BCF Physical Logger

It can provide significant performance improvements and reduce overall resource usage during the physical logging process. It can be used independently of the execution controller.

The BCF Physical Logger provides all the services requested by the IMS Logical Logger:

• Opening the log data set
• Closing the log data set
• Reading the log data set
• Writing the log data set
• Forcing the end-of-volume (EOV) on the log data set
• Terminating operations in case of emergency (ESTAE)

The BCF Physical Logger incorporates the following features:

• • Buffered device support
  • Discard logging support
  • Dynamic backout log
  • SLDS duality support
  • Execution statistics

Buffered device support

The BCF Physical Logger removes the IMS restriction that buffered devices (3480 and 3490 tape drives) must use tape write immediate (TWI) mode when used as batch logging devices. This restriction prevents you from taking advantage of the performance improvements offered by buffered tape devices. BCF can write to these devices in buffered mode, yet still ensure data integrity. Through device monitoring and synchronization techniques, the Physical Logger provides the IMS Database Manager with write ahead log tape (WALT) support for database integrity.

Discard logging support

For some batch jobs, it may be desirable to bypass the logging of database changes.

However, DBRC requires batch logging if the database is registered and DBRC is active. Without BCF, to bypass logging you must turn off DBRC during the batch job—opening a window for database integrity exposures. With BCF, the BCF Physical Logger can discard the log blocks received from the IMS Logical Logger but inform IMS that the log block was written normally. It also issues the notifications to DBRC that help ensure data integrity.

Dynamic backout log

The BCF Physical Logger can create an in-memory dynamic log for use with the IMS dynamic backout process.

The IMS dynamic backout process can handle certain classes of DL/I pseudo abends. It is particularly useful in a block-level sharing environment.

The dynamic log data set written by BCF contains only the database log records that have been written since the last application checkpoint. BCF stores the dynamic log data set in extended private memory or in an MVS/ESA data space.

When using the BCF dynamic log, you can take advantage of the IMS dynamic backout capability while writing the log data sets to tape media. Without BCF, the logs must be written to DASD for the IMS dynamic backout process to work.

When using BCF dynamic log and writing the log data sets to DASD, BCF can write the log blocks in true variable blocked format. It is not necessary to pad the log blocks to the maximum block size to emulate the fixed blocked format required by the IMS dynamic batch backout process. Writing the log blocks in variable blocked format can result in reduced DASD usage for batch job steps that log to DASD and request dynamic backout.

SLDS duality support

If the job step JCL must request dual logging, the BCF Physical Logger can attempt to provide SLDS duality. It writes a specified number of blocks to each SLDS prior to forcing an end-of-volume condition on both log data sets. This process is consistent with the process used by the IMS Archival utility.

Execution statistics

The BCF Physical Logger collects and reports statistics to help you monitor and tune the performance of batch programs.

The BCF Physical Logger can analyze these statistics and notify you when you can tune the job’s database buffer pools to improve logging to buffered tape devices. In some instances, this feature can also allow you to bypass application performance tuning unless it is really necessary.

The performance improvements provided by the BCF Physical Logger can be lessened by factors such as database buffers, application design, log block size, and other factors that are specific to an installation.