IBM z13s Technical Manual page 135

A zIIP runs only IBM authorized code. This IBM authorized code includes the z/OS JVM in
association with parts of system code, such as the z/OS dispatcher and supervisor services.
A zIIP cannot process I/O or clock comparator interruptions, and it does not support operator
controls, such as IPL.
Java application code can either run on a CP or a zIIP. The installation can manage the use of
CPs so that Java application code runs only on CPs, only on zIIPs, or on both.
Two execution options for zIIP-eligible code execution are available. These options are
user-specified in IEAOPTxx, and can be dynamically altered by the SET OPT command. The
following options are currently supported for z/OS V1R10 and later releases:
Option 1: Java dispatching by priority (IIPHONORPRIORITY=YES): This is the default
option, and specifies that CPs must not automatically consider zIIP-eligible work for
dispatching on them. The zIIP-eligible work is dispatched on the zIIP engines until WLM
determines that the zIIPs are overcommitted. WLM then requests help from the CPs.
When help is requested, the CPs consider dispatching zIIP-eligible work on the CPs
themselves based on the dispatching priority relative to other workloads. When the zIIP
engines are no longer overcommitted, the CPs stop considering zIIP-eligible work for
dispatch.
This option runs as much zIIP-eligible work on zIIPs as possible, and allows it to spill over
onto the CPs only when the zIIPs are overcommitted.
Option 2: Java dispatching by priority (IIPHONORPRIORITY=NO): zIIP-eligible work runs
on zIIPs only while at least one zIIP engine is online. zIIP-eligible work is not normally
dispatched on a CP, even if the zIIPs are overcommitted and CPs are unused. The
exception is that zIIP-eligible work can sometimes run on a CP to resolve resource
conflicts.
Therefore, zIIP-eligible work does not affect the CP utilization that is used for reporting
through the subcapacity reporting tool (SCRT), no matter how busy the zIIPs are.
If zIIPs are defined to the LPAR but are not online, the zIIP-eligible work units are processed
by CPs in order of priority. The system ignores the IIPHONORPRIORITY parameter in this
case and handles the work as though it had no eligibility to zIIPs.
zIIPs provide the following benefits:
Potential cost savings.
Simplification of infrastructure as a result of the collocation and integration of new
applications with their associated database systems and transaction middleware, such as
DB2, IMS, or CICS. Simplification can happen, for example, by introducing a uniform
security environment, and by reducing the number of TCP/IP programming stacks and
system interconnect links.
Prevention of processing latencies that occur if Java application servers and their
database servers are deployed on separate server platforms.
.The following DB2 UDB for z/OS V8 or later workloads are eligible to run in SRB mode:
Query processing of network-connected applications that access the DB2 database over
a TCP/IP connection by using IBM Distributed Relational Database Architecture (DRDA).
DRDA enables relational data to be distributed among multiple systems. It is native to DB2
for z/OS, and so reduces the need for more gateway products that can affect performance
and availability. The application uses the DRDA requester or server to access a remote
database. IBM DB2 Connect™ is an example of a DRDA application requester.
Star schema query processing, mostly used in business intelligence (BI) work. A
schema
is a relational database schema for representing multidimensional data. It stores
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