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MongoDB Specifications

This repository holds in progress and completed specification for features of MongoDB, Drivers, and associated products. Also contained is a rudimentary system for producing these documents.

Driver Mantras

When developing specifications -- and the drivers themselves -- we follow the following principles:

Strive to be idiomatic, but favor consistency ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

Drivers attempt to provide the easiest way to work with MongoDB in a given language ecosystem, while specifications attempt to provide a consistent behavior and experience across all languages. Drivers should strive to be as idiomatic as possible while meeting the specification and staying true to the original intent.

No Knobs ~~~~~~~~

Too many choices stress out users. Whenever possible, we aim to minimize the number of configuration options exposed to users. In particular, if a typical user would have no idea how to choose a correct value, we pick a good default instead of adding a knob.

Topology agnostic ~~~~~~~~~~~~~~~~~

Users test and deploy against different topologies or might scale up from replica sets to sharded clusters. Applications should never need to use the driver differently based on topology type.

Where possible, depend on server to return errors ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

The features available to users depend on a server's version, topology, storage engine and configuration. So that drivers don't need to code and test all possible variations, and to maximize forward compatibility, always let users attempt operations and let the server error when it can't comply. Exceptions should be rare: for cases where the server might not error and correctness is at stake.

Minimize administrative helpers ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

Administrative helpers are methods for admin tasks, like user creation. These are rarely used and have maintenance costs as the server changes the administrative API. Don't create administrative helpers; let users rely on "RunCommand" for administrative commands.

Check wire version, not server version ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

When determining server capabilities within the driver, rely only on the maxWireVersion in the hello response, not on the X.Y.Z server version. An exception is testing server development releases, as the server bumps wire version early and then continues to add features until the GA.

When in doubt, use "MUST" not "SHOULD" in specs ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

Specs guide our work. While there are occasionally valid technical reasons for drivers to differ in their behavior, avoid encouraging it with a wishy-washy "SHOULD" instead of a more assertive "MUST".

Defy augury ~~~~~~~~~~~

While we have some idea of what the server will do in the future, don't design features with those expectations in mind. Design and implement based on what is expected in the next release.

Case Study: In designing OP_MSG, we held off on designing support for Document Sequences in Replies in drivers until the server would support it. We subsequently decided not to implement that feature in the server.

The best way to see what the server does is to test it ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

For any unusual case, relying on documentation or anecdote to anticipate the server's behavior in different versions/topologies/etc. is error-prone. The best way to check the server's behavior is to use a driver or the shell and test it directly.

Drivers follow semantic versioning ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

Drivers should follow X.Y.Z versioning, where breaking API changes require a bump to X. See 
_ for more.

Writing Documents

Write documents using

, following the
Documentation Style Guidelines 

Store all source documents in the


.. _


Prose test numbering

When numbering prose tests, always use relative numbered bullets (

). New tests must be appended at the end of the test list, since drivers may refer to existing tests by number.

Outdated tests must not be removed completely, but may be marked as such (e.g. by striking through or replacing the entire test with a note (e.g. Removed).

Building Documents

To build documents issue the

command in a local copy of this repository. The output PDFs end up in the
directory. The build depends on:
  • Python Docutils 
  • A functioning basic LaTeX/TeX install with

    . If you run OS X, use

make all
will build all documents in the
folder. The system builds all targets in


make setup
to generate (or regenerate) a
file which provides specific targets for all files in the source file so you can choose to compile only some of the files that you need. Once generated, running "
make [file-name-without-extension]
" will rebuild only those files (if needed.)


make clean
to remove the
directory and "
" to remove the LaTeX by-products from

.. _


Converting to JSON

There are many YAML to JSON converters. There are even several converters called

in NPM. Alas, we are not using
anymore, but instead the
_ package. Use only that converter, so that JSON is formatted consistently.


npm install -g js-yaml
, then run
in the
directory at the top level of this repository to convert all YAML test files to JSON.


All the specs in this repository are available under the

Creative Commons Attribution-NonCommercial-ShareAlike 3.0 United States License 

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