Adam Wiggins, Heroku
Heroku: run, maintain, and scale your RoR apps. Leave sysadmin over to someone else.
Home to 40,000 applications
Benefit of being able to see a large number of applications go from tiny to huge. (Most of us get to see one or two of these.)
Automatically scaling apps -- without code changes.
Cloud is about horizontal scalability
Take advantake of cloud: shardable resources
Making the resources upon which the apps rely horizontally scalable ==> scalable apps.
Father of all modern shardable resources: memcached ("hash table in the sky")
Facebook: 800 memcached servers w/28 TB of memory. These appear as one big hashtable.
Is memcached cheating?
Look at other areas: CouchDB
Shardable: clients can go to any server
Share nothing: nodes communicate only when asked to replicate, not all the time. And they only need to be in contact with one other node.
ORA book coming on CouchDB: http://books.couchdb.org/relax
Big data processing; cut data into small chunks; cut big work into distributable jobs.
Like memcached with persistence; shards with hashring; lists and sets; extremely fast and lightweight. (You use the memcached client, too.)
Like Squid, but horizontally scalable; share-nothing, does not
share cache database; combine with
ngx_http_upstream_consistent_hash for hashring-style access --
lessons from memcached.
Queueing jobs; broadcasting to cluster via exchanges; cross-language. AMQP implementation.
(doesn't fit the pattern like the others)
Principles discussed above come out of the functional programming world; share-nothing, high concurrency, no mutable variables, lightweight processes.
Q from stilkov: you support RDBMS in heroku apps, how does that work? A We do support it, but all the recovery strategies we have for the other applications don't work. There is no magic for that. You have to fundamentally rethink how you architect a database to scale.
Q how easy is it to backup CouchDB? A Trivially easy. Since it backs up by HTTP, you can use all the same infrastructure. You basically post to _replicate (or something), and it just works. Replication capabilities are amazing.
Q downsides of document DB? A ad-hoc queries; SQL engines have been evolving for decades to be really fast and efficient. With CouchDB you need to define a view up front so it'll create an index. This is great for webapps because you know this, but not for discovery queries.