MongoDB Index Checker Usage

This guide explains how to set up and use a Python script to check if your MongoDB queries are using indexes.

Prerequisites

• Python 3.x
• pymongo library
• MongoDB instance

Installation

1. Install Python:

   • Download and install Python from python.org.

2. Install pymongo:

   • You can install the pymongo library using pip:

     pip install pymongo

Setup

1. MongoDB Connection:

   • Ensure your MongoDB instance is running and accessible.
   • Insert dummy data + add index on some field's
   • Replace the MONGO_URI, DATABASE_NAME, and COLLECTION_NAME in the script with your MongoDB details.

2. Create queries.txt:

   • Create a file named queries.txt in the same directory as your script.
   • Add your MongoDB queries in JSON format, one per line. For example:

     {"name": "john"}
     {"age": {"$gte": 25}}
     {"city": "New York"}

Script

1. Script Code:

   • Copy the following script and save it as check_indexes.py:

     from pymongo import MongoClient
     import json
     
     # Replace these with your connection details
     MONGO_URI = "mongodb://localhost:27017/"
     DATABASE_NAME = "test_db"
     COLLECTION_NAME = "users"
     
     client = MongoClient(MONGO_URI)
     db = client[DATABASE_NAME]
     collection = db[COLLECTION_NAME]
     
     with open("queries.txt", "r") as f:
         queries = [json.loads(line.strip()) for line in f]
     
     for query in queries:
         # Explain the query and get the explain string
         explain_result = collection.find(query).explain()
         explain_string = str(explain_result)
     
         # Check for index usage and print results
         if "IXSCAN" in explain_string:
             print(f"Query: {query}")
             print("  Index likely used! 🎉")
         else:
             print(f"Query: {query}")
             print("  No clear indication of index usage. 🤔")
     
     client.close()

2. queries.txt:

   • Copy the following text and save it as queries.txt:

     {"order_date": { "$gt": "2023-10-31" }}
     {"name": "john"}
     {"email": "janedoe@example.com"}

Usage

1. Run the Script:

   • Open a terminal and navigate to the directory where your script is located.
   • Run the script using Python:

     python3 run-check.py

2. Output:

   • The script will output whether each query in queries.txt likely used an index or not. For example:

     Query: {'name': 'john'}
       Index likely used! 🎉
     Query: {'age': {'$gte': 25}}
       No clear indication of index usage. 🤔
     

Troubleshooting

• Connection Issues:

  • Ensure your MongoDB instance is running and the MONGO_URI is correct.
  • Check for network issues or firewall rules that might block the connection.

• Invalid Queries:

  • Ensure each line in queries.txt is a valid JSON object.

• Library Installation:

  • If you encounter issues with pymongo installation, ensure your Python and pip versions are compatible.

Further Enhancements

• Detailed Analysis:

  • Modify the script to parse the explain dictionary for more detailed analysis instead of converting it to a string.

• Error Handling:

  • Add try-except blocks to handle potential errors in database connections and file operations.

By following this guide, you should be able to set up and use the script to check if your MongoDB queries are using indexes effectively.