Synching Sites

A particular data centre of 40 nodes we have must also send all the data to a secondary, backup site. We use Oracle Coherence's Push Replication pattern to keep these two sites synchronised. How does it do this and how do we write tests for it?

Push Rep uses Coherence*Extend servers which "allows you to access remote Coherence caches using standard Coherence APIs" [1]. It uses TCP to do this, not TCMP (an asynchronous protocol that uses UDP for data transferal) as Coherence normally uses.

Typically, you should "configure Coherence*Extend proxy servers on a dedicated set of machines that server no other purpose. This will allow you to scale your proxy servers independently from the storage-enabled members of the cluster... Coherence*Extend proxy servers are full-blown TCMP members, so they should have fast and reliable communication with the rest of the cluster." [1]

This is not possible nor desirable for our LittleGrid testing since we're just testing functionality. We will, however, need some of the production-like config. On the Extend Server side, we need:

    <caching-schemes>
        <proxy-scheme>
            <service-name>ExtendTcpProxyService</service-name>
            <thread-count>5</thread-count>

            <acceptor-config>
                <tcp-acceptor>
                    <local-address>
                        <address>localhost</address>
                        <port>32199</port>
                    </local-address>
                </tcp-acceptor>

[Note: I reduced the thread count for my test. This value is 50 in production].

On the side of the cluster that is a client of this Extend server (the production site in our case), the config looks like:

   <caching-schemes>
        <remote-invocation-scheme>
            <scheme-name>remote-contingency-invocation</scheme-name>
            <service-name>RemoteContingencyInvocationService</service-name>
            <initiator-config>
                <tcp-initiator>
                    <remote-addresses>
                        <socket-address>
                            <address>localhost</address>
                            <port>32199</port>
                        </socket-address>
                    </remote-addresses>
                    <connect-timeout>30s</connect-timeout>
                </tcp-initiator>

Instead of the usual method of executing code against the data using EntryProcessors, PushRep executes an Invocable against an InvocationService. (Your implementation of Invocable can execute the EntryProcessors you know and love on the remote InvocationService but note that InvocationService.query does not take an affined key as execution of EntryProcessors do).

As for LittleGrid configuration, your primary config will need something like:

        Builder builder = newBuilder()
            .setCacheConfiguration("FILE_WITH_CLIENT_XML_ABOVE")
.
.

and the Extend server config appears to need something like:

            newBuilder().setStorageEnabledExtendProxyCount(1)...

[1] Oracle Coherence 3.5.