Is mongo db suited for OLTP or DW operations?
What is the response time and effiency of mongodb in OLTP operations? Is it secure to use mongodb as a backend of a web application?
In mongodb itself we can do map reduce operation. Then what is the need for using hadoop integrator?
I need to know how strong is mongo db to use as a replacement for a BIG DW system ?
I'm using MongoDB for OLTP operations, currently I have 100+ operations/sec. and MongoDB can handle much more. In perfect case you can expect tens of thousands operations per second, but this number is hard to achieve in pratice.
Response time really depends on you replication/write preferences, because MongoDB gives you control over query execution(see CAP theorem). I don't know what you mean about effiency, I can say that insert operations is efficient enough(don't use updates for OLTP).
I have no experience with MongoDB security options, because all my web applications have full access to DB and I closed REST-API for public access.
Don't use MongoDB's MapReduce for large datasets, you have to trust me :). This is pain! I found Aggregation Framework suitable for large variety of operations with large datasets(Gb's of date). If it's not your case, try Hadoop's implementation on MapReduce, I don't have such experience, but always want to try.
As an option you may consider Hadoop's HDFS as main storage and something like messagepack as binary format. I heard about such solution.