how to wcf restfull service retun lakhs of recors?

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C#

web.config

In my wcf restfull service using Steam Return type. The below function Returns 1 lake
Records(Each Rows Having 18 Columns). If records more than 1 lakh its getting memory error.

public Stream GetSession()
   {
       //based upon business logic send back a session id
       string sessionXml = String.Format("<Session>{0}</Session>", Guid.NewGuid().ToString());
       //Convert the stream into string
       Encoding encoding = Encoding.GetEncoding("ISO-8859-1");
       WebOperationContext.Current.OutgoingResponse.ContentType = "text/plain";
       byte[] returnBytes = encoding.GetBytes(sessionXml);
       //Send it back
       return new MemoryStream(returnBytes);
   }

But In Case I need Return at-lest 50 lakhs Records.
Please Help me.
Thanks In Advance...