UDS/SQL uses the FASTPAM access method in the independent DBH for all files, except the following:
Realms with a 2-Kbyte page format
Database files located on shared or protected private disks (SPD or PPD)
Database files located on multiple public volume sets (MPVS).
These files are still processed by UDS/SQL with the UPAM access method. The linked-in DBH only used the UPAM access method.
Access with FASTPAM is more efficient than with UPAM, since some access paths are prepared for FASTPAM and some areas are maintained in resident memory.
In order to create memory-resident areas, the BS2000 user ID will need to have FASTPAM privileges. The BS2000 command SHOW-USER-ATTRIBUTES can be used to check whether the BS2000 user ID has the required privileges. The DMS-TUNING-RESOURCES item must be set to the value *EXCLUSIVE.
FASTPAM may be used even if the BS2000 user ID does not have FASTPAM privileges, but no memory-resident areas can be maintained in that case. This also applies when the BS2000 user ID has the required FASTPAM privileges, but when all I/O areas cannot be made memory-resident (due to a lack of available main memory).
If the loading of UDS/SQL is rejected under the BS2000 user ID despite an adequate value for RESIDENT PAGES, the maximum number of resident main memory pages allowed may need to be raised accordingly by the BS2000 system administrator (using the BS2000 command MODIFY-SYSTEM-BIAS). The currently set maximum value (CORE) can be checked with the BS2000 command SHOW-SYSTEM-STATUS via the parameter INFORMATION=*SYSTEM-PARAMETERS.
You specify the required number of resident pages via the RESIDENT-PAGES operand when the DBH is started (START-UDS-DBH or START-EXECUTABLE-PROGRAM command). You must specify a minimum value and a maximum value.
If you specify a minimum value = 0, UDS/SQL will start up in any case, but possibly with degraded performance. If the specified minimum value is > 0, UDS/SQL is started only if the minimum requirement can be satisfied.
In order to calculate the maximum value, the sizes of the 4-Kbyte and 8-Kbyte buffer pools, in particular, must be taken into account. For example, the approximate value for a total of n databases would be
300 Kbyte + n*100 Kbyte + 1,1 * (sum of the sizes for the 4-Kbyte and 8-Kbyte buffer pools)
Since the 4-Kbyte system buffer pool is at least 1.3 Mbytes in size, the minimum requirement (for an attached database) would be 1.83 Mbytes = 458 resident 4-Kbyte pages.
If the return code UDS0600 is output with the insert USER LIMIT EXCEEDED on starting the DBH, then the DBH has not been assigned enough resident pages. The reason for this can be that the maximum value specified for RESIDENT-PAGES at startup was too small, but also that the system could not make enough pages available.
More information on the FASTPAM access method can be found in the manual “Introductory Guide to DMS”.