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Distributed and persistent key-value database

Features

• Built on Tokyo Tyrant. One of the fastest key-value databases [benchmark]. Tokyo Tyrant has been in development for many years and is used in production by Plurk.com, mixi.jp and scribd.com (to name a few)...
• Great performance (comparable to memcached!)
• Can store millions of keys on very few servers - tested in production
• Scale out by just adding nodes
• Nodes are replicated via master-master replication. Automatic failover and load balancing is supported from the start
• Ability to script and extend using Lua. Included extensions are incr and a fixed list
• Hot backups and restore: Take backups and restore servers without shutting them down
• LightCloud manager can control nodes, take backups and give you a status on how your nodes are doing
• Very small foot print (lightcloud client is around ~500 lines and manager about ~400)
• Python only, but LightCloud should be easy to port to other languages.
• Ruby port under development!

But that's not all, we also support Redis (as an alternative to Tokyo Tyrant)!:

• Check benchmarks and more details about Redis in LightCloud adds support for Redis.

Stability

It's production ready and Plurk.com is using it to store millions of keys on only two servers that run 3 lookup nodes and 6 storage nodes (these servers also run MySQL).

How LightCloud differs from memcached and MySQL?

memcached is used for caching, meaning that after some time items saved to memcached are deleted. LightCloud is persistent, meaning that once you save an item, it will be there forever (or until you delete/update it).

MySQL and other relational databases are not efficient for storing key-value pairs, a key-value database like LightCloud is.

The bottom line is that LightCloud is not a replacement for memcached or MySQL - it's a complement that can be used in situations where your data does not fit that well into the relational model.

How LightCloud differs from redis and memcachedb?

LightCloud is a distributed and horizontal scaleable database. memcachedb or redis aren't. This is pretty crucial to understand and we can read that many have not really understood this.

Basically, LightCloud could be built on top of memcachedb or redis - where the nodes would be memcachedb or redis instead of Tokyo Tyrant. The reason why Tokyo Tyrant was chosen is because it's the fastest key-value database around with the ability to do 1 million SETs and GETs under 1 second (see benchmark).

Benchmark against memcached

Please do note that comparing to memcached is unfair as memcached is memory only - LightCloud has to hit the disk. That said, here is what it takes to do 10.000 gets and sets:

Elapsed for 10000 gets: 1.74538516998 seconds [memcache]
Elapsed for 10000 gets: 3.57339096069 seconds [lightcloud]

Elapsed for 10000 sets: 1.88236999512 seconds [memcache]
Elapsed for 10000 sets: 9.23674893379 seconds [lightcloud]

Benchmark program

If things were done in batches and time wasn't spent in Python and network layer, then Tokyo Tyrant would be able to perform much better. From the official Tokyo Cabinet benchmark you can see following stats:

• 1 million GETS in < 0.5 seconds
• 1 million SETS in < 0.5 seconds

These updates are not that realistic in practice.

Useful links

Some useful links to LightCloud related sites:

• Plurk Open Source Trac
• Hacker news discussion

Also do subscribe to LightCloud's mailing list:

Lua extension

Like stated above you can script LightCloud nodes via Tokyo Tyrant's Lua extension support. This basically means that you can create your own extensions in a very easy manner (the speed is comparable to C).

Here is how you extend with a incr command:

function incr(key, value)
   value = tonumber(value)
   if not value then
      return nil
   end
   local old = tonumber(_get(key))
   if old then
      value = value + old
   end
   if not _put(key, value) then
      return nil
   end
   return value
end

And for something a bit more crazy:

• Inverted index by the Lua extension of Tokyo Tyrant

License

LightCloud is copyrighted by Plurk Inc and is licensed under the BSD license.

LightCloud development is lead by amix.