mongodb count benchmark index

bench.js

var filters = ['abcd', 'efgh', 'ijkl', 'mnop', 'qrst', 'uvwx', 'yz'];
var flen = filters.length;
var n = 1000000;
var max = -1;

function printInterestingStats(explain) {
   print("   cursor: " + explain.cursor);
   print("   nscanned: " + explain.nscanned);
   print("   scanAndOrder: " + explain.scanAndOrder);
   print("   millis: " + explain.millis);
}

function getRandomString() {
   return ''+Math.floor(Math.random()*max);
}

function getRandomFilter() {
   return filters[Math.floor(Math.random()*flen)];
}

function initialInsert() {
   for( var j = 0; j < flen; j++) {
      for( var i = 0; i < max; i++) {
         var dStr = ''+i;
         var fStr = filters[j];
         db.test9.insert(
            {
               filter: fStr,
               data: dStr,
               count:1
            }
         );
      }
   }
}

function updateCounts() {
   for( var i = 0; i < n; i++) {
      var dStr = getRandomString();
      var fStr = filters[Math.floor(Math.random()*flen)];
      db.test9.update(
         {
            filter: fStr,
            data: dStr
         },
         {
            $inc: {count: 1}
         }
      );
   }
}

function bench() {
   max = 100000;
   print("benchmarking with index on {filter,data}, 700K docs");
   db.test9.drop();
   db.test9.ensureIndex({filter: 1, data: 1});
   d = new Date();
   initialInsert();
   tot = new Date() - d;
   per = tot/(flen*max);
   print("initialInsert of "+(flen*max)+" done in: " + tot + "ms, "+per+"ms per insert");
   d = new Date();
   updateCounts();
   tot = new Date() - d;
   per = tot/n;
   print("updateCounts "+ n +" times done in: " + tot + "ms, "+per+"ms per update");
   print("explain find({filter:\"abcd\"}).sort({count:-1}): ");
   printInterestingStats(db.test9.find({filter:"abcd"}).sort({count:-1}).explain());
   print("explain find({filter:\"abcd\"}).limit(100).sort({count:-1}): ");
   printInterestingStats(db.test9.find({filter:"abcd"}).limit(100).sort({count:-1}).explain());
   
   print("benchmarking with index on {filter,data} and {filter, count}, 700k docs");
   db.test9.drop();
   db.test9.ensureIndex({filter: 1, data: 1});
   db.test9.ensureIndex({filter: 1, count: -1});
   d = new Date();
   initialInsert();
   tot = new Date() - d;
   per = tot/(flen*max);
   print("initialInsert of "+(flen*max)+" done in: " + tot + "ms, "+per+"ms per insert");
   d = new Date();
   updateCounts();
   tot = new Date() - d;
   per = tot/n;
   print("updateCounts "+ n +" times done in: " + tot + "ms, "+per+"ms per update");
   print("explain find({filter:\"abcd\"}).sort({count:-1}): ");
   printInterestingStats(db.test9.find({filter:"abcd"}).sort({count:-1}).explain());
   print("explain find({filter:\"abcd\"}).limit(100).sort({count:-1}): ");
   printInterestingStats(db.test9.find({filter:"abcd"}).limit(100).sort({count:-1}).explain());
   
   max = 1000000;
   print("benchmarking with index on {filter,data}, 7M docs");
   db.test9.drop();
   db.test9.ensureIndex({filter: 1, data: 1});
   d = new Date();
   initialInsert();
   tot = new Date() - d;
   per = tot/(flen*max);
   print("initialInsert of "+(flen*max)+" done in: " + tot + "ms, "+per+"ms per insert");
   d = new Date();
   updateCounts();
   tot = new Date() - d;
   per = tot/n;
   print("updateCounts "+ n +" times done in: " + tot + "ms, "+per+"ms per update");
   print("explain find({filter:\"abcd\"}).sort({count:-1}): ");
   print("too big to sort without limit!");
   //printInterestingStats(db.test9.find({filter:"abcd"}).sort({count:-1}).explain());
   print("explain find({filter:\"abcd\"}).limit(100).sort({count:-1}): ");
   printInterestingStats(db.test9.find({filter:"abcd"}).limit(100).sort({count:-1}).explain());
   
   print("benchmarking with index on {filter,data} and {filter, count}, 7M docs");
   db.test9.drop();
   db.test9.ensureIndex({filter: 1, data: 1});
   db.test9.ensureIndex({filter: 1, count: -1});
   d = new Date();
   initialInsert();
   tot = new Date() - d;
   per = tot/(flen*max);
   print("initialInsert of "+(flen*max)+" done in: " + tot + "ms, "+per+"ms per insert");
   d = new Date();
   updateCounts();
   tot = new Date() - d;
   per = tot/n;
   print("updateCounts "+ n +" times done in: " + tot + "ms, "+per+"ms per update");
   print("explain find({filter:\"abcd\"}).sort({count:-1}): ");
   printInterestingStats(db.test9.find({filter:"abcd"}).sort({count:-1}).explain());
   print("explain find({filter:\"abcd\"}).limit(100).sort({count:-1}): ");
   printInterestingStats(db.test9.find({filter:"abcd"}).limit(100).sort({count:-1}).explain());
}