Records : 4716225 ( ~5 million records )
Size on disk : ~ 500 MB

db.flights.stats()

Execution Time: 1 ms



 GroupAggregate  (cost=40.69..7646.54 rows=1 width=8) (actual time=0.743..0.743 rows=1 loops=1)
Output: flightnum, count(*)
 ->  Bitmap Heap Scan on public.flights  (cost=40.69..7638.85 rows=1535 width=8) (actual     time=0.179..0.594 rows=382 loops=1)
    Output: id, year, month, dayofmonth, dayofweek, deptime, crsdeptime, arrtime, crsarrtime, uniquecarrier, flightnum, tailnum, actualelapsedtime, crselapsedtime, airtime, arrdelay, depdelay, origin, dest, distance, taxiin, taxiout, cancelled, cancell (...)
    Recheck Cond: (flights.flightnum = 1489)
    Filter: ((flights.year >= 1987) AND (flights.dayofweek >= 1) AND (flights.dayofweek <= 5))
    Rows Removed by Filter: 158
    ->  Bitmap Index Scan on flightnum_index  (cost=0.00..40.31 rows=2117 width=0) (actual time=0.160..0.160 rows=540 loops=1)
          Index Cond: (flights.flightnum = 1489)

db.flights.group({key: {"FlightNum": 1},cond: {"Year": {$gte:1987}, "DayOfWeek": {$gte:1, $lte:5}, "FlightNum": 1489},reduce: function(curr, result){ result.total +=1 },initial:{total:0}})

Execution Time:  20 ms

db.flights.mapReduce(
function() { emit(this.FlightNum, this.total); },
function(key, values) { return values+1 },
{
query: {"Year": {$gte:1987}, "DayOfWeek": {$gte:1, $lte:5}, "FlightNum": 1489 },
 out: "total"
}
)

{

"result" : "total",
"timeMillis" : 152,     <——
"counts" : {
    "input" : 382,
    "emit" : 382,
    "reduce" : 4,
    "output" : 1
},
"ok" : 1,
}


Execution Time:  152 ms