Explain plan analysis (queryPlanner, executionStats) in MongoDB - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to get the explain plan for a MongoDB query.

MongoDB

db.collection.find({ age: { $gt: 25 } }).[1]()

Drag options to blanks, or click blank then click option'

AshowPlan

BexplainPlan

Cexplain

DqueryExplain

Attempts:

3 left

💡 Hint

Common Mistakes

Using a method name that does not exist like 'explainPlan'.

Trying to use 'showPlan' or 'queryExplain' which are not valid.

The explain() method returns the query plan and execution stats for a MongoDB query.

2fill in blank

medium

Complete the code to get the execution statistics from the explain output.

MongoDB

const result = db.collection.find({ status: 'active' }).explain();
const stats = result.[1];

Drag options to blanks, or click blank then click option'

AexecutionStats

BqueryPlanner

CplanSummary

DexecutionPlan

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'queryPlanner' which only shows the plan, not execution details.

Using 'planSummary' which is a brief summary, not detailed stats.

The executionStats field contains detailed information about how the query was executed, including execution time and number of documents examined.

3fill in blank

hard

Fix the error in accessing the winning plan from the explain output.

MongoDB

const plan = db.collection.find({}).explain().[1].winningPlan;

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AexecutionStats

BplanDetails

CexecutionPlan

DqueryPlanner

Attempts:

3 left

💡 Hint

Common Mistakes

Trying to get winningPlan from 'executionStats' which does not contain it.

Using non-existent fields like 'executionPlan' or 'planDetails'.

The winningPlan is inside the queryPlanner field of the explain output.

4fill in blank

hard

Fill both blanks to get the total number of documents examined and the number returned from execution stats.

MongoDB

const stats = db.collection.find({}).explain().[1];
const examined = stats.[2];

Drag options to blanks, or click blank then click option'

AexecutionStats

BqueryPlanner

CtotalDocsExamined

DnReturned

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'queryPlanner' instead of 'executionStats' for runtime data.

Using 'nReturned' instead of 'totalDocsExamined' for documents examined.

The executionStats field contains totalDocsExamined which shows how many documents MongoDB looked at during the query.

5fill in blank

hard

Fill all three blanks to get the number of documents returned, the execution time in milliseconds, and the stage name of the winning plan.

MongoDB

const explain = db.collection.find({}).explain();
const returned = explain.executionStats.[1];
const timeMs = explain.executionStats.[2];
const stage = explain.queryPlanner.winningPlan.[3];

Drag options to blanks, or click blank then click option'

AnReturned

BexecutionTimeMillis

Cstage

DtotalDocsExamined

Attempts:

3 left

💡 Hint

Common Mistakes

Mixing up fields between executionStats and queryPlanner.

Using 'totalDocsExamined' instead of 'nReturned' for returned documents.

nReturned is the number of documents returned, executionTimeMillis is the time taken, and stage is the name of the winning plan's root stage.