This comes from the HOST_NAME field in the LSB_EVENTS_EXECHOSTLIST table . If this is null, then set this field to "-". Also if it contains a list of host, we'll only use the first one for this field.
Once we get the host name, we then look it up in the wi_hostcode table to see if we have already has a record of it in there. If we do, then we'll get the code back, otherwise, we will insert it into the wi_hostcode table and generate the code. The code itself is a positive integer and each new code is equal to the maximum of the existing sequence number +1. If it is null, then the "Subhost_Code" field will be used.