Memcached clusters

[berkeli]

Use the set and get commands again to understand the behaviour of this mcrouter configuration. How does the behaviour differ from the replicated cluster?

1. In the case of replicated cluster we can get it from each memcached instance, all of the commands below return the same value since data is replicated:

• printf "get mykey\r\n" | nc localhost 11211 - this is the router, returns data
• printf "get mykey\r\n" | nc localhost 11212 - replica, returns same data
• printf "get mykey\r\n" | nc localhost 11213 - replica, returns same data
• printf "get mykey\r\n" | nc localhost 11214 - replica, returns same data

1. In the case of sharded cluster we can can only get the data from the router or from the instance that stores the data, in my case:

• printf "get mykey\r\n" | nc localhost 11211 - this is the router, returns data
• printf "get mykey\r\n" | nc localhost 11212 - returns data, as the router stored it in this instance
• printf "get mykey\r\n" | nc localhost 11213 - doesn't return data
• printf "get mykey\r\n" | nc localhost 11214 - doesn't return data

[sre-is-laura]

yep, the cache topology tester looks right to me. good work

[illicitonion]

This looks great! Left a couple of very minor thoughts on naming :)

[illicitonion]

A common pattern I've seen naming-wise is to name the interface CacheService, to have the standard/obvious implementation be private and called cacheService, and to have NewCacheService return a CacheService (i.e. the interface). This means that you don't need the ugly I-prefix, and that the caller can only access the publicly declared interface functionality rather than relying on internal implementation details.

[illicitonion]

From the name checkIfSharded, I would expect this to probably return a boolean, and it's not super clear what "not sharded" (i.e. false) would mean.

I'd maybe call this checkMode (to imply "there are multiple modes it may return") or detectShardedOrReplicated (to be clear what the universe of return values is).