Compare Mongo read behavior

reads.js

/**
 * Initialize the database collection for querying.
 */
var init = function() {
    db.foo.drop();
    for (var i = 0; i < 10; ++i) {
        for (var j = i; j < 100000; j += 10) {
            db.foo.insert({x: j, y: j});
        }
    }
    db.foo.ensureIndex({x:1});
    db.foo.ensureIndex({y:1});
}

/**
 * Execute a given number of queries stepping through a range of values.
 *
 * @param integer num
 * @param integer from
 * @param integer to
 * @return Total nscanned from all query explains
 */
var query = function(num, from, to) {
    var step = Math.floor((to - from) / num);
    var nscanned = 0;

    for (var i = from; i < to; i += step) {
        nscanned += db.foo.find({x: {$lt: i}, y: {$gt: (i - 20)}}).explain().nscanned;
    }

    return nscanned;
}

if (db.foo.count() !== 100000) {
    init();
}

var tests = [
    {
        name: "One batch of 100 queries in the 75-100k range",
        batches: [
            [100, 75000, 99999]
        ]
    },
    {
        name: "Four batches of 25 queries in the 0-25, 25-50, 50-75, and 75-100k ranges",
        batches: [
            [25, 0, 24999],
            [25, 25000, 49999],
            [25, 50000, 74999],
            [25, 75000, 99999]
        ]
    }
];

tests.forEach(function(test) {
    jsTest.log(test.name);

    var start = new Date();
    var btreeStart = db.serverStatus().indexCounters.btree;
    var info;

    test.batches.forEach(function(args, i) {
        print("batch " + (i + 1) + " nscanned: " + query.apply(null, args));
    });

    var end = new Date();
    var btreeEnd = db.serverStatus().indexCounters.btree;

    print("total time: " + ((end.getTime() - start.getTime()) / 1000));
    ["accesses", "hits", "misses", "resets", "missRatio"].forEach(function(stat) {
        print("btree." + stat + ": " + (btreeEnd[stat] - btreeStart[stat]));
    });
});

results.txt

[honeydew: FREE-14832_read_behavior] $ mongo reads.js 
MongoDB shell version: 2.0.6
connecting to: test

----
One batch of 100 queries in the 75-100k range
----

batch 1 nscanned: 1269469
total time: 3.379
btree.accesses: 0
btree.hits: 0
btree.misses: 0
btree.resets: 0
btree.missRatio: 0

----
Four batches of 25 queries in the 0-25, 25-50, 50-75, and 75-100k ranges
----

batch 1 nscanned: 324675
batch 2 nscanned: 974675
batch 3 nscanned: 975800
batch 4 nscanned: 325819
total time: 6.688
btree.accesses: 0
btree.hits: 0
btree.misses: 0
btree.resets: 0
btree.missRatio: 0



[honeydew: FREE-14832_read_behavior] $ mongo reads.js 
MongoDB shell version: 2.2.0-rc1-pre-
connecting to: test

----
One batch of 100 queries in the 75-100k range
----

batch 1 nscanned: 1269469
total time: 5.956
btree.accesses: 0
btree.hits: 0
btree.misses: 0
btree.resets: 0
btree.missRatio: 0

----
Four batches of 25 queries in the 0-25, 25-50, 50-75, and 75-100k ranges
----

batch 1 nscanned: 324675
batch 2 nscanned: 974675
batch 3 nscanned: 975800
batch 4 nscanned: 325819
total time: 11.918
btree.accesses: 0
btree.hits: 0
btree.misses: 0
btree.resets: 0
btree.missRatio: 0