How can we use MongoDb with postgresql?

Which will be a better to use 1) Mongodb with Redis or 2) Mysql with Memcached?

• Many a times question comes like "What is the use of Redis with Mongodb ?" I have seen the answers as if Mongodb is equivalent to Mysql then Redis is equivalent to Memcached. I have a doubt that which one is better to use ? 1) Mongodb with Redis  , OR 2) Mysql with Memcached.

• Answer:

  Edit Got corrected by a friend offline: 1) Practically speaking, Redis IS a good replacement for Memcached. 2) MongoDB is more than an in-memory DB. Consecutively, if you are using Mongo as a large data storage and considering a Memcached in front of it, Redis is a reasonable alternative. Original Memcached is an in-memory caching layer. Redis and MongoDb are in-memory databases. They are not designed to play well together: you are better off dedicating all the memory to Redis alone or to MongoDb alone. (Memcached technically can be used as a database on its own, but you don't want to be doing it.) The choice between MySql and Redis/MongoDb boils down to SQL/NoSQL decision. Without extra domain knowledge, my vote goes to NoSQL. The launch of Facebook Presto keeps showing that NoSQL is getting more and more powerful. But I'm biased. For extremely convincing arguments see http://howfuckedismydatabase.com/mysql/ and the whole http://howfuckedismydatabase.com/ in general.