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This article mainly explains "how to understand the waiting event on the database Icano". The content of the explanation in the article is simple and clear, and it is easy to learn and understand. Please follow the editor's train of thought slowly and deeply. Let's study and learn "how to understand the waiting event on the database IWeiO"!

SQL > select event#,name,parameter1,parameter2,parameter3 from v$event_name where name = 'control file sequential read'

This wait event occurs when the database needs to read the information on the control file, because the information of the control file is written sequentially, so it is also read sequentially, so it is called the sequential read of the control file. it often occurs in the following situations.

(1) backup control files.

(2) Control the information sharing of files among different instances in RAC environment.

(3) read the header information of the control file.

(4) read other information of the control file.

The wait event contains the following three parameters:

The file number of the control file that file#: wants to read information.

Block#: reads the starting block number of the control file information.

Blocks: the number of control file blocks that need to be read.

=

The process of requesting an update of a control file until the update is completed, waiting for the control file parallel write event

SQL > select event#,name,parameter1,parameter2,parameter3 from v$event_name where name = 'control file parallel write'

This wait event contains three parameters:

The number of control files to be written by files:Oracle.

The number of blocks that block#: writes to the control file.

Requests: the number of times the control file was written to the request.

In general, control file parallel write waiting does not occur very often because the control files are not updated many times. However, contention related to the control file may occur in the following cases.

When log file switching occurs frequently:

If the log file is too small, the switching of log file will occur frequently. Whenever a log file switch occurs, the control file needs to be updated, so the LGWR process waits longer for the control file parallel write event.

When checkpoints occur frequently:

When MTTR is set too short or when man-made checkpoints occur frequently, the CKPT process waits longer for control file parallel write events.

When nologging causes frequent changes to the data file:

When you modify a data file under the nologging option, you need to update the control file in order to modify the unrecoverable SCN. At this point, the server process waits for the control file parallel write event.

When the performance of the Icano system is slow:

It is best to place the control file on a separate disk space and use a bare device or direct Icano.

Control file parallel write waits are usually associated with control file sequential read waits or enq: CF-contention waits. Enq: CF-contention waits occur when multiple sessions acquire CF locks to update control files at the same time. Control file parallel write, control file sequential read, CF-contention and so on are all caused by too many control file updates or performance problems of the Imax O system.

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