Speed

Oracle memory structures mutate rapidly, and SQL is not suitable for fast and repetitive access. For example, in an Oracle instance with many user connections, you may not be able to sample the V$SESSION_WAIT view 50 or more times per second. But it is not a problem for an external C program to do 50 or more read iterations per second on a memory region. (The critics of the SQL and PL/SQL sampling methods think they need such a high frequency sampling. We think it is overkill for sampling. Oracle Database 10g only samples once every second.) An external C program can read a memory region faster than SQL, provided there is no need to join and sort data from various memory structures.

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