[infinispan-dev] Shipping logical address String in Hot Rod protocol v1.1?

[Galder Zamarreño]

Hi,

We've been having a discussion this morning with regards to the Hot Rod changes introduced in 5.1 with regards to hashing.

When Hot Rod server is deployed in AS, in order to start correctly, it requires the Hot Rod server to start before any other (clustered) caches in AS. This is because any hashing can only be done once the hash has been calculated on the hot rod endpoint.

Although this can be fixed in a hacky way (have all caches configured to start lazily and let the Hot Rod server start the topology cache and then all defined caches, ugh), we're considering a slight change to Hot Rod protocol v 1.1 (https://docs.jboss.org/author/display/ISPN/Hot+Rod+Protocol+-+Version+1.1) that would solve this problem.

Instead of hashing on the hot rod endpoint address (host:port), we could hash on JGroups's Address UTF-8 toString representation, which is the logical address. The advantage here is any cache can calculate the hash on this from the start, no need to wait for Hot Rod server to start. The downside is that Hot Rod clients need to be aware of this UTF-8 string in order to hash to the same thing, so it'd mean shipping this back to the clients alongside the hot rod endpoint info.

In spite of the added bytes, there's a benefit to this, and that is the fact that we're not tying a specific format to the String. That is, we're just telling the clients to take this UTF-8 string and hash on that. So, it's internal representation could evolve over time with no impact to the client. In the current v 1.1 protocol, clients and servers assume a String of format host:port to do the hashing.

A third way to fix this would have been to have Hot Rod servers run with a different cache manager to the rest (but still same JGroups channel), but according to Dan, AS7 is not capable of doing this.

So, what does people think of this protocol change in v1.1? This version was introduced in 5.1 and since we still have not released yet, this is the right time to consider protocol changes like this. Personally, I'm in favour.

Cheers,
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Galder Zamarreño
Sr. Software Engineer
Infinispan, JBoss Cache