Also check the amount of disk reads are being done.
If it has to read all the data off disk, (say 6GB) then at 5ms per 16k page would take 43 mins just to read the data. The second alter table could read from cache and take just a couple of mins.
This is an interesting test. I will schedule this to see how long it takes to do each individual process. I also assume that the rebuild index does not do the same work as say a reorg rebuild table.
Thanks
