Shares
In active mode, WLM reads a configuration file that assigns each class shares of the system resources. The class gets its resource in proportion of its share to the total. For example, assume there are two classes:
WebSphere 300Tape Backup 150The WebSphere class would get 300/(300+150) = 66.7% of the resource, and Tape Backup would get 33.3%. If later another application, Billing, was also assigned 150 shares, the split becomes WebSphere 300/(300+150+150) = 50%, Tape Backup and Billing = 25%.
Shares are not percentages; they are relative amounts of the resource. In the preceding example, if the resource was processor, and the LPAR had three processors, the first shares would be WebSphere 200% and Tape Backup 100% of a processor. These correspond, not to dedicated processors, but to the total processor time allocated across all three. If later a fourth processor was added before the Billing application, the shares increase to WebSphere 266.7%, Tape Backup 133.3%.
Subclasses also have shares, but in this case they refer to the superclass's resource, not the total resource. So assume the first example was as follows:
WebSphere.Mortgages 200WebSphere.Account Opening 300Mortgages would get 200/(200+300) = 40% of 66.7% = 26.7% of the processor resource, and Account Opening would get 40%. With three processors, that would be 80% and 120% of a processor, respectively.
These shares are not limits; processes can use more than their fair share if no other applications want them. But where there is contention, the available resource is given first to processes below their fair share. Further, if a class has no active processes, it is completely ignored in the calculation. Assume an example with:
WebSphere 300Tape Backup 150Billing 150If Tape Backup were inactive, WebSphere would get 66.7% and Billing would get 33.3% of the available resource. WLM also supports limits, rather than shares (which are discussed in Shares).