What is the difference between an index in Solr and an index in a DBMS?

Question

Solr

In a DBMS, an index is an object that improves performance in searching for some field.
Solr - I know that "collections" are like tables in a subd, documents are like records in a subd, and an index is what it is? Sometimes I read, and either I don’t understand, or something, but somehow I understand that an index is an analogue of a collection. But it is clear that this is not the case. Can someone explain what is an index in Solr?

Answer 1

An index in SOLR is like a glossary in a book: unique sequences of characters, within which there are links to the documents themselves, where these sequences occur.
This is a custom link table where the entries are ordered alphabetically and increasing in length, forming a "flat tree".
1. https://lucene.apache.org/solr/guide/6_6/overview-...
2. https://github.com/apache/lucene-solr
3. apache-mirror.rbc.ru/pub/ apache/lucene/solr/7.0.0

Answer 2

Yes, all too.
For faster searching.
But in the case of, for example, a relational DBMS, you can still somehow live without an index (but badly).
Then in the case of full-text search Solr, SphinxSearch - without an index is generally meaningless.
Back to collections, some kinds of collections exist only as indexes .
If you turn to the classics of the database - the index to speed up the search and the data itself are two different things.
The index can be painlessly deleted and recreated (regenerated based on the data).
This will only affect the search speed.
But with some types of collections, this will not work. For them, the index is the same data. If you delete the index, you won't find anything else.