Table Scans/Table Fetch (Oracle)

This section of the monitor shows how database data is accessed.

A full table scan occurs when Oracle must read all data blocks of a table from disk. When the amount of data being read is small (short tables), this type of access is preferable. When the amount of data being read is large (long tables), index access may be preferable.

When data from a table is accessed via an index, Oracle performs the actual lookup using the rowID of the block holding the data. Access via this kind of index is normally very fast.

If a data record does not fit in one Oracle data block (whose size is determined by db_block_size ( DB_BLOCK_SIZE (Oracle))), it must be continued in another block (data chaining).