The memcache protocol has an INCR command, which atomically increments a stored value. MySQL Cluster is able to take simple operations (like incrementing a counter) and "push them down" to run on a data node with a lock held. Acquire the lock, increment the value, read it, and release the lock.
Originally in memcached, the incrementing sequence number was local to one memcache server, and was also volatile. Whenever the memcached server restarted, the sequence would be reset. Today, though, we can put cluster and memcached together, and instead of a volatile local sequence number, we get a durable and shared one.
This is a very simple application. Keep reading to see the whole thing, start to finish. In my example I'll use MySQL Cluster 7.2.4 and the memcached ASCII protocol. There is a minor (but annoying) bug, already fixed in 7.2.6, that prevented this from working with the binary protocol. So, keep that in mind, and grab 7.2.6 or later once it is released.
Continue reading "A Sequence Generator"
PlanetMySQL Voting: Vote UP / Vote DOWN
Originally in memcached, the incrementing sequence number was local to one memcache server, and was also volatile. Whenever the memcached server restarted, the sequence would be reset. Today, though, we can put cluster and memcached together, and instead of a volatile local sequence number, we get a durable and shared one.
This is a very simple application. Keep reading to see the whole thing, start to finish. In my example I'll use MySQL Cluster 7.2.4 and the memcached ASCII protocol. There is a minor (but annoying) bug, already fixed in 7.2.6, that prevented this from working with the binary protocol. So, keep that in mind, and grab 7.2.6 or later once it is released.
Continue reading "A Sequence Generator"
PlanetMySQL Voting: Vote UP / Vote DOWN