Getting ready

Assuming that you are already running a MongoDB server, we will be importing a dataset of around 100,000 records available in the form of a CSV file called chapter_2_mock_data.csv. You can download this file from the Packt website.

1. Import the sample data to the MongoDB server:

$mongoimport --headerline --ignoreBlanks --type=csv -d mydb -c mockdata -h localhost chapter_2_mock_data.csv

You should see output like this:

2017-06-18T08:25:08.444+0530    connected to: localhost
2017-06-18T08:25:09.498+0530 imported 100000 documents

1. Connect to the MongoDB instance and open a mongo shell:

mongo localhost:27017

1. Check that the documents are in the right place:

use mydb
db.mockdata.count()

You should see the following result:

105000

1. Let's fetch a document with the explain() method:

> db.mockdata.find({city:'Singapore'}).explain("executionStats")

You should see the following result:

{
    "executionStats": {
        "executionStages": {
            "advanced": 1,
            "direction": "forward",
            "docsExamined": 100000,
            "executionTimeMillisEstimate": 44,
            "filter": {
                "city": {
                    "$eq": "Singapore"
                }
            },
            "invalidates": 0,
            "isEOF": 1,
            "nReturned": 1,
            "needTime": 100000,
            "needYield": 0,
            "restoreState": 783,
            "saveState": 783,
            "stage": "COLLSCAN",
            "works": 100002
        },
        "executionSuccess": true,
        "executionTimeMillis": 41,
        "nReturned": 1,
        "totalDocsExamined": 100000,
        "totalKeysExamined": 0
    },
    "ok": 1,
    "queryPlanner": {
        "indexFilterSet": false,
        "namespace": "mydb.mockdata",
        "parsedQuery": {
            "city": {
                "$eq": "Singapore"
            }
        },
        "plannerVersion": 1,
        "rejectedPlans": [],
        "winningPlan": {
            "direction": "forward",
            "filter": {
                "city": {
                    "$eq": "Singapore"
                }
            },
            "stage": "COLLSCAN"
        }
    },
    "serverInfo": {
        "gitVersion": "888390515874a9debd1b6c5d36559ca86b44babd",
        "host": "vagrant-ubuntu-trusty-64",
        "port": 27017,
        "version": "3.4.4"
    }
}

1. Create an index on the city field:

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

The following result is obtained:

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

1. Execute the same fetch query:

> db.mockdata.find({city:'Singapore'}).explain("executionStats")

{
    "executionStats": {
        "executionStages": {
            "advanced": 1,
            "alreadyHasObj": 0,
            "docsExamined": 1,
            "executionTimeMillisEstimate": 0,
            "inputStage": {
                "advanced": 1,
                "direction": "forward",
                "dupsDropped": 0,
                "dupsTested": 0,
                "executionTimeMillisEstimate": 0,
                "indexBounds": {
                    "city": [
                        "[\"Singapore\", \"Singapore\"]"
                    ]
                },
                "indexName": "city_1",
                "indexVersion": 2,
                "invalidates": 0,
                "isEOF": 1,
                "isMultiKey": false,
                "isPartial": false,
                "isSparse": false,
                "isUnique": false,
                "keyPattern": {
                    "city": 1
                },
                "keysExamined": 1,
                "multiKeyPaths": {
                    "city": []
                },
                "nReturned": 1,
                "needTime": 0,
                "needYield": 0,
                "restoreState": 0,
                "saveState": 0,
                "seeks": 1,
                "seenInvalidated": 0,
                "stage": "IXSCAN",
                "works": 2
            },
            "invalidates": 0,
            "isEOF": 1,
            "nReturned": 1,
            "needTime": 0,
            "needYield": 0,
            "restoreState": 0,
            "saveState": 0,
            "stage": "FETCH",
            "works": 2
        },
        "executionSuccess": true,
        "executionTimeMillis": 0,
        "nReturned": 1,
        "totalDocsExamined": 1,
        "totalKeysExamined": 1
    },
    "ok": 1,
    "queryPlanner": {
        "indexFilterSet": false,
        "namespace": "mydb.mockdata",
        "parsedQuery": {
            "city": {
                "$eq": "Singapore"
            }
        },
        "plannerVersion": 1,
        "rejectedPlans": [],
        "winningPlan": {
            "inputStage": {
                "direction": "forward",
                "indexBounds": {
                    "city": [
                        "[\"Singapore\", \"Singapore\"]"
                    ]
                },
                "indexName": "city_1",
                "indexVersion": 2,
                "isMultiKey": false,
                "isPartial": false,
                "isSparse": false,
                "isUnique": false,
                "keyPattern": {
                    "city": 1
                },
                "multiKeyPaths": {
                    "city": []
                },
                "stage": "IXSCAN"
            },
            "stage": "FETCH"
        }
    },
    "serverInfo": {
        "gitVersion": "888390515874a9debd1b6c5d36559ca86b44babd",
        "host": "vagrant-ubuntu-trusty-64",
        "port": 27017,
        "version": "3.4.4"
    }
}