Management of and accesses to the file catalog TSOSCAT are carried out internally by the Catalog Management System (CMS). For a functional description and further suggestions for tuning, see section "Creating system files".
The system parameters BMTNUM and CATBUFR should always be considered together. When deciding which values to assign to these parameters, you must take into account the number of pubsets with which the system is to be run (cf. CATBUFR).
Parameter name | Value range | STD value |
BMTNUM | 0 ... 255 | 32 |
This parameter defines the number of I/O buffers and Buffer Management Tables (BMT) for the catalog management system (CMS). This number of buffers is created once for each pubset and once globally for all private disks and Net Storage volumes.
Each block of the TSOSCAT file can contain max. 13 file entries or 18 JV entries. For each CMS I/O buffer (4096 bytes für pubsets, 2048 bytes for private deisks and Net Storage Volumes) a table (BMT) is created (approx. 178 bytes). It is used for managing the current status of the block in the buffer.
The default value for BMTNUM is 32. For pubsets, this is also the lowest possible buffer number. Values from 0 to 31 are only applied for private disks.
Each increase also increases the probability that CMS will find a file entry or JV entry without a physical input operation being carried out. The positive effect of this strategy is particularly noticeable in the case of frequent access to adjacent catalog entries and thus to one and the same catalog block.
Parameter name | Value range | STD value |
CATBUFR | N/Y | N |
If this parameter is set to Y, the CMS buffers and the BMTs will be created as resident (in class 3 memory).
If it is set to N (default), they will be created as pageable (in class 4 memory).
The pubset-specific setting of the number of CMS buffers and their memory class is carried out using the commands
/ADD-MASTER-CATALOG-ENTRY /MODIFY-MASTER-CATALOG-ENTRY /IMPORT-PUBSET
and the operands NUMBER-OF-BUFFERS and RESIDENT-BUFFERS.
Defined values are sought in the following order:
Explicit parameter specification in /IMPORT-PUBSET
Specification for /ADD-MASTER-CATALOG-ENTRY or /MODIFY-MASTER-CATALOG-ENTRY
Specification via the system parameters BMTNUM and CATBUFR
If neither private disks nor Net Storage volumes are used, buffer allocation for private disks can be prevented with BMTNUM=0. For Pubsets, the minimum number of 32 buffers stays effective. With /MODIFY-MASTER-CATALOG-ENTRY (for home and paging pubsets) or /IMPORT-PUBSET the number of CMS buffers and their storage class can also be specified differingly.
The size of the address space requirement per pubset or of the private volumes for the CMS buffers can be calculated using the following formula:
CMS buffer (bytes) = (x + y) * Number of buffers + 384
x = 4096 for pubsets; x = 2048 for private volumes
y = 178 for pubsets; y = 200 for private volumes
If, for example, with smaller systems a large number of memory-resident buffers are created, the catalog operations will be faster but this advantage may be offset by an increased paging rate. If the catalog is accessed frequently, use of the software product SCA (Speed Catalog Access) is imperative.