When to use solr and why to use solr
Today I searched why use solr on google, the original text is as follows, I personally think it is very well written
Assuming the user has a relational DB, why use Solr? If your use case requires a person to type words into a search box, you want a text search engine like Solr.
Databases and Solr have complementary strengths and weaknesses. SQL supports very simple wildcard-based text search with some simple normalization like matching upper case to lower case. The problem is that these are full table scans. In Solr all searchable words are stored in an "inverse index", which searches orders of magnitude faster. For a more complete description of Solr's features, see http://lucene.apache.org/solr/features.html.
The original link is: https://wiki.apache.org/solr/WhyUseSolr
said so much, just to explain when you should use solr: full-text search.