Friday, February 16, 2018

Sharded replica sets - MySQL and MongoDB

MongoDB used to have a great story for sharded replica sets. But the storage engine, sharding and replica management code had significant room for improvement. Over the last few releases they made remarkable progress on that and the code is starting to match the story. I continue to be impressed by the rate at which they paid off their tech debt and transactions coming to MongoDB 4.0 is one more example.

It is time for us to do the same in the MySQL community.

I used to be skeptical about the market for sharded replica sets with MySQL. This is popular with the web-scale crowd but that is a small market. Today I am less skeptical and assume the market extends far beyond web-scale. This can be true even if the market for replicasets, without sharding, is so much larger.

The market for replica sets is huge. For most users, if you need one instance of MySQL then you also need HA and disaster recovery. So you must manage failover and for a long time (before crash-proof slaves and GTID) that was a lousy experience. It is better today thanks to cloud providers and DIY solutions even if some assembly is required. Upstream is finally putting a solution together with MySQL Group Replication and other pieces.

But sharded replica sets are much harder, and even more so if you want to do cross-shard queries and transactions. While there have been many attempts at sharding solutions for the MySQL community, it is difficult to provide something that works across customers. Fortunately Vitess has shown this can be done and already has many customers in production.

ProxySQL and Orchestrator might also be vital pieces of this stack. I am curious to see how the traditional vendors (MySQL, MariaDB, Percona) respond to this progress.


I think binlog server should be part of the solution. But for that to happen we need a GPLv2 binlog server and that has yet to be published.