Coherence extend Proxy service with no storage.

Question

Hi
I am implementing coherence where I have the requirement as follows.
1. Create two Coherence Servers in Weblogic console. These are cache stores using replicated cache scheme.
2. Create tow Coherence servers which acts as proxy. These should not contain any cache.
Can some body tell me how to create the cache config for the step2 i.e proxy servers? when I created the proxy server without giving the cache names I am getting cache not found error.

Answer 1

Hi Sri,
There are various options available for this but...
If I was building this application I would probably make your Web Cluster storage-disabled members of the Coherence cluster (assuming they are Java). This will give them quicker access to data than using Extend. You would then not need the proxy servers. I would use distributed caches in your Coherence storage nodes rather than replicated and then configure near-caches in your Web layer. If you wanted to you could use the resource from the servers that you were using for proxy servers as storage nodes as this would give you a little more capacity and make the cluster a little mode durable - i.e. less prone to complete failure if you lost a node.
So, your coherence-cachestore-config file would look like this
<cache-config xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
        xmlns="http://xmlns.oracle.com/coherence/coherence-cache-config"
        xsi:schemaLocation="http://xmlns.oracle.com/coherence/coherence-cache-config coherence-cache-config.xsd">
    <defaults>
        <serializer>pof</serializer>
    </defaults>
    <caching-scheme-mapping>
        <cache-mapping>
            <cache-name>products</cache-name>
            <scheme-name>distributed-scheme</scheme-name>
        </cache-mapping>
    </caching-scheme-mapping>
    <caching-schemes>
        <distributed-scheme>
            <scheme-name>distributed-scheme</scheme-name>
            <service-name>DistributedCacheScheme</service-name>
            <backing-map-scheme>
                <local-scheme/>
            </backing-map-scheme>
            <autostart>true</autostart>
        </distributed-scheme>
    </caching-schemes>
</cache-config>The cache configuration for the Web layer would be similar but have near caching
<cache-config xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
        xmlns="http://xmlns.oracle.com/coherence/coherence-cache-config"
        xsi:schemaLocation="http://xmlns.oracle.com/coherence/coherence-cache-config coherence-cache-config.xsd">
    <defaults>
        <serializer>pof</serializer>
    </defaults>
    <caching-scheme-mapping>
        <cache-mapping>
            <cache-name>products</cache-name>
            <scheme-name>near-scheme</scheme-name>
        </cache-mapping>
    </caching-scheme-mapping>
    <caching-schemes>
        <near-scheme>
            <scheme-name>near-scheme</scheme-name>
            <front-scheme>
                <local-scheme>
                    <high-units>1000</high-units>
                </local-scheme>
            </front-scheme>
            <back-scheme>
                <scheme-ref>distributed-scheme</scheme-ref>
            </back-scheme>
        </near-scheme>
        <distributed-scheme>
            <scheme-name>distributed-scheme</scheme-name>
            <service-name>DistributedCacheScheme</service-name>
            <backing-map-scheme>
                <local-scheme/>
            </backing-map-scheme>
            <autostart>true</autostart>
        </distributed-scheme>
    </caching-schemes>
</cache-config>The above near cache would only hold 1000 entries, and Coherence will manage expiry of this. You could tune this figure, other other expiry setting to optimize the data access for your Web layer - as described in the near cache docs here http://docs.oracle.com/cd/E24290_01/coh.371/e22837/cache_config.htm#BABGFCII Storage disbaled nodes with near caches are not always the best approach, but given you are using them in a long-live Web layer and the data does not change very often, I think they would be good for you to use.
As I said though, as with a lot of things in Coherence, there are a number of options available to you, some good, some not so good; the above option is just the one I would choose. Given the requirements you have mentioned there is actually not much wrong with the solution you have chosen apart from access to data is slower as there are always two network hops involved with the proxy in the middle and it would not scale up so well if you wanted to grow the system.
JK