DB version: 11.2.0.4
OS : Linux/Unix systems
When a block is requested by a query, Oracle looks for it in the Buffer Cache and if found, it results in a Logical read and if it does not find the Block in there it results in a physical read (disk I/O). Accessing blocks from memory is much faster than accessing blocks from the Disk. So, why is Logical I/O considered equally bad (or worse) as Physical I/O ?
Another thing I have noticed is that , in AWR report , a lot (not all) of SQLs which are listed in "SQL ordered by Gets" section (Logical I/O) are present in "SQL ordered by Reads" too. Sometimes in the same ascending order ie. SQL_IDs 2y2ujt26xj42j, a5k4qpgs4d0ap, cgrndbr5j7uqq, g1nk9u0gv0w49 are the top 4 SQLs in both "SQL ordered by Gets" and "SQL ordered by Reads" sections (screenshot shown below)
