What is the index in the Solr index in database?

In a DBMS index is an object which improves performance in the search what field.
Solr - I know that collections are like tables in a DBMS, documents as records in the database, and the index - what is it? Sometimes I read and do not understand that either, but then realize that the index is the analog of the collection. But it is clear that it is not. Someone can explain what is index in Solr?
June 14th 19 at 20:45
2 answers
June 14th 19 at 20:47
The index in SOLR is the equivalent of the Glossary in the book: a unique sequence of characters within which there are links to the documents themselves, where these sequences occur.
This custom link table where the records are arranged alphabetically and increase in length, forming a "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
June 14th 19 at 20:49
Yes all the same.
For a faster search.

But in the case of, for example, a relational DBMS more like something you can live without index (but bad).
In the case of full-text search Solr, Sphinx - with no index at all pointless.

If you go back to collections, some collections exist only in the form of indexes.

If we turn to the classics of the database index for faster searches and data are two different things.
Index you can safely delete and re-create (to re-generate based on the data).
It will only affect the search speed.

But with some types of collections it will not work. For them the index is the data. Removes the index - nothing more find.

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