☜	OMI - Replication Draft MDC Standard					☞

4.6 Replication

Implementers of OMI may offer replication of changes to selected global variables. That is, set and kill operations are also applied to global variables of the same name in 1 or more other environments, some of which may reside on other OMI nodes.

Replication is often applied symmetrically to keep the databases identical, whichever one a client changes explicitly. For example, ^XX on computer A is replicated to ^XX on computer B and vice versa, so a change to either one evokes an OMI request to change the other. Then the protocol must avoid an endless series of transactions caused by mutual replication.

Requests (set, set extract, set piece, and kill) that alter variables shall include a replication flag to indicate whether the request should be replicated.

NOTE – Implementations of OMI are not required to perform replication. They are required to provide the replication flag in order to cooperate with implementations that do perform replication.

All agents shall originate set, set extract, set piece, and kill requests with replication enabled. Servers shall attempt the requested operation whether or not replication is enabled, subject to other considerations like authorization, and shall reply as described in 4.3.3.

An implementation that supports replication shall take further action if and only if it successfully performs a set, set extract, set piece, or kill operation with replication enabled. (The operation may have originated from an OMI request or from a local set, set extract, set piece, or kill by a process on the server’s own node.) The agent on that node shall:

• establish sessions with the replication destination nodes, if not already established.
• send the same request with replication disabled to each of the destinations, in effect saying, "This is a replication request. Do not replicate it further."

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Copyright © Examples: 1995-2024 Ed de Moel;
Copyright © Annotations: 2003-2008 Jacquard Systems Research
Copyright © Annotations: 2008-2024 Ed de Moel.

Some specifications are "approved for inclusion in a future standard". Note that the MUMPS Development Committee cannot guarantee that such future standards will indeed be published.

This page most recently updated on 14-Nov-2023, 22:14:56.

For comments, contact Ed de Moel (demoel@jacquardsystems.com)