Monitoring I/O

The I/O charts show I/O statistics collected from all database clients. The I/O wait time for a database process represents the amount of time that the process could have been doing useful work if a pending I/O had completed. Oracle Database captures the I/O wait times for all important I/O components in a uniform fashion so that every I/O wait by any Oracle process can be deduced from the I/O statistics.

The Latency for Synchronous Single Block Reads chart shows the total perceived I/O latency for a block read, which is the time difference between when an I/O is issued and when it is processed by the database. Most systems are performing satisfactorily if latency is fewer than 10 milliseconds. This type of I/O request is the best indicator of I/O performance for the following reasons:

• Write operations may exhibit good performance because of write caches in storage.

• Because multiblock I/O requests have varying sizes, they can take different amounts of time.

• The latency of asynchronous I/O requests does not represent the full I/O wait time.

The other charts shown depend on your selection for I/O Breakdown, as described in the following sections:

• Monitoring I/O by Function

• Monitoring I/O by Type

• Monitoring I/O by Consumer Group