How Important is a Repository Manager?

May 15, 2016 · 3 min read ·

Do you know how many downloads are done from Maven Central during a month? I was not aware of that as well. As a PMC member of the Apache Maven Project I have the privilege of having access to the statistics of Maven Central.

So I checked the statistics of Maven Central. I can tell you that in the groupId org.apache.maven were more than 27 million (28,933,147) downloads in April 2016. This means in other words more than 964,438 downloads per day or more than 11 downloads per second.

The following chart gives you an impression of the trend over the last year.

 1| Period  | Downloads |
 2| ------- | --------- |
 3| 04.2015 |  7,847,302|
 4| 05.2015 |  9,179,019|
 5| 06.2015 |  9,916,411|
 6| 07.2015 | 13,908,913|
 7| 08.2015 | 14,548,666|
 8| 09.2015 | 15,965,751|
 9| 10.2015 | 16,477,754|
10| 11.2015 | 16,404,231|
11| 12.2015 | 19,106,721|
12| 01.2016 | 19,607,497|
13| 02.2016 | 21,419,699|
14| 03.2016 | 27,469,986| 
15| 04.2016 | 28,933,147|

What are the consequences for you as a consumer of Maven Central? You should think about the load you are continuously producing on the infrastructure of Maven Central.

But now the question arises what can you do? The simple answer is: Use a repository manager.

It does not matter if you are in a corporate environment or more or less alone. By using a Repository Manager you will reduce the load on Maven Central which is only one aspect of the story.

One other very important aspect is that you can release artifacts in your corporate environment into your repository manager without making it available to the public via Maven Central or other services like that.

And of course we should think about the future:

1A long time ago in a galaxy far far away...

What does this mean? Simply if Maven Central might be down or vanishes away some time in the future you have your own repository manager with all the artifacts needed to build your own artifacts within your network.

There are a few rules to use Maven Central to keep the stability of Maven Central. The most important one is that an released artifact is immutable. This means if you have published it to Maven Central the artifact can not be changed anymore. There does not exist an exception to that rule.

The NPM Problem has shown that those rules are very good rules. I did not understand why someone could simply change or delete artifacts from a repository that is consumed by other people. This breaks any reliability.

If it happens that someone really has to remove an artifact from Maven Central because of Copyright issues, then you are safe by using a repository manager cause you have a copy in your repository.

So running a repository manager is always a wise decision.