in the extent respectively.
If you are on 8i you can move tables (or table partitions) to new locally managed tablespaces and rebuild your indexes in new locally managed tablespaces. Drop your old tablespace when all contents are transfered.