The PDSMAN Performance Options improve system performance by optimizing the directory search portion of the program fetch process. The Dynamic BLDL facility caches frequently used member directory entries in virtual storage where they can be provided to subsequent requesters without incurring a DASD I/O.
Dynamic BLDL uses a separate table for each concatenation of libraries it manages. For example, the system link list would have a single table for caching directory information for all link list members, while other concatenations such as a JOBLIB or STEPLIB would have their own separate tables. In either case, the concatenation may be made up of a mixture of PDS and PDSE libraries.
When a member is accessed from a PDS, an entry for the member is created in the Dynamic BLDL table. This Dynamic BLDL table entry is used to record access statistics and to satisfy future BLDL requests.
When a member is accessed from a PDSE library, a Dynamic BLDL entry table is created but is used only for the purpose of recording access statistics. The directory search request is passed on to the operating system to be satisfied from the directory cache kept for the PDSE library.
The PDSM26 utility is used to report the contents of the Dynamic BLDL tables. On the RPTDYN and RPTDYND reports, members from PDSE libraries are followed by an asterisk (*). The bottom of the report also notes:
* PDSE MEMBERS ARE MAINTAINED IN $DYNBLDL TABLES FOR ACCESS STATISTICS REPORTING ONLY
Therefore, in the PDSM26 report:
- PDS/E library member names are followed by an asterisk.
- PDS member names have no asterisk.