Originally posted by abhaysk
When DROP, TRUNCATE, ALTER is issued, actual clean up of data or whatsoever will not happen.
Oracle will only drop in the POINTERS pointing to the Mem Locations,
Oh, it takes much more for Oracle to drop a database object than just to "drop some poiters pointing to mem locations". It takes *many* updates/deletes/inserts into data dictionary tables and/or fixed tables to drop a single table.

For example, you drop a table, and oracle has to do:

- delete one row from OBJ$
- delete one or more rows from COL$
- probably delte some rows from IND$
- delete one or more rows from SEG$
- delete one or more rows from UET$
- insert one or more row into FET$
- probably delete some rows from IDL_* tables
- ...

And all those tables are quite heavily indexed and I have named just a few dictionary tables (perhaps less than 10%) that must be taken care of just for one simple DROP TABLE statement. So you can immagine all this work might take quite a significant amount of time. Not to speak about all the work that SMON has to perform afterwards to actually clean up the space in tablespaces.

So it is much more to do than just to drop few "pointers".