Get execution stats in MongoDB for a collection

To get execution stats in MongoDB for a collection, use the explain() method with "executionStats" parameter. This provides detailed performance information about query execution including execution time and documents examined.

Syntax

db.collection.find(query).explain("executionStats");

Sample Data

db.demo157.insertMany([
    {"Status": "Active"},
    {"Status": "InActive"}
]);

{
    "acknowledged": true,
    "insertedIds": [
        ObjectId("5e354fdffdf09dd6d08539fc"),
        ObjectId("5e354fe3fdf09dd6d08539fd")
    ]
}

Display all documents from the collection ?

db.demo157.find();

{ "_id": ObjectId("5e354fdffdf09dd6d08539fc"), "Status": "Active" }
{ "_id": ObjectId("5e354fe3fdf09dd6d08539fd"), "Status": "InActive" }

Example: Get Execution Stats

db.demo157.find({Status: { $in: ['Active','InActive'] }}).explain("executionStats");

{
    "queryPlanner": {
        "plannerVersion": 1,
        "namespace": "test.demo157",
        "indexFilterSet": false,
        "parsedQuery": {
            "Status": {
                "$in": [
                    "Active",
                    "InActive"
                ]
            }
        },
        "winningPlan": {
            "stage": "COLLSCAN",
            "filter": {
                "Status": {
                    "$in": [
                        "Active",
                        "InActive"
                    ]
                }
            },
            "direction": "forward"
        },
        "rejectedPlans": []
    },
    "executionStats": {
        "executionSuccess": true,
        "nReturned": 2,
        "executionTimeMillis": 18,
        "totalKeysExamined": 0,
        "totalDocsExamined": 2,
        "executionStages": {
            "stage": "COLLSCAN",
            "nReturned": 2,
            "executionTimeMillisEstimate": 0,
            "works": 4,
            "advanced": 2,
            "docsExamined": 2
        }
    },
    "ok": 1
}

Key Points

• executionTimeMillis: Total time taken to execute the query
• totalDocsExamined: Number of documents examined during execution
• nReturned: Number of documents returned by the query
• stage: Shows query execution method (COLLSCAN indicates collection scan)

Conclusion

The explain("executionStats") method provides comprehensive performance metrics for MongoDB queries. Use it to analyze query efficiency and identify optimization opportunities for better database performance.