Here is a breakdown of the life of an Oracle shadow process and where it might be waiting as it
lives. This comes from Oracle Doc ID 61998.1 and shows what’s happening in less than one
second within Oracle.
State Notes
IDLE Waits for “SQL*Net message from client” (waiting for the user).Receives the SQL*Net packet requesting “parse/execute” of a statement.
ON CPU Decodes the SQL*Net packet.
WAITING Waits for “latch free” to obtain the “library cache” latch. Gets the library cache latch.
ON CPU Scans the shared pool for the SQL statement, finds match, frees
latch, sets up links to the shared cursor, etc., and begins to execute.
WAITING Waits for “db file sequential read”; we need a block not in the cache
(wait for I/O).
ON CPU Block read from disk complete. Execution continues. Construct SQL*Net packet with first row of data to send to client and sends.
WAITING Waits on “SQL*Net message from client” for acknowledgment packet received.
IDLE Waits for next SQL*Net message from client
Thank Richard Niemeic for good information from oracle book "oracle performance tuning tip and technique"
Hope this help you:D
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