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MAX_COMMIT_PROPAGATION_DELAY(转)

原创 Linux操作系统 作者:tochar 时间:2007-07-26 00:00:00 0 删除 编辑

MAX_COMMIT_PROPAGATION_DELAY

Parameter type

Integer

Default value

700

Parameter class

Static

Range of values

0 to 90000

Real Application Clusters

You must set this parameter for every instance, and multiple instances must have identical values.


Caution:

Change this parameter only when it is absolutely necessary to see the most current version of the database when performing a query.


MAX_COMMIT_PROPAGATION_DELAY is an Oracle9i Real Application Clusters parameter. This initialization parameter should not be changed except under a limited set of circumstances specific to the cluster database.

This parameter specifies the maximum amount of time allowed before the system change number (SCN) held in the SGA of an instance is refreshed by the log writer process (LGWR). It determines whether the local SCN should be refreshed from the lock value when getting the snapshot SCN for a query. Units are in hundredths of seconds.

Under very unusual circumstances involving rapid updates and queries of the same data from different instances, the SCN might not be refreshed in a timely manner. Setting the parameter to zero causes the SCN to be refreshed immediately after a commit. The default value (700 hundredths of a second, or seven seconds) is an upper bound that allows the preferred existing high performance mechanism to remain in place.


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