How to hande joins in Mongodb?
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I have two tables in PostgreSQL:
urls (table with indexed pages, host is indexed column, 30 mln rows)
hosts (table with information about hosts, host is indexed column, 1mln rows)

One of the most frequent SELECT in my application is:
SELECT urls.* FROM urls JOIN hosts ON urls.host = hosts.host WHERE urls.projects_id = ? AND hosts.is_spam IS NULL ORDER by urls.id DESC, LIMIT ?
In projects which have more than 100 000 rows in urls table the query executes very slow.

Since the tables has grown the query is execution slower and slower. I've read a lot about NoSQL databases (like MongoDB) which are designed to handle so big tables and i'am taking into consideration move my data to MongoDB. Everything would be easy, if i didn't have to check hosts table during selecting data from urls table. I've heard that MongoDB doesn't support joins, so my question is how to solve above problem? I could put information about host in urls collection, but the field hosts.is_spam could be updated by user and i would have to update the whole urls collection. I don't know it it is right solution.

I would be greatful for any advices.

