[dgnorton]

Member of the engineering team here - I would break the history into 3 phases:

1) Alpha / Beta phase where we experimented with several off-the-shelf key-value stores (RocksDB, LevelDB, & BoltDB). During this early phase, we learned from observing a wide variety of workloads / use-cases that we needed a custom built engine to achieve our early performance goals. But, using these off-the-shelf key-value stores allowed our (at the time) very small team to focus on developing a useful beta product and gathering user feedback.

2) TSM storage engine for 1.0 - Developed from scratch based on our learnings from phase 1, this was the first production storage engine that shipped with 1.0 in 2016 and carried us through 2.0. It served as the workhorse for 3 - 4 years as both the number of users and size of their workloads skyrocketed, eventually bumping into architectural limits of TSM.

3) IOx - equipped with a larger engineering team and years of experience with a wide variety of workloads and use-cases, IOx was developed to handle rapidly growing time series workloads that users need to handle.