mongodb/jstests/sharding/sharding_balance1.js

(function() {
'use strict';

var s = new ShardingTest({shards: 2, mongos: 1, other: {chunkSize: 1, enableBalancer: true}});

assert.commandWorked(s.s0.adminCommand({enablesharding: "test"}));
s.ensurePrimaryShard('test', s.shard1.shardName);

var db = s.getDB("test");

var bigString = "";
while (bigString.length < 10000) {
    bigString += "asdasdasdasdadasdasdasdasdasdasdasdasda";
}

var inserted = 0;
var num = 0;
var bulk = db.foo.initializeUnorderedBulkOp();
while (inserted < (20 * 1024 * 1024)) {
    bulk.insert({_id: num++, s: bigString});
    inserted += bigString.length;
}
assert.writeOK(bulk.execute());

assert.commandWorked(s.s0.adminCommand({shardcollection: "test.foo", key: {_id: 1}}));
assert.lt(20, s.config.chunks.count({"ns": "test.foo"}), "setup2");

function diff1() {
    var x = s.chunkCounts("foo");
    printjson(x);
    return Math.max(x[s.shard0.shardName], x[s.shard1.shardName]) -
        Math.min(x[s.shard0.shardName], x[s.shard1.shardName]);
}

function sum() {
    var x = s.chunkCounts("foo");
    return x[s.shard0.shardName] + x[s.shard1.shardName];
}

assert.lt(20, diff1(), "big differential here");
print(diff1());

assert.soon(function() {
    var d = diff1();
    return d < 5;
    // Make sure there's enough time here, since balancing can sleep for 15s or so between
    // balances.
}, "balance didn't happen", 1000 * 60 * 5, 5000);

s.stop();
})();