In TXSeries environment, a transaction runs in a cicsas process. The number of ungrouped transactions (Transactions where TClass is None) that can be run in parallel in a TXSeries region is controlled by the MaxServer attribute in Region Definition(RD) Stanza. The number of application servers available for taking new transaction work at any point in time is controlled by the MinServer attribute in RD Stanza.
CST3 transaction can be used to monitor and understand the application server specific runtime load on the system. "Times AppServs Full" attributes in CST3 screen gives information on number of times the region reached the MaxServer attribute set in the Region definition to execute the transactions. If you see the "Times AppServs Full" value to be high,then you can consider increasing the number of CICSAS process running in the region with
CEMT SET SYSTEM MAXServer(MAX_server_count) MInserver(MIN_server_count)
MAX_server_count value is the maximum number of processes that TXSeries region uses to process transactions and MIN_server_count value is the minimum number of processes that TXSeries region uses to process transactions. At any time, the number of transactions that can start immediately depends on the MIN_server_count value. If the number of transactions processed crosses the cicsas readily available, a new CICSAS process will start to process the new request until the total number of CICSAS process reaches the MAX_server_count value.
MaxServer can be reduced by reviewing the statistics file's "Peak Number Tasks" over a period of time.