With this module you can store serde serializable types in simple newline delimited json formatted text files and index fields in those records for quick querying and retreival of matching records not unlike in a relational database.
The main intended use case is logging of important books and records that need to be stored in a simple and accessible format which can be processed by external tools and backed up online by simple tools. Writing such records as json text to simple text files is about as interoperable and resiliant as you can get. At the same time this library will build an index of an arbitrary set of fields in your records so that queries can be run on the data set as if it was in a database. The index can be freely deleted, and if it becomes corrupted, it can simply be rebuilt, the core data is never touched.
This is not exactly a full database, since it doesn't support modification of records efficiently. If you want to change an existing record, you can just do that, you can even open the file in emacs and just edit it. However in that case the entire index will be invalidated and rebuilt, which can take some time. Therefore this should be considered an append only database, since only append is implemented efficiently (which for our use case is perfectly fine).