Wait Event – read by other session

This event occurs when a session requests a buffer that is currently being read into the buffer cache by another session. Prior to release 10.1, waits for this event were grouped with the other reasons for waiting for buffers under the ‘buffer busy waits’ event. Wait Time: Time waited for the buffer to be read by the…

Wait Event – rdbms ipc reply

This event is used to wait for a reply from one of the background processes. Wait Time: The wait time is specified by the user and is indicated by the parameter timeout.   Parameter Description from_process The background process for which the session is waiting. The wait is for a reply to an IPC message sent by…

Wait Event – rdbms ipc message

The background processes (LGWR, DBWR, LMS0) use this event to indicate that they are idle and are waiting for the foreground processes to send them an IPC message to do some work. Wait Time: Up to 3 seconds. The parameter timeout shows the true sleep time.   Parameter Description timeout The amount of time that the session waits…

Wait Event – log file parallel write

Writing redo records to the redo log files from the log buffer. Wait Time: Time it takes for the I/Os to complete. Even though redo records are written in parallel, the parallel write is not complete until the last I/O is on disk.   Parameter Description files Number of files to be written blocks Number of…

Wait Event – log buffer space

Waiting for space in the log buffer because the session is writing data into the log buffer faster than LGWR can write it out. Consider making the log buffer bigger if it is small, or moving the log files to faster disks such as striped disks.

Wait Event – Log archive I/O

Used local archiving of online redo logs (for a production database) or standby redo logs (for a standby database). When the archiving process exhausts its I/O buffers because all of them are being used for on-going I/O’s, the wait for an available I/O buffer is captured in this system wait event.

Wait Event – library cache: mutex X

Library cache mutexes protect hash buckets within the shared pool. Each hash bucket contains a number of cursors. The mutex must be held in exclusive mode before any of the structures that it protects can be changed. This wait event is often associated with high parse activity.

Wait Event – library cache load lock

The session tries to find the load lock for the database object so that it can load the object. The load lock is always obtained in Exclusive mode, so that no other process can load the same object. If the load lock is busy the session will wait on this event until the lock becomes…