WAITED UNKNOWN TIME: Last wait time is unknown; perhaps instance parameter timed_statistics is false

Suppose we wanted to take a closer look at a particular session. Continuing our example based on Figure 2-8 and Figure 2-9, look closely at Figure 2-10. This is a very simple script based on v$session_wait. In this example, we caught session 205 in the middle of a wait and the details are exposed. Figure 2-10 clearly shows session 205 is currently waiting for an operating system multiblock read to complete. And we also know that 16 blocks are being requested (P3), the first block's file number is 4 (P1), and its block number is 12925 (P2).

Figure 2-10. This script is based on the v$session_wait view. This is easy to tell because the output contains the parameter columns. Session 205 is currently waiting for the operating system to retrieve 16 blocks.