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BMC AMI Data for Db2

1 Post authored by: Darel Stewart
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REORG PLUS has several features that distinguish it from the IBM DB2 RFEORG utility.  These features improve performance, make SHRLEVEL CHANGE reorganization easier to administer, and provide the least disruptive reorganization to applications that are accessing the data.

The SHRLEVEL CHANGE option of REORG PLUS allows DB2 table space and index space objects to be available for RW access by DB2 applications during most of the reorganization.  To be truly nondisruptive, a reorganization utility must do more than simply allow application access.  If the reorganization utility competes with the application for database resources, disruption in the form of degraded performance can still occur.  To avoid this situation, REORG PLUS does not use the DB2 buffer pool, buffer manager, data manager, or work databases to accomplish its tasks.


Instead, REORG PLUS allocates data sets, staging copies of the DB2 objects and virtual storage as needed.  This additional DASD and utilization of virtual storage space eliminates the use of the DB2 resources to accomplish the reorganization.  In addition, the RID map is not a DB2 object in REORG PLUS as it is in the IBM DB2 REORG utility.  This factor prevents RID map access from interfering with DB2 processing.  By eliminating contention for these resources between REORG PLUS and the application, the reorganization can proceed in a less disruptive manner.


REORG PLUS and DB2 REORG differ fundamentally in how they determine a longlog condition.  DB2 REORG has an internal buffer that contains log records.  When this buffer becomes full, DB2 REORG processes the records.  DB2 REORG then repeats the process, making another pass at the next batch of log records.  It uses an average of the last n passes to determine whether a longlog condition exists, or whether processing can be completed by the time that is set by the DEADLINE option or by the MAXRO value. In contrast, REORG PLUS samples the arrival rate of the log records every 15 seconds to determine the rate at which the records are being applied.  It uses a weighted average of the last 15 samples to determine whether a longlog condition exists, or whether processing can be completed by the time that is set by DEADLINE or by the MAXRO value.


By using more samples and a weighted average, REORG PLUS provides the following advantages over DB2 REORG:

A greater level of accuracy in determining whether processing can be completed by the time   that is set by DEADLINE or by the MAXRO value

An increased probability that sudden changes in activity levels will not force unnecessary longlog conditions

The ability to specify LOGTHRSHLD to define when the process will end


REORG PLUS performs online partition rebalancing and alters limit key for you with no outage and without your space entering REORP status.  Online partition rebalancing is performed on the staging data sets and the ALTER commands are performed in the UTILTERM phase.  You can also use the REBALANCE command option to rebalance partitions.  By specifying REBALANCE, you can have REORG PLUS determine the limit keys for you.  To control the log apply process, you can set defaults for this process in the installation options module, and you can override these options by using the REORG command.  While the reorganization is running, you can change the log apply control options.  Depending on the values that have been set for these options, you can allow the LOGAPPLY phase to continue indefinitely, start the LOGFINAL phase, or terminate the reorganization.


To change options while the reorganization is running (up to and including the LOGAPPLY phase), you can use the XBM Utility Monitor function or the MVS console.  However, after beginning the LOGFINAL phase, REORG PLUS ignores any changes to the options.  You can use the XBM ISPF interface for a menu-driven approach to monitoring and changing a log apply reorganization, the XBM REORG PLUS online panel displays information about that reorganization job.  The panel displays the job name, step name, start date, start time, and execution phase that is currently processing.  The panel also displays the current values for the log apply control options, as well as information about the data sets that have been registered with XBM.


After REORG PLUS enters the LOGAPPLY phase, the REORG PLUS Online panel replaces the registered data set information with statistics about the log records for both the index and the table space.  These statistics include the number of records that have been applied, the number that have been queued, the arrival rate, and the application rate.  You can also enter the REORG PLUS DISPLAY option from the XBM Send New command panel to get additional information about processing of the log records.


Finally, our benchmark testing at BMC has shown that REORG PLUS continues to reduce the amount of CPU required for a reorganization and the elapsed time as compared to the IBM DB2 REORG and BMC continues to research ways to reduce those timings in future releases. 

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