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# Frequently Asked Questions

## Development process

### Why is there a commercial version of ejabberd?

Different needs for different users. Corporations and large scale deployments are very different from smaller deployments and community projects.

While we put a huge development effort to have a product that is on the edge of innovation with ejabberd community version, we are requested to provide a stable version with long term commitment and high level of quality, testing, audit, etc.

Maintaining such a version in parallel to the community version, along with extremely strong commitment in terms of availability and 24/7 support has a tangible cost. With ejabberd business edition we commit to a level of scalability and optimize the software until it is performing to the level agreed with the customer.

Covering all those costs, along with all our Research and Development cost on ejabberd community in general is the real reason we need a business edition.

The business edition is also a way for our customers to share the code between our customers only, thus retaining a huge competitive edge for a limited time (See next section).

So, even if you are not using our business edition, this is a great benefit for you as a user of the community edition and the reason you have seen so many improvements since 2002. Thanks to our business edition customers, ejabberd project itself is a major contributor to Erlang and Elixir community.

### Does ProcessOne voluntarily hold some code in ejabberd community to push toward the business edition?

No. We never do that and have no plan doing so with the code we produce and we own.

However, when the code is paid by customer, they retain the ownership of the code. Part of our agreement is that the code produced for them will be limited to a restricted user base, ejabberd business edition until an agreed time expires, generally between 6 months and 1 year.

This is extremely important for both the users of the commercial edition and the users of the community edition:

- For the business edition customers, this is a way to keep their business advantage. This is fair as they paid for the development.

- This is also a great incentive for our customers as they benefit from development for other customers (I guess they agree for the reciprocal sharing of their own code with customers).

- This is fair for the community as the community edition users know they will benefit from new extremely advanced features in a relatively near future. For example, websocket module was contributed to ejabberd community as part of this process.

This is the model we have found to be fair to our broader user base and lets us produce an amazing code base that benefits all our users.

This dual model is the core strength of our approach and our secret sauce to make sure everyone benefits.

## Performance

### Is ejabberd the most scalable version?

Yes. Definitely. Despite claims that there is small change you can make to make it more scalable, we already performed the changes during the past year, that make those claims unfunded:

- ejabberd reduced memory consumption in 2013 by switching to binary representation of string instead of list. This can reduce given string by 8.

- We have improved the C code performance a lot, using new Erlang NIF. This provides better performance, removes bottlenecks

- We have a different clustering mechanism available to make sure we can scale to large clusters

This is a common misconception, but our feedback for production service on various customer sites shows that ejabberd is the most scalable version. Once it is properly configured, optimized and tuned, you can handle tens of millions of users on ejabberd systems.

... And we are still improving :)

As a reference, you should read the following blog post: ejabberd Massive Scalability: 1 Node — 2+ Million Concurrent Users

### What are the tips to optimize performance?

Optimisation of XMPP servers performance, including ejabberd, is highly dependent on the use case. You really need to find your bottleneck(s) by monitoring the process queues, finding out what is your limiting factor, tune that and then move to the next one.

The first step is to make sure you run the latest ejabberd. Each new release comes with a bunch of optimisations and a specific bottleneck you are facing may have gone away in the latest version.

For perspective, ejabberd 15.07 is 2 to 3 times more efficient in memory, latency and CPU compared to ejabberd 2.1.

You should also make sure that you are using the latest Erlang version. Each release of Erlang comes with more optimisation regarding locks, especially on SMP servers, and using the latest Erlang version can also help tremendously.

## Erlang support

### Is ejabberd conforming to the best Erlang practices?

Yes. Our build system is primarily based on rebar. However, as we are multiplatform and need to run in many various environments, we rely on a toolchain that can detect required library dependencies using autotools.

This gives developers and admins the best of both worlds. A very flexible and very versatile build chain, that is very adequate to make sure ejabberd can be used in most operating systems and even integrated in Linux distributions.