The amount of time it takes to retrieve data blocks is proportionate to the number of extents in the table. Ideally, a table should have one to three extents. Run this script from sqlplus to get those segments (tables or indexes) that have a surplus of extents. Here
What is Metadata?
What is metadata? Well, It’s an odd concept to wrap your head around. Metadata is essentially the secondary layer of data that tracks details about the “regular” data. The regular