MongoDBDataMigrateShell.js

var node = db.getSiblingDB("db1");
var rs = db.getSiblingDB("db2");

function prepareMsgIds(table) {
	var iter = table.find({"_id":{"$regex":"^sq:"}});
	return iter;
}

//FIXME: performace
function districtArray(array) {
	var result = new Array();

	//FIXME: performace
	function indexOf(arr, item) {
		var t = false;
		for(var k = 0; k < arr.length; k++) {
			if(arr[k]._id === item._id) t = true 
		}
		return t; 
	}

	for(var i = 0; i < array.length; i++){
		if(!indexOf(result, array[i])) result.push(array[i]);
	}
	return result;
}

function jsonFormattor(prepares) {
	function idExtractor(id) {
		var uid = id.replace("sq:", "");
		return uid;
	}
	function tsExtractor(msgId) {
		var head = msgId.indexOf("~");
		var tail = msgId.lastIndexOf("~")
		var timestamp = msgId.slice(head+1, tail);
		return Number(timestamp);
	}
	function toJson(uid, msgId, timestamp) {
		return {
			"_id": uid + ">" + "qm" + ">" + msgId,
			"e": msgId + "<" + "qm",
			"t": timestamp
		};
	}

	var tmpRs = [];
	for(var i = 0; prepares.hasNext(); i++) {
		var item = prepares.next();
		var idQ = item.s.q
	
		for(var k = 0;  k < idQ.length; k++) {
			tmpRs.push(toJson(idExtractor(item._id), idQ[k], tsExtractor(idQ[k])));
		}
	}
	return tmpRs;
}

//batch insert unread msgs ids
function batchInsertTo(table, dataArr, batchSize) {
	var errors = [];
	for(var n = 0; n < dataArr.length / batchSize; n++) {
		var batch = dataArr.slice(n * batchSize, (n + 1) * batchSize);
		table.insert(batch);
		var lastErr = table.runCommand({"getLastError": 1, "w": 1 });
		if(lastErr.err != null) errors[n] = lastErr;
	}
	return errors;
}

(function() {
	var errors = batchInsertTo(rs.RS, districtArray(jsonFormattor(prepareMsgIds(node.Node))), 100);
	printjson(errors);
})()

//now the unread msg id queue 
/*{
    "_id" : "sq:f:100000235239372",
    "s" : {
        "c" : 2,
        "q" : [ 
            "ms:f:100002966342971~1384949610662~71", 
            "ms:f:100002966342971~1384949611774~9"
        ]
    }
}*/

//will transforms to 
/*{
    "_id" : "q:11111111>qm>ms:q:ojstuv~1387522125766~9210",
    "e" : "ms:q:22222222222~1387522125766~9210<qm",
    "t" : NumberLong(1387522131223)
}*/