How to implement the algorithm for selecting relevant articles?

Question

Algorithms

Good afternoon!
The situation is as follows: there is a site with articles and answers to frequently asked questions, and there is a forum where these questions are asked very often (there is only the subject of the question and the text of the message). I want to write a bot that would pick up articles from the site and send them to users automatically.
There are no problems with getting articles from the site or how to implement this business technically, but there is a problem with the algorithm. I don’t understand how it is better to implement this, maybe there are some ready-made solutions, for example, to compare two texts and determine their relevance .. Tell me.
Thanks in advance for the replies.

Answer 1

There is Sphinx , Google ElasticSearch

Answer 2

start https://www.elastic.co/guide/en/elasticsearch/guid...
+ Technostrim search course
+ https://tech.yandex.ru/tomita/
1) when indexing into a separate tabla - keywords of the article essence
2) compare with the request