Parameter name | Value range | STD value |
EAMMEM | 0...2730 | 0 |
EAMMIN | 4...64512 | 3000 |
EAMSEC | 1...64512 | 200 |
EAMSIZ | 4...64512 | 64512 |
These parameters define the size of the SYSEAM file. They are valid for all :catid:SYSEAM files if they are created on several pubsets and if nothing else is defined in the MRSCAT entry for each pubset. In addition, the allocation unit specified when the pubset was created with SIR is considered depending on the data format (K, NK2, NK4).
The SYSEAM file is managed in EAM allocation units. When a DMS allocation unit is 3 PAM pages, the EAM allocation unit is also 3 PAM pages; in the case of all other DMS allocation units the EAM allocation unit is 4 PAM pages. The value of EAMMIN defines the minimum size. If necessary, it is extended by the value of EAMSEC (number in EAM allocation units) until the maximum size of 64512 EAM allocation units is reached. Should the SYSEAM file shrink (e.g. in the case of /DELETE-SYSTEM-FILE SYSTEM-FILE=*OMF or /EXIT-JOB), it is reduced in increments of 8 allocation units, but does not go below the value of EAMMIN.
The value of EAMMIN must be set such that in normal operation 80% of all requests to save blocks in the system file SYSEAM can be satisfied without it being necessary to enlarge the file. Experience shows that a size of 4000 allocation units for the initial setting is advisable.
If the value chosen for EAMMIN is too low, this will lead to a higher load on the system due to many dynamic file enlargements and uncontrolled growth of the SYSEAM file.
By choosing suitable values for EAMMIN and EAMSEC or the EAM operand (MINIMAL-SIZE, SECONDARY-ALLOCATION) in /ADD-MASTER-CATALOG-ENTRY und /MODIFY-MASTER-CATALOG-ENTRY, you can keep the variation of the file size of SYSEAM to a minimum or suppress it completely.
It is important to keep the number of required secondary allocations per pubset as low as possible.
EAMSIZ is the maximum value in allocation units within the $TSOS.SYSEAM file that are available to one user alone.
Standard values for the EAM system parameter are heavily dependent on the expected load. The values for EAMMIN and EAMSEC should both be set to a multiple of 8, as this produces optimum adjustment to the internal table structure of EAM.
The value of EAMMEM defines the size of the class 4 memory (in units) used for EAM. It should be a multiple of 8. The pubset-specific definition is implemented using the EAM=*PARAMETERS(VIRTUAL-MEMORY=...) operand in /ADD-MASTER-CATALOG-ENTRY or /MODIFY-MASTER-CATALOG-ENTRY.
This area is created for the home pubset only and is part of the SYSEAM file. First the class 4 memory area is filled, and only once it is full does writing to disk begin (no cache).
Beneficial use (speeding up compilation runs by saving on I/O operations) is only possible if there is sufficient main memory available. Otherwise the benefit of cutting down on physical I/Os on the SYSEAM file will be offset by increased paging of the class 4 memory pages.