Fast Path 64-bit buffer manager

The Fast Path 64-bit buffer manager autonomically controls the number and size of Fast Path buffer pools, including buffer pools for data entry databases (DEDB), main storage databases (MSDB), and Fast Path system services. The Fast Path 64-bit buffer manager eliminates the need for system programmers to manually set buffer pool specifications during system definition.

The Fast Path 64-bit buffer manager also places the DEDB buffer pools above the bar in 64-bit control region private storage, which reduces the usage of ECSA storage.

When the Fast Path 64-bit buffer manager is used, the following items continue to be managed in ECSA storage:

• Fast Path buffer for MSDB databases
• Buffers for inserting sequential dependent (SDEP) segments
• Buffers for system services
• Buffer headers
• Internal IMS work areas for FLD calls and MSDBs

When the Fast Path 64-bit buffer manager is not used, the number and size of Fast Path buffer pools must be set during system definition by using the DBBF, DBFX, and BSIZ execution parameters, all Fast Path buffer pools are placed in 32-bit ECSA storage, dependent region access to overflow buffers is serialized, and, after IMS is started, the number and size of the Fast Path buffer pools cannot be changed without stopping and restarting IMS.

The Fast Path 64-bit buffer manager is enabled by one parameter, FPBP64, in the Fast Path section (SECTION=FASTPATH) of the DFSDFxxx PROCLIB member. When enabled, the Fast Path 64-bit buffer manager allocates additional buffer subpools when needed. Also, if a database is added to the online IMS system and none of the active buffer subpools can accommodate the CI size of the database, the Fast Path 64-bit buffer manager allocates a new buffer subpool of the appropriate size.

Because the Fast Path 64-bit buffer manager places the DEDB buffer pools in 64-bit storage, more buffer pools can be allotted to each dependent region that issues calls against a DEDB. For each additional buffer pool, the usage of ECSA storage increases only by the amount needed for the buffer header. The more buffers that a dependent region has available, the more work an application program can perform between checkpoints.

The Fast Path 64-bit buffer manager also enables multiple dependent regions to access overflow buffers in parallel, eliminating contention among dependent regions for overflow buffers.

The maximum number of buffers that can be allocated to a dependent region, both normal and overflow buffers combined, is determined by the NBA and OBA parameters in the dependent region definition and is not limited by the Fast Path 64-bit buffer manager.

When the Fast Path 64-bit buffer manager is enabled:

• You can change database CI sizes without having to adjust the buffer sizes to match. If no active buffer subpools can accommodate a new or changed CI size, the Fast Path 64-bit buffer manager automatically allocates a buffer subpool with the correct CI size.
• You can display statistics for Fast Path buffers by issuing the IMS type-2 command QUERY POOL TYPE(FPBP64).
• You can capture usage statistics for the Fast Path 64-bit buffers by issuing the command UPDATE IMS SET(LCLPARM(FPBP64STAT(Y))). IMS captures the usage statistics for each unit of work in a dependent region and writes the statistics to the online log data set as X'5945' log records, which are mapped by macros DBFL5945 and DBFBPND6.
• You can see if the logging of Fast Path 64-bit buffer usage statistics is enabled in an IMS system by using the QUERY IMS SHOW ( ALL | LOCAL ) command.