How does the indexing of Maven artifact repositories work

5
votes

I would like to understand how the indexing for the artifact repositories like Nexus and Artifactory works. What benefit does it provide? I mean -- how does it help and what is the logic that's used when resolving artifacts?

My understanding is that the Lucene indexes contain information concerning which artifacts are presents in a given proxied repository or group and that once these indexes have been downloaded, you can easily check if a remote repository contains the artifact you're looking for and you can try to resolve it from the repositories which have it. Is this the only use? Is the index also queried for local resolutions (because each repository does have an index)...? How does this actually work?

3
mavennexusartifactorymaven-indexer

3 Answers

2
votes

As Mark already said, Maven Index is all about searching (either server side, where search is exposed over UI, or using REST) or client side like for example M2E does (typical example is code completion in POM editor, where context hints uses index to provide you Gs, As and Vs while adding dependencies for example).

Nexus does NOT use index to fulfil it's main functionality: serving up artifacts and/or proxying them, while it DOES maintain the index on the fly. Again, indexes are not used in "resolution" or any other way, except for Search UI and downstream publishing reason (for clients like M2E is).

For example "client side" usage of Maven Indexer, you can look at the examples here.

HTH,
~t~

10
votes

Artifactory doesn't use indexes for searching. We believe that indexes are the thing of the past, when machines were slow and couldn't handle large searches on the server side. Here is only partial list of why search indexes are bad:

  • Client need to download huge files before searching
  • The indexes are updated too rare to reflect frequent changes
  • System with search indexes requires special client to perform the search against
  • The client it toughly coupled with the index format.

Nowdays, when servers like Artifactory can provide real-time searching, exposed via UI for humans an API for tools like IDEs, the indexes are obsolete and supported in Artifactory only for compatibility with tools like m2eclipse.

3
votes

Repository indexing is all about searching. The Maven Eclipse plugin documentation describes the functionality:

Maintaining a server-side index makes Maven client operation more efficient. Server-side repository managers can use indexes to enable search interfaces and REST APIs for retrieving artifacts (Sonatype Nexus doesn't need a database).