[Mongodb] M-102 Week 3 Assignments

-- 3.1

db.sensor_readings.find( {   tstamp : {      $gte : ISODate("2012-08-01"),      $lte :  ISODate("2012-09-01")    },   active : true } ).limit(3).explain()
{
 "cursor" : "BasicCursor",
 "isMultiKey" : false,
 "n" : 3,
 "nscannedObjects" : 2696,
 "nscanned" : 2696,
 "nscannedObjectsAllPlans" : 2696,
 "nscannedAllPlans" : 2696,
 "scanAndOrder" : false,
 "indexOnly" : false,
 "nYields" : 0,
 "nChunkSkips" : 0,
 "millis" : 6,
 "indexBounds" : {
 
 },
 "server" : "cmo3233:27017"
}

> db.sensor_readings.ensureIndex({tstamp:1, active:1})
> db.sensor_readings.find( {   tstamp : {      $gte : ISODate("2012-08-01"),      $lte :  ISODate("2012-09-01")    },   active : true } ).limit(3).explain()
{
 "cursor" : "BtreeCursor tstamp_1_active_1",
 "isMultiKey" : false,
 "n" : 3,
 "nscannedObjects" : 3,
 "nscanned" : 5,
 "nscannedObjectsAllPlans" : 7,
 "nscannedAllPlans" : 9,
 "scanAndOrder" : false,
 "indexOnly" : false,
 "nYields" : 0,
 "nChunkSkips" : 0,
 "millis" : 0,
 "indexBounds" : {
  "tstamp" : [
   [
    ISODate("2012-08-01T00:00:00Z"),
    ISODate("2012-09-01T00:00:00Z")
   ]
  ],
  "active" : [
   [
    true,
    true
   ]
  ]
 },
 "server" : "cmo3233:27017"
}
============
> homework.a()
That's good - you can submit the answer below (just submit the number).  however there
is an index you could
create that will get nscanned down to 3 for the query of interest. see if you can
do that or watch the answer video for details on that...
6
============
=> Second index de test
> db.sensor_readings.ensureIndex({active:1, str:1, tstamp:1, x:1})
---- 3.2 (currentOp / killOp)
> homework.c()
> 12
-- 3.3
> db.runCommand({compact : 'sensor_readings'})
> homework.d()
21