28 IMS in the Parallel Sysplex Volume II: Planning the IMSplex
READ_DATA request
Before IMS reads a block of data into its buffer pool, it must first tell the Coupling Facility
which block of data it will read and which buffer it will put that data in. This is called
registering
interest
in a data item and is necessary so that, if another IMS updates that block, the other
IMS’s buffer can be invalidated. This XES cache service is the READ_DATA request. It
causes a directory entry to be created (or updated, if it already exists). If an existing directory
entry points to a data entry in the structure when the READ_DATA request is made, that block
will be automatically read from the CF into the buffer identified on the request without further ...