Collection Routing #21

Concepts:

• A collection is a namespace for a KV, Log or Object store
• A collection ID is a sequence of bytes that represent a prefix for all keys in a collection
• A range is a lexicographic partition that holds some range of keys, possibly spanning multiple collections
• A key is an identifier for an element of a collection
• An absolute key is the collection ID + key bytes. If the collection user_posts mapped to \x58\x29 and a request would like to access the key dog plays with cat then the absolute key would be \x58\x29dog\x20plays\x20with\x20cat.

Requests contain:

1. collection+key in the form of user_accounts/alice
2. operation {read, write, CAS, watch, subscribe}

When a server receives a request, it should do one of four things:

• handle it, because the leader of the range containing the absolute key is on the local server
• return a redirect to a known leader of the containing range
• query the meta range for current leader information for the collection if we have not already done so for this collection in a specified rate-limiting period
• return an error communicating that the collection was queried within the rate-limiting period unsuccessfully