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The CCILGR/Assured Delivery component of CAICCI is required for sites that run ACF2/CPF. CCILGR is built upon the fundamental mechanisms of VSAM file access, and is a store and forward application. As such, data is received, written, and stored in the VSAM database then read before being sent out. When the data is sent it remains in the VSAM file until the local CCILGR receives confirmation from the data recipient that the data arrived intact. When confirmation is received, CCILGR deletes the record from the database. ACF2/CPF command propagation requires its own response to prevent duplicate data. Due to the constant reads, writes, and deletes, the CCILGR database is dynamic.
In order for Assured Delivery to guarantee that data is delivered and received securely, with integrity, and in the proper sequence, the product utilizes keyed sequential file access to VSAM. The keys are linked to the time the record was written, so every key is unique, and cannot be duplicated or reused. Because the access is keyed and sequential, inbound records are written to the end of the file and must be read again before being sent to their destination. Additionally, every read must begin at the top of the file and traverse all existing records until the one to be processed is encountered. Over time the database fragments with CA/CI splits, and if the amount of data being delivered within a sysplex of many systems is significantly large, there may be a performance impact.
One of the major reasons to reorganize the CCILGR VSAM file is when Control Areas become unusable. If a receiver becomes unavailable or is unable to keep up with the volume of messages, the messages will remain in the VSAM file for a long time, eventually causing Control Areas to fill up. When a control area becomes full, it is associated with a specific date and time range, and VSAM will not reuse that control area even after all the records in it have been delivered to the receiver and deleted from the file. The only way to reclaim those Control Areas is to reorganize the file.
With z/OS 1.12, a new VSAM option became available called CA Reclaim. With this option enabled, when a Control Area becomes empty, it will no longer be associated with a specific date and time range, and can be used to store newly created records. This will eliminate the need for frequent reorganizations. Even with this option enabled, the CCILGR VSAM file should still be reorganized periodically, perhaps weekly or monthly.
The CA Reclaim option is disabled by default on a system level, but it is enabled by default for all KSDSs , without having to redefine the data set. To turn on CA Reclaim at the system level, member IGDSMSxx in SYS1.PARMLIB must be updated to contain the new parameter “CA_RECLAIM(DATACLAS)”. This will allow VSAM to reclaim newly emptied Control Areas in all VSAM files. See the IBM z/OS MVS Initialization and Tuning Reference manual for more information.
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