This Windows only embedded engine has long been part of Microsoft Exchange and Active Directory servers. The API was public but not well documented. Berkeley DB was a quality cross-platform alternative but I suspect that some permutation of RocksDB now dominates this use case.
It should be noted that local SQL Server using fast IPC communication is quite good and rumors of Microsoft Exchange replacing ESE with SQL Server have popped up many times over the years.
I thought this was the Jet of MS Access but they call that JET Red.
From the ESE wiki page:
> For JET Red storage engine of Microsoft Access, see Microsoft Jet Database Engine.
> Extensible Storage Engine (ESE), also known as JET Blue, is an ISAM (indexed sequential access method) data storage technology from Microsoft. ESE is the core of Microsoft Exchange Server, Active Directory, and Windows Search. It's also used by a number of Windows components including Windows Update client and Help and Support Center. Its purpose is to allow applications to store and retrieve data via indexed and sequential access.
> ESE provides 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. Transactions in ESE are highly concurrent making ESE suitable for server applications. ESE caches data intelligently to ensure high performance access to data. In addition, ESE is lightweight making it suitable for auxiliary applications.
> The ESE Runtime (ESENT.DLL) has shipped in every Windows release since Windows 2000 [...]
I was wondering how that might fare with the SQL Server edition meant to be bundled with apps. Besides being non-SQL seems it could be lighter keeping transactions and concurrency.
It should be noted that local SQL Server using fast IPC communication is quite good and rumors of Microsoft Exchange replacing ESE with SQL Server have popped up many times over the years.