Microsoft’s Extensible Storage Engine (ESE), an advanced indexed and sequential access method (ISAM) storage technology, is now open source.

First shipping in Windows NT 3.51 and shortly thereafter in Exchange 4.0, and rewritten twice in the 90s, and heavily updated over the subsequent two decades after that, ESE aka JET Blue remains a core Microsoft asset to this day.

ESE enables applications to store and retrieve data from tables using indexed or sequential cursor navigation. It supports denormalized schemas including wide tables with numerous sparse columns, multi-valued columns, and sparse and rich indexes. It enables applications to enjoy a consistent data state using transacted data update and retrieval.

A crash recovery mechanism is provided so that data consistency is maintained even in the event of a system crash.

Moreover, it provides ACID (Atomic Consistent Isolated Durable) transactions over data and schema by way of a write-ahead log and a snapshot isolation model. Transactions in ESE are highly concurrent, making ESE useful for server applications.

It caches data to maximize high performance access to data. In addition, it is lightweight, making it useful for applications that serve in auxiliary roles.

The source code for Microsoft’s Extensible Storage Engine is now available on GitHub.