Storing and retrieving large data in C# [on hold]

Currently, I am working on a project where I need to bring approx 100 Millions row of data from a table on to client code to retrieve the data faster.

The loading of data would be one time process so instead of making a database call I want to store it locally. somewhere in collection/xml and define function to get the row details:

I am not in a position to look into DB structure as its a third party vendor and I have to optimize the response time.

SO i want to save time for DB connection and return the data from any existing collection/ customised collection/xml/json.

It could be a local file stored having all these 10M rows and fetch the data from that one.

Pls suggest.

lets say: I have to

public list<mylist> GetDetailsbyId (int id)
{
//implementation
}

public list<mylist> GetDetailsbyName (string name)
{
//implementation
}

Can any one suggest what would be ideal way to store these large volume of data in c# code. I am thinking of XML.