> For the complete documentation index, see [llms.txt](https://help.iviva.com/lucy/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://help.iviva.com/lucy/my-work-folders/databases/understanding-databases.md).

# Understanding Databases

A more technical understanding of how databases work

Internally, Lucy uses `MongoDB` (or a MongoDB-compatible service) as its storage engine for collections. Consequently, many standard MongoDB semantics apply to databases.

This includes:

* Every document has a `_id` field that is generated automatically.
* The ability to run custom MongoDB-compatible queries on your database.