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Remote Journal Filtering Reduces Network Traffic

February 7, 2012

This week's blog was written by Bruce Hansel, who is a member of the IBM i journal team.

Remote Journaling has been available on IBM i for many releases. It provides an efficient way to replicate journal entries from one system to another and is often part of a high availability or disaster recovery solution. As HA and DR have become a high priority in recent years, remote journaling has become more heavily used and multiple enhancements have been made in recent releases.

Many of the recent enhancements have been to make Remote Journaling more efficient and to provide information on the status of the Remote Journal environment. Common questions and concerns that arise around the use of Remote Journaling are often related to the communication environment. Network bandwidth, delays and retransmissions are among the top concerns.

Several options can be used to reduce Remote Journal traffic, one of the most significant is Remote Journal filtering which was introduced in 7.1 and is available with the HA Journal Performance (option 42) feature. Remote Journal filtering allows the user to eliminate sending journal entries that are not needed on the target system, reducing the required network bandwidth for Remote Journaling. Journal entries can be filtered in several ways: before image filtering, filtering by object, and filtering by program. Combinations of these can be specified as well. In each case, the number of journal entries and the amount of data sent over the network may be reduced. How much it is reduced is a function of the user's environment.

The simplest scenario is before image filtering. Typically, before images of a record in a database file are journaled because commitment control is being used. If a transaction is rolled back a before image is needed to return the record to its original state. This is appropriate but it is likely that the before image is not needed on the target system. This may be true in an HA/DR environment or in an environment where Remote Journaling is used just to send journal receivers to a target system where they are saved for backup. Not only is the amount of data sent over the network reduced but the size of the journal receiver on the target is also reduced, thereby reducing backup storage requirements.

There are some limitations on the use of journal receivers that have had entries filtered. Receivers that have had before images filtered cannot be used for RMVJRNCHG operations but they can still be used for APYJRNCHG operations. Other filtering criteria may inhibit the use of APYJRNCHG. Each of these limitations should be considered before using Remote Journal filtering and when considering the type of filtering to specify.

The additional flavors of Remote Journal filtering and the advantages and limitations of each are discussed in a technote on the IBM Redbooks website Journaling: Remote Journal Filtering in IBM System i 7.1.

More information on the use of Remote Journal filtering can be found in IBM i InfoCenter.

 

 

 

 

 

Posted February 7, 2012| Permalink

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