Toru Maesaka

Today I was doing some work on writing a small storage engine for Drizzle that we’re hoping will perform good enough to replace the MEMORY/HEAP engine inherited from MySQL. For those that are interested, this engine is going to be based on Tokyo Cabinet’s on-memory b+tree database.

I was a little worried that this task is going to be heavy since I’ve never hacked on a relational database engine before (other than tracing through InnoDB) but it turns out it’s not so bad. I first looked up the engine interface for MySQL then looked at the engines in the Drizzle tree. The interface itself looks very similar but what’s really cool about Drizzle is how the storage engine is registered to the core server with the new plugin system. Here’s a snippet of how this looks with the Blackhole engine:

blackhole_engine= new BlackholeEngine(engine_name);
registry.add(blackhole_engine);

and the de-initialization:

registry.remove(blackhole_engine);
delete blackhole_engine;

If you’re familiar with how a Drizzle plugin is written, you will notice that this is exactly the same; You implement the interface and boom, you register it with the PluginRegistry object. So a storage engine is treated equally just like any other plugin system.

Needless to say, the storage engine declaration is exactly the same as what you would do with any Drizzle plugin:

drizzle_declare_plugin(blackhole)
{
  "BLACKHOLE",
  "1.0",
  "MySQL AB",
  "/dev/null storage engine (anything you write to it disappears)",
  PLUGIN_LICENSE_GPL,
  blackhole_init, /* Plugin Init */
  blackhole_fini, /* Plugin Deinit */
  NULL,           /* status variables */
  NULL,           /* system variables */
  NULL            /* config options */
}
drizzle_declare_plugin_end;

This is nice! a storage engine is just a plugin after all and Drizzle treats it as it ought to be. I will have some more time to hack on this after my memcached webinar so hopefully I’ll have more details posted about the progress on this work soon.

Toru Maesaka drizzle, oss drizzle, engine, plugin, storage