A physical read, I/O of table or index data places the block into the buffer cache. Then we perform a logical io to retrieve the block. Hence, most physical read are immediately followed by a logical io.
There are two major types of common physical I/Os :
- reading the data in from datafiles. Doing I/O to the datafiles to retrieve index and table data. These operations will be followed immediately by a Logical IO to the cache.
The physical I/O is measured by the physical reads statistic.