Few of the most confusing terms in Solr world are: Core, Collection and Index.
We try to provide an informal way of describing these hot keywords:
In distributed search, Collection is a logical index spread across multiple servers. Core is that part of server which runs one collection.
In non-distributed search,
Single server running the Solr can have multiple collections and each of those collection is also a core.
So collection and core are same if search is not distributed.
Collection per server is called a core.
One Solr server can have many cores.
By virtue of #1, it will have same number of collections as well.
Roughly speaking, Collection is nothing but a logical index.
(Example usage for multiple collections: If two teams in same group are not big enough to justify
a full Solr server of their own. But they also do not want to mix their data in a single
index. They can then create separate collections/indexes which will keep their data separate).
Its better to use a separate Solr Cloud rather than create collections if the data for a collection is big enough.
Got a thought to share or found a bug in the code? We'd love to hear from you: