Vitess

Vitess is a set of servers and tools meant to facilitate scaling of MySQL databases for the web. It's currently used as a fundamental component of YouTube's MySQL infrastructure.

sougou will be presenting Vitess at Fosdem '14 in the go devroom. Feel free to drop by if you're planning on attending.

• Vision
• Tools
• Concepts
• Getting Started

Features

This is an incomplete list of Vitess features.

Clients

• A Python DBAPI 2.0 compliant client interface.
• A go client interface.
• Simple BSON based protocol with SASL authentication.

vttablet

Smart middleware sitting in front of MySQL and serving clients requests.

• Connection pooling.
• SQL parser: Although very close, the vtocc SQL parser is not SQL-92 compliant. It has left out constructs that are deemed uncommon or OLTP-unfriendly. It should, however, allow most queries used by a well-behaved web application.
• Query rewrite and sanitation (adding limits, avoiding non-deterministic updates).
• Query consolidation: reuse the results of an in-flight query to any subsequent requests that were received while the query was still executing.
• Rowcache: the mysql buffer cache is optimized for range scans over indices and tables. Unfortunately, it’s not good for random access by primary key. The rowcache will instead maintain a row based cache (using memcached as its backend) and keep it consistent by fielding all DMLs that could potentially affect them.
• Update stream: A server that streams the list of rows that are changing in the database, which can be used as a mechanism to continuously export the data to another data store.
• Integrated query killer for queries that take too long to return data.
• Discard idle backend connections to avoid offline db errors.
• Transaction management: Ability to limit the number of concurrent transactions and manage deadlines.

Management

• Cluster configuration is stored using pluggable lock service backends, with the ZooKeeper enabled by default.
• vtctl: command line tool that allows to do most management operations, like initializing a server, changing its type, etc.
• Separate replication and serving graph management.
• vtctld: HTTP daemon giving an overview of the configuration (there's also a JSON API available).
• Fast database snaphsotting and reloading (much faster than mysqldump and LOAD DATA INFILE).

Sharding

• Keyspaces: All tables in a sharded database need to contain a “key” column. Vitess will use these values to decide the target shard for such data. All tables that are indexed by a set of keys are known as a keyspace, which basically represents the logical database that combines all the shards that store them.
• Range based sharding: The main advantage of this scheme is that the shard map is a simple in-memory lookup. The downside of this scheme is that it creates hot-spots for sequentially increasing keys. In such cases, we recommend that the application hash the keys so they distribute more randomly.

Replication

• Split replication: replicate only part of the replication stream basing on provided criteria (useful for vertical or horizontal resharding).

License

Unless otherwise noted, the vitess source files are distributed under the BSD-style license found in the LICENSE file.