Figure 3-11. The v$session_wait-based OSM swswp.sql report details sessions currently posting a wait event containing latch%free. We caught three sessions waiting for latch number 116, which the second v$latchname-based query shows as being the CBC latch. We know this is a pre-10g system because the latch name is not part of the wait event.

If the Oracle release is earlier than Oracle Database 10g, the latch name is not part of the latch free wait event; therefore, additional actions must occur to determine the specific latch requiring our close attention. You have two basic options. One is to sample the system interactively based on the real-time wait event view, v$session_wait. The other option is to very carefully sample from the classic latch performance view, v$latch.

Sampling from v$session_wait is very straightforward. Figure 3-11 is based on a pre-Oracle Database 10g system v$session_wait view and displays the two key columns of utmost importance to us: event_name and p2.