text: 
  t = db.mr1;
  t.drop();
  
  t.save( { x : 1 , tags : [ "a" , "b" ] } );
  t.save( { x : 2 , tags : [ "b" , "c" ] } );
  t.save( { x : 3 , tags : [ "c" , "a" ] } );
  t.save( { x : 4 , tags : [ "b" , "c" ] } );
  
  emit = printjson;
  
  function d( x ){
      printjson( x );
  }
  
  ks = "_id";
  if ( db.version() == "1.1.1" )
      ks = "key";
  
  
  m = function(){
      this.tags.forEach(
          function(z){
              emit( z , { count : 1 } );
          }
      );
  };
  
  m2 = function(){
      for ( var i=0; i<this.tags.length; i++ ){
          emit( this.tags[i] , 1 );
      }
  };
  
  
  r = function( key , values ){
      var total = 0;
      for ( var i=0; i<values.length; i++ ){
          total += values[i].count;
      }
      return { count : total };
  };
  
  r2 = function( key , values ){
      var total = 0;
      for ( var i=0; i<values.length; i++ ){
          total += values[i];
      }
      return total;
  };
  
  res = db.runCommand( { mapreduce : "mr1" , map : m , reduce : r , out : "mr1_out" } );
  d( res );
  if ( ks == "_id" ) assert( res.ok , "not ok" );
  assert.eq( 4 , res.counts.input , "A" );
  x = db[res.result];
  
  assert.eq( 3 , x.find().count() , "B" );
  x.find().forEach( d );
  z = {};
  x.find().forEach( function(a){ z[a[ks]] = a.value.count; } );
  d( z );
  assert.eq( 3 , Object.keySet( z ).length , "C" );
  assert.eq( 2 , z.a , "D" );
  assert.eq( 3 , z.b , "E" );
  assert.eq( 3 , z.c , "F" );
  x.drop();
  
  res = db.runCommand( { mapreduce : "mr1" , map : m , reduce : r , query : { x : { "$gt" : 2 } } , out : "mr1_out" } );
  d( res );
  assert.eq( 2 , res.counts.input , "B" );
  x = db[res.result];
  z = {};
  x.find().forEach( function(a){ z[a[ks]] = a.value.count; } );
  assert.eq( 1 , z.a , "C1" );
  assert.eq( 1 , z.b , "C2" );
  assert.eq( 2 , z.c , "C3" );
  x.drop();
  
  res = db.runCommand( { mapreduce : "mr1" , map : m2 , reduce : r2 , query : { x : { "$gt" : 2 } } , out : "mr1_out" } );
  d( res );
  assert.eq( 2 , res.counts.input , "B" );
  x = db[res.result];
  z = {};
  x.find().forEach( function(a){ z[a[ks]] = a.value; } );
  assert.eq( 1 , z.a , "C1z" );
  assert.eq( 1 , z.b , "C2z" );
  assert.eq( 2 , z.c , "C3z" );
  x.drop();
  
  res = db.runCommand( { mapreduce : "mr1" , out : "mr1_foo" , map : m , reduce : r , query : { x : { "$gt" : 2 } } } );
  d( res );
  assert.eq( 2 , res.counts.input , "B2" );
  assert.eq( "mr1_foo" , res.result , "B2-c" );
  x = db[res.result];
  z = {};
  x.find().forEach( function(a){ z[a[ks]] = a.value.count; } );
  assert.eq( 1 , z.a , "C1a" );
  assert.eq( 1 , z.b , "C2a" );
  assert.eq( 2 , z.c , "C3a" );
  x.drop();
  
  for ( i=5; i<1000; i++ ){
      t.save( { x : i , tags : [ "b" , "d" ] } );
  }
  
  res = db.runCommand( { mapreduce : "mr1" , map : m , reduce : r , out : "mr1_out" } );
  d( res );
  assert.eq( 999 , res.counts.input , "Z1" );
  x = db[res.result];
  x.find().forEach( d )
  assert.eq( 4 , x.find().count() , "Z2" );
  assert.eq( "a,b,c,d" , x.distinct( ks ) , "Z3" );
  
  function getk( k ){
      var o = {};
      o[ks] = k;
      return x.findOne( o );
  }
  
  assert.eq( 2 , getk( "a" ).value.count , "ZA" );
  assert.eq( 998 , getk( "b" ).value.count , "ZB" );
  assert.eq( 3 , getk( "c" ).value.count , "ZC" );
  assert.eq( 995 , getk( "d" ).value.count , "ZD" );
  x.drop();
  
  if ( true ){
      printjson( db.runCommand( { mapreduce : "mr1" , map : m , reduce : r , verbose : true , out : "mr1_out" } ) );
  }
  
  print( "t1: " + Date.timeFunc( 
      function(){
          var out = db.runCommand( { mapreduce : "mr1" , map : m , reduce : r , out : "mr1_out" } );
          if ( ks == "_id" ) assert( out.ok , "XXX : " + tojson( out ) );
          db[out.result].drop();
      } , 10 ) + " (~500 on 2.8ghz) - itcount: " + Date.timeFunc( function(){ db.mr1.find().itcount(); } , 10 ) );    
  
  
  
  // test doesn't exist
  res = db.runCommand( { mapreduce : "lasjdlasjdlasjdjasldjalsdj12e" , map : m , reduce : r , out : "mr1_out" } );
  assert( ! res.ok , "should be not ok" );
  
  if ( true ){
      correct = {};
      
      for ( i=0; i<20000; i++ ){
          k = "Z" + i % 10000;
          if ( correct[k] )
              correct[k]++;
          else
              correct[k] = 1;
          t.save( { x : i , tags : [ k ] } );
      }
      
      res = db.runCommand( { mapreduce : "mr1" , out : "mr1_foo" , map : m , reduce : r } );
      d( res );
      print( "t2: " + res.timeMillis + " (~3500 on 2.8ghz) - itcount: " + Date.timeFunc( function(){ db.mr1.find().itcount(); } ) );
      x = db[res.result];
      z = {};
      x.find().forEach( function(a){ z[a[ks]] = a.value.count; } );
      for ( zz in z ){
          if ( zz.indexOf( "Z" ) == 0 ){
              assert.eq( correct[zz] , z[zz] , "ZZ : " + zz );
          }
      }
      x.drop();
      
      res = db.runCommand( { mapreduce : "mr1" , out : "mr1_foo" , map : m2 , reduce : r2 , out : "mr1_out" } );
      d(res);
      print( "t3: " + res.timeMillis + " (~3500 on 2.8ghz)" );
  
      res = db.runCommand( { mapreduce : "mr1" , map : m2 , reduce : r2 , out : { inline : true } } );
      print( "t4: " + res.timeMillis  );
  
  }
  
  
  res = db.runCommand( { mapreduce : "mr1" , map : m , reduce : r , out : "mr1_out" } );
  assert( res.ok , "should be ok" );
  
  t.drop();
  t1 = db.mr1_out;
  t1.drop();