Ever wonder what would happen to an open source database project in case its main developers “got hit by a bus”? Or, less dramatically, if they leave the project completely. That’s what the “bus factor” (also called “truck factor”) measures: how many people would have to disappear before no one left knows how to fix or update specific parts of the code.

The Bus Factor Ranking

I’ve been messing around with a tool called the Bus Factor Explorer by JetBrains to explore the associated risk in some of the most popular open source databases. I looked at six of the big ones to see where they stand. Here’s the current baseline (March 2026) according to this tool:

Database

Bus Factor (higher is better)

MongoDB

7

MariaDB

5

Redis

5

MySQL

2

PostgreSQL

2

SQLite

2

For example, for MongoDB to “hit a wall”, 7 devs would have to leave the project. For MySQL, PostgreSQL, and SQLite, if 2 devs leave, the project is at risk of stalling. Of course, this is just one factor; there are other factors that influence the continuation of open source projects, but this is still an interesting insight you can take into consideration when choosing a database.

The tool has a categorization according to the project’s bus factor (a baseline that can be adjusted in the tool if you want):

Simulating Top Contributors Leaving the Projects

I also used the tool to see what happens to the root directories (the functional parts of the code) if you start unchecking the top contributors to each project. Specifically, I wanted to see the proportion of directories that would be “lost” if the top one or two contributors left the project. I ignored the individual files at the root level. The results look like this:

Database

Directories (total)

Directories lost (1 dev gone)

Directories lost (2 devs gone)

Redis

6

0 (0.0%)

0 (0.0%)

MariaDB

30

2 (6.7%)

5 (16.7%)

MongoDB

28

1 (3.6%)

7 (25.0%)

PostgreSQL

6

0 (0.0%)

5 (83.3%)

MySQL

30

1 (3.3%)

30 (100.0%)

SQLite

11

5 (45.5%)

11 (100.0%)

Here, a lower number is better (fewer directories impacted). So, Redis is pretty strong in this simulation, as no directories would take a hit. On the other end, we have MySQL and SQLite, with 100% of their directories potentially left unmaintained if the top two developers leave. PostgreSQL would lose 83% of its directories in a similar situation. These were the big surprises to me, although all this is aligned with the fact that they have a low bus factor (high risk) of 2.

MariaDB did pretty well, especially when compared to MySQL, which supports what I have been trying to say about how MariaDB is much more than a fork of MySQL in my articles and talks (see this and this, if you are curious).

Other Important Factors When Evaluating Open Source Projects

You should not rely merely on “bus factor” risk assessments. This is useful in mission-critical situations or when comparing projects that are even in other metrics that you might be using to compare and evaluate them. Here are some other aspects to look at:

Investigate Your Projects and Their Dependencies

I investigated the bus factor of other open source projects that I’m a big fan of, like MyBatis, Vaadin, and others, but I’ll let you do your own findings with the tool. Let me know if you find something interesting!

Appendix: Raw Impact Data

This appendix lists every directory and file at the root level that drops to a Bus Factor of 0 in the simulations.

1. MongoDB (Baseline: 7 - OK)

2. MariaDB (Baseline: 5 - OK)

3. Redis (Baseline: 5 - OK)

4. MySQL (Baseline: 2 - Low)

5. PostgreSQL (Baseline: 2 - Low)

6. SQLite (Baseline: 2 - Low)