text: 
  t = db.mr_bench;
  t.drop();
  
  function getRandomStr(L) {
      var s = '';
      var randomchar = function() {
          var n = Math.floor(Math.random() * 62);
          if (n < 10)
              return n;  // 1-10
          if (n < 36)
              return String.fromCharCode(n + 55);  // A-Z
          return String.fromCharCode(n + 61);      // a-z
      };
      while (s.length < L)
          s += randomchar();
      return s;
  }
  
  t.ensureIndex({rand: 1}, {unique: true});
  
  largeStr = "aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa";
  while (largeStr.length < 512) {
      largeStr += largeStr;
  }
  largeStr = largeStr.substr(512);
  
  for (i = 0; i < 100000; ++i) {
      t.save({rand: getRandomStr(20), same: "the same string", str: largeStr});
  }
  
  emit = printjson;
  count = t.count();
  
  function d(x) {
      printjson(x);
  }
  
  m = function() {
      emit(this.rand, {id: this._id, str: this.str});
  };
  
  m2 = function() {
      emit(this.same, this.rand);
  };
  
  r = function(k, vals) {
      var tmp = {};
      vals.forEach(function(i) {
          if (typeof(i) == 'string') {
              tmp[i] = true;
          } else {
              for (var z in i)
                  tmp[z] = true;
          }
      });
  
      return tmp;
  };
  
  // following time limits are passing fine on a laptop with a debug build
  // so should always pass in theory unless something is wrong: GC, too much reducing, etc
  
  // 1st MR just uses random unique keys, with no reduce involved
  // this should be straightforward for perf, but could lead to OOM if settings are bad
  assert.time(function() {
      res = db.runCommand({mapreduce: "mr_bench", map: m, reduce: r, out: "mr_bench_out"});
      d(res);
      assert.eq(count, res.counts.input, "A");
      x = db[res.result];
      assert.eq(count, x.find().count(), "B");
      return 1;
  }, "unique key mr", 15000);
  
  // 2nd MR emits the same key, and a unique value is added as key to same object
  // if object is kept in ram and being reduced, this can be really slow
  assert.time(function() {
      res = db.runCommand({mapreduce: "mr_bench", map: m2, reduce: r, out: "mr_bench_out"});
      d(res);
      assert.eq(count, res.counts.input, "A");
      x = db[res.result];
      assert.eq(1, x.find().count(), "B");
      return 1;
  }, "single key mr", 20000);
  