Distributed Name Service (DNS) Management Operations Manual

DNS Database Replication
How DNS Exports the Name Database
31258 Tandem Computers Incorporated 5–3
The Queue File The queue file assists the communication between the name manager and name
exporter. The queue file is composed of four logical files: the primary queue,
secondary queue, hold queue, and export control file.
The primary queue serves as a place for the name manager to store export requests
until acted upon by the name exporter. In addition to providing a safe storage place,
the primary queue acts as a buffering mechanism between the name manager and the
name exporter. The buffering allows export requests to be generated by the name
manager at a rate that is independent of the rate at which the name exporter is able to
process them.
The queue file can contain one secondary queue for each remote system in the Expand
network. Each secondary queue holds requests destined for a single remote system.
The queue file can contain one hold queue for each remote system in the Expand
network. Each hold queue holds requests that could not be exported to a node
because of type-name incompatibilities.
The export-control file portion of the queue file contains control information.
DNS Database
Replication
An application or an operator using DNSCOM issues the ADD command to add a
name, the ALTER command to update a name, or the DELETE command to remove a
name. The request goes to the DNS name manager, which updates the definition
locally. If appropriate, the DNS name manager then queues a request for the DNS
name exporter, which sends the new definition or update to another node.
The DNS name manager on the other node can update its definition, but only upon
request of the DNS name exporter on the definition node. If a node in the domain of a
definition is unavailable, the DNS name exporter sends the information when the
destination node becomes available again. (In the meantime, the name exporter can
handle other requests.)
The following subsections explain in greater detail how DNS databases are exported.
The Export Process As the name manager processes an ADD, ALTER, or DELETE command involving a
replicated name definition, it inserts export requests into the primary queue. Since the
queue file is a TMF-audited file, the write to the primary queue is done under the same
TMF transaction as the database update. If that transaction is subsequently aborted,
the export request in the primary queue is deleted during TMF transaction backout.