android - Data driven app requirment -

android - Data driven app requirment -

i wanting build info driven app, app upload data, fetch info , sync data, 1 time devices connect net . confuse info driven app need integrate with, sql sever? cloud database? etc. in order synchronization 1000000 user

lets utilize whatsapp example, can advise me app whatsapp utilize store user info , allow others user fetch info want please??

a sqlite or sql? cloud database? http://www.rackspace.co.uk/cloud/servers/pricing ?

i know question vague, overall m lacking of knowledge online application need equip with.

thanks helping.

android ios database synchronization