What is CouchDB? #2: Guidelines & Use Cases posted Wednesday, September 3, 2025 by The Neighbourhoodie Team CouchDBOffline FirstDistsysReplication

Welcome back! In part one of this series we covered CouchDB’s headline features to understand what makes this database unique. By the end of this second part, you should have a better idea of when and why to use CouchDB. We’ll look at some of the scenarios in which you’ll want to consider it, and look at real world examples.

Let’s start where all longstanding relationships start: by getting to know CouchDB’s values and the principles they inform.

CouchDB Guiding Principles#

We’ve already seen in part one that CouchDB aimed to be a realist amongst idealists — a database capable of performing, often in spite of the hardware and network in which it finds itself. We know the headline features a bit by now, so let’s get to know the decision-making “engine” behind them.

Reliable#

It should never lose data.

Ever.

In our previous article we pointed to all the lengths that CouchDB goes to to ensure you never, ever, ever end up with corrupted or missing data. Decisions will always be made in favour of reliability. If a feature in CouchDB couldn’t ensure this, it simply isn’t built; CouchDB is founded upon reliability, not retro-fitted for it.

Easy to Use (Relax™)#

You may have seen the old CouchDB logo around, pixelating as it recedes into the internet’s memory. The figure isn’t around anymore, but “Time to Relax” is still the boot-up greeting.

“Relax” is a big part of the CouchDB approach. It manifests not just in things like providing UI out-of-the-box and an HTTP API, but in being conceptually and operationally easy to grasp. That doesn’t just mean that CouchDB is easy to understand and set up quickly, it also means it’s difficult to break. And that includes breaking changes in an upgrade.

The CouchDB team put great effort into ensuring that you can upgrade with reduced risk and enjoy new features without comprehensively reconfiguring.

As Simple As Possible But Not Simpler#

There’s a fine line between easy-to-grasp and reductionist. CouchDB treads the right side of this line. We’ve already seen that CouchDB leaves features that could compromise data integrity on the table. It guards ease of scaling the same way: CouchDB deliberately only adds features that will grow with you. That may not be all the features on the checklist, but for engineers it means growing is no sweat. You don’t have to re-write your app while your database scales indefinitely.

And there we have it — the three guidelines that inform CouchDB and keep it irreplaceable.

Is It Right For My Project?#

We mentioned that CouchDB leaves some things on the table in order to do what it does exceptionally well. What gets left off? And what projects does that make it suitable for?

Trading Off#

Keeping data safe, being easy to use, and spectacularly reducing the risk of breakage has these implications:

• The first trade-off is speed. CouchDB is not a slow database, but there are document-oriented databases that have been designed to favour speed and are therefore faster. If you need a fast database (and don’t mind losing data at equal speed), there may be a better DB for you than CouchDB.
• The second trade-off is disk space. CouchDB uses more disk space than some other databases. Luckily, this is something that’s getting cheaper as time goes by.

Trading Up#

So when does it make sense to use no other database than CouchDB? Some of these will have already become clear:

• You’ll scale fast.
  • We’ve seen that CouchDB makes it incredibly easy to add another instance: it promises you won’t have to re-write your app to do so. If you know you’ll outgrow a single machine quickly, use CouchDB.
• You can’t lose a thing.
  • As we’ve seen, CouchDB always makes decisions that favour data integrity. If losing a record or change is unacceptable, use CouchDB.
• Your internet connection isn’t great.
  • CouchDB has its own replication protocol that makes it an exceptional choice for offline-first and local-first software. If you can’t tolerate downtime, use CouchDB.
• You’d rather use an API than manage proprietary drivers.
  • CouchDB’s HTTP JSON API and the open standards it uses make it highly interoperable. If you want to build and iterate quickly, use CouchDB.

You can read from current CouchDB users why these trade-offs are worth it, and if you do, you’ll discover the two features most coveted by CouchDB users, namely replication and the _changes feed.

Unparalleled Feature #1: Replication#

We’ve covered this a bit already, so let’s introduce something new about it: CouchDB’s sibling technology, PouchDB. Written in JavaScript, it’s designed to save your work locally on your device and then sync with your CouchDB when you’re back online, and can also be set up to automatically handle conflicts. Where automation won’t do, you can use CouchDB’s built-in UI, Fauxton, if you haven’t built your own conflict UI. No last-write-wins behaviour, aka no randomly losing customer data.

Don’t get caught out with inconsistent replication! Can you distinguish a complete sync engine from an imposter? Image source

Unparalleled Feature #2: _changes Feed#

The second feature CouchDB users love most is the changes feed. Social media feeds have normalised the timeline, but CouchDB pioneered an append-only log of all and any changes in a database. You can use this to build real-time UIs and reactive backends, including for multi-user apps.

Real-Life Examples#

As my colleague Jan Lehnardt recently got to share, CouchDB makes some incredible things happen. There’s a very good chance you rely on things that CouchDB has a hand in delivering but don’t know it. CouchDB is behind more than you might realise. And if you live in Bavaria, that includes your Covid vaccination. Without compromising any person or company’s privacy, let’s look at more examples.

Extreme Storage, XCDR Use Case: Broadcasting#

Let’s say you’re a globally active, national broadcaster who needs to choose a database (and no, you haven’t fallen through the looking glass — this is not a prompt). Your requirements might look something like:

• Store and maintain a content library
• that captures journalist’s submissions
• from the field, wherever they are in the world,
• that can later be streamed to broadcast centres
• across the country and the world
• even in emergencies
• in real-time
• even if one data centre is unavailable.

This is a heavy lift. But CouchDB is perfect for the job and helps ensure the news goes out whether it’s business as usual or not.

• Extreme scaling features mean it can just keep on and on accepting data without hassle — provided you’re adding adequate storage space.
• CouchDB’s integrity features ensure footage is transmitted with practically no risk of corruption over unstable networks.
• Replication features means it handles Cross Data Centre Replication (XDCR) from the get-go. If one data center goes down — even during a broadcast — another will pick it up in real-time.
• Replication features also mean CouchDB supports geodistribution out-of-the-box, contributing to reduced latency and increased redundancy.

It’s not just the news: entertainment also has significant storage needs. If you’ve been looking for a place to neatly store more data than you thought you’d be generating (and make it easy), CouchDB is your database. Image: “The tardis” by sinepax.

Offline Business Use Cases: Remote Servicing#

Our team has been lucky enough to support many clients with this need, so you can read about one of these use cases in more detail on our website.

Imagine these requirements:

• You need to analyse cooling fluid variables
• for each of your customer’s machines
• in their workshops,
• no matter how remote, offline, subterranean or (Faraday) caged away,
• correctly correlated with machine inventory
• referring to measurement history if needed,
• with role-based access.

Once again, CouchDB does this with ease.

• The app that solves these problems pre-loads customer and machine data on-device so the field team enjoys practically full offline functionality. The only thing they can’t do is user administration.
• Per machine and per facility inventory and measurement history, report generation, task management and machine setup all happen offline.
• Not to mention CouchDB handles complex user roles, in-app warnings and email notifications with ease.

Distributed Emergency Use Case: The Ebola Project#

We’ve looked at a national (public) service and a business use case. Now for something that really hits home, and if you haven’t yet, you can watch a talk about this project from the Local First Conf. This is a humanitarian use case, so setting the scene is going to be quite different, and we’ll describe more of the problem-solving that went into it.

It’s 2013–2016 and the Ebola outbreak in West Africa is heavily affecting Sierra Leone, Liberia and Guinea, and to a lesser degree Nigeria and Mali. No vaccine exists at the time, and the case fatality risk varies from 25-90%. For perspective, at its absolute peak, COVID-19’s case fatality risk just exceeded 5%. Contract tracing is one of the most important interventions at this point.

You need to:

• Find everybody who has symptoms or has tested positive and quarantine them,
• find anyone they’ve been in contact with since showing symptoms
• and monitor them for up to 21 days,
• placing anyone who shows symptoms in quarantine.

This was already happening on paper, so:

• Using CouchDB, the team built an offline capable mobile app with bidirectional sync for volunteers that had a zero friction UI to help process as many people as possible.
• Thanks to the _changes feed, the team also built cloud-aggregated real-time dashboards to direct relief efforts.
• They put together a call center and assigned individual IDs to anyone who was quarantined so that families — potentially hundreds of miles away — could call to get updates.

The call center presented some interesting challenges:

• Each laptop had PouchDB, which would replicate the full call center data onto the local machine.
• The amount of data and data churn showed that the hardware and software available at the time weren’t efficient enough: load times were too slow and would get in people’s way.
• The solution was, luckily, not difficult to implement. Because PouchDB is designed for multiple environments that handle data persistence differently, there’s an abstraction layer in the middle that lets you pick how to store data. One of these is an HTTP adapter, which means it turns PouchDB into a CouchDB frontend client. Removing the storage component of PouchDB and getting it to talk to CouchDB directly was a one line code change, because they’re built for such situations.
• Had the call center had reliable internet connection, this solution would have worked. But as it was, each call center interaction was fraught with delays and timeouts. Thankfully, CouchDB is really good in these situations.
• The next solution was to put a CouchDB on one of the laptops that acted as the local server, had low latency and was always available. It would use the unstable network to asynchronously up and download everything to and from the cloud. The refined call center solution required 0 code changes — that’s just the kind of thing CouchDB can support without extra tinkering.

There’s more to the story than we’ll go into here. CouchDB was instrumental in stemming the Ebola epidemic and contributing to vaccination trial efforts and insights that resulted in the first approved vaccine being delivered by December 2016. Watch the talk for all the details.

What’s Next#

You should now have a good idea of when and why to use CouchDB. In the third and final part of this series, we’ll look at the CouchDB ecosystem and find out more about the community. Until next time!

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