How to do it...

1. We begin by connecting to the mongo shell of the server and viewing all indexes on the system:

> db.mockdata.getIndexes()

The following result is obtained:

[
  {
    "v" : 2,
    "key" : {
      "_id" : 1
    },
    "name" : "_id_",
    "ns" : "mydb.mockdata"
  },
  {
    "v" : 2,
    "key" : {
      "city" : 1,
      "first_name" : 1
    },
    "name" : "city_1_first_name_1",
    "ns" : "mydb.mockdata"
  }
]

1. Execute a dropIndex() command to delete a particular index:

> db.mockdata.dropIndex('city_1_first_name_1')

You should see the following result:

{ "nIndexesWas" : 2, "ok" : 1 }

1. Let's recreate the index:

> db.mockdata.createIndex({'city':1}, {name: 'city_index'})

{
   "createdCollectionAutomatically" : false,
   "numIndexesBefore" : 1,
   "numIndexesAfter" : 2,
   "ok" : 1
}

1. Run getIndexes() to fetch all indexes of the collection:

> db.mockdata.getIndexes()

We should see the following result:

[
  {
    "v" : 2,
    "key" : {
      "_id" : 1
    },
    "name" : "_id_",
    "ns" : "mydb.mockdata"
  },
  {
    "v" : 2,
    "key" : {
      "city" : 1
    },
    "name" : "city_index",
    "ns" : "mydb.mockdata"
  }
]

1. Try creating the index again on the city field:

> db.mockdata.createIndex({'city':1})

You should see the following message:

{
  "createdCollectionAutomatically" : false,
   "numIndexesBefore" : 2,
   "numIndexesAfter" : 2,
   "note" : "all indexes already exist",
   "ok" : 1
}

1. Check the size of the index:

stats = db.mockdata.stats()
stats["totalIndexSize"]

It should show the following result:

1818624

1. Let us view the size of each index:

stats["indexSizes"]

This should show the following result:

{ "_id_" : 905216, "city_index" : 913408 }

1. Re-index city_index:

> db.mockdata.reIndex('city_index')

The following result is obtained:

{
  "nIndexesWas" : 2,
  "nIndexes" : 2,
  "indexes" : [
    {
      "v" : 2,
      "key" : {
        "_id" : 1
      },
      "name" : "_id_",
      "ns" : "mydb.mockdata"
    },
    {
      "v" : 2,
      "key" : {
        "city" : 1
      },
      "name" : "city_index",
      "ns" : "mydb.mockdata"
    }
  ],
  "ok" : 1
}