A conceptual article on Optimization

So that we can make a persuasive judgment.

Description

Wait for "SQL * Net message from client". The SQL * Net package that receives the statement request "parse/execute.

Parse the SQL * Net package.

Wait for "latch free" to get a "library cache" latch.

Search for SQL statements in the Shared Pool, find matched, release latches, and create links to the shared cursor. Start execution.

Wait for "db file sequential read" because we need a data block that is not currently in the buffer cache. For example, wait for one IO to complete.

Read data blocks and start execution. Construct an SQL * Net Package and return the information containing the first line of data to the user.

Wait for "SQL * Net message to client" to confirm that the SQL * Net package has been delivered.

Wait for "SQL * Net message from client" to make the next request.

Description

The session is waiting for a specific event. (In Oracle 9.0.1, when the session is not waiting yet, V $ SESSION_WAIT shows that WAIT_TIME is 0, but due to the Bug: 2117360, the CPU may be used. V $ SESSION_WAIT.STATE displays a value other than "WAITING .)

CPU session is being used. The events listed are the last events that the session waits. WAIT_TIME indicates the time when the session waits for the last event.

-1 session needs to wait for a short time.

-2 do not know how long to wait (TIMED_STATISTICS = false ).

> 0 indicates the actual wait time in 10 ms.