As Dynamodb store the data in form of key value pairs, where key is the sort of primary key and value is the data associated with it.I want to know whether dynamo db actually understands the value(json)?By value I mean the json object associated with a key(a row in RDBMS).Does dynamo db understands that there are some attributes and there are some value of attributes that it is gonna store?
Context : I have a person table in dynamo db that has different attributes, say 100, and one of them is age, now suppose there is some requirement that i want to get some records based on age. If dynamo db go each entry one by one and then read its record and suppose each record is pretty large, then does dynamo db reads entire data of record or can it access only age attribute in constant time regardless of size of the record?
Does dynamo db understands that there are some attributes and there are some value of attributes that it is gonna store?
No, it does not.
DynamoDB is a "wide column" style of NoSQL database. While the schema isn't defined beyond the primary key at table construction time, the querying abilities are limited to primary keys or secondary indexes. Creating Global Secondary Indexes allows you to query against other attribute values. Local Secondary Indexes can be queried too, but they're a bit of an odd duck. See here for a good comparison of the two secondary index types.
If your needs do include querying inside the attributes, check out some of the "document-oriented" style of NoSQL databases, of which MongoDB is the one most people think of. If you're already embedded in the AWS ecosystem and don't want to break out of it, AWS offers DocumentDB as a MongoDB-compatible service managed by AWS.
Wide-column and document-style data stores have different pro's & cons. Generally-speaking, the wide-column approach is better for extreme scalability at consistent cost & speed, whereas the document-oriented approach gives more flexibility as your data access patterns evolve over time. Choose the one that suits your needs the best.