Understanding Implementing Primary-Secondary Dispatchers
Primary-Secondary dispatching is where a master domain allocates messages to one or more secondary dispatchers for processing. This section provides an overview of primary-secondary dispatcher processing.
Primary-Secondary Dispatcher Processing
A secondary dispatcher processes service operations assigned to it by a primary dispatcher.
A primary domain allocates service operations to a secondary for processing when:
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The primary detects that a secondary dispatcher is active and not busy processing service operations.
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The secondary has an active queue on which the primary is currently processing service operations.
The dispatcher(s) processing in secondary mode then process the allocated service operations.
Primary and secondary dispatchers can reside on the same or on different machines.
Note:
When primary-secondary processing is implemented, there can be only one primary domain at a given time.
You can create a domain consisting of only dedicated secondary pub/sub servers. These servers register themselves as secondaries, along with additional configurable information, such as the number of process handlers booted, so that the appropriate primary server can use that information to allocate work (service operations to process) to the secondary server(s).
The primary domain can allocate work to one or more secondary domains.
Secondary Types
There are two types of dispatcher secondaries:
| Term | Definition |
|---|---|
|
Dynamic secondaries |
A dynamic secondary can change from a primary to a secondary. Dynamic secondaries are configured in conjunction with domain failover. If a secondary domain has the highest priority within a failover group, it can dynamically change to a primary during failover. You configure dynamic secondaries in the Failover Configuration page in the Service Operations Monitor. |
|
Static secondaries |
Static secondaries are those that cannot become primaries without manual configuration. You configure static secondary domains in PSADMIN. |
|
Template secondaries |
A template secondary is an already-configured primary domain that you import into PSADMIN an save as a secondary domain. Template secondaries enable you to dynamically add secondary domains without performing any configuration changes in PSADMIN. You use the Import Domain Configuration command in PSADMIN to import a primary domain configuration and then save it as a static secondary domain. The secondary domain created uses all the Pub/Sub processes and queue lists configured for the primary domain on which the secondary template is based. If dedicated servers are configured for the primary domain, they are also imported an available on the secondary domain. |
Failover and Primary-Secondary Dispatchers
You can create a secondary domain for use in domain failover.
The domain with the highest priority dynamically becomes the active domain (primary domain) in each group during failover. The next domain in priority will be programmatically configured as an active secondary domain.
When a failover occurs the domain that failed becomes inactive. The failover domain specified goes from an active secondary to an active primary. The next domain in priority then becomes an active secondary.
You can set failover for secondary dispatchers. However, secondary dispatchers cannot be part of any group and you cannot prioritize them.