Why Are My Repeated MySQL Queries Not Returning the Latest Data?

Repeated MySQL Queries Not Returning Latest Data: Resolving the Issue Through Transaction Commit

In Python, while repeatedly querying a rapidly changing MySQL database, it's crucial to ensure that each query retrieves the most up-to-date data. However, some may encounter the issue where subsequent queries return identical data despite the database undergoing changes. This is due to the underlying isolation level of the database connection.

The concept of isolation levels dictates how transactions are isolated from each other. In the case of MySQL's default isolation level, REPEATABLE READ, each query within the same transaction relies on a snapshot of the database taken at the start of the transaction. This means that subsequent queries will not reflect any database changes made while the transaction was active.

To resolve this issue, it is essential to commit the connection after each query. This initiates a new transaction and ensures that the next query operates on the latest database snapshot. Here's an example:

<code class="python">while True:
    # SQL query
    sql = "SELECT * FROM table"

    # Read the database, store as a dictionary
    mycursor = mydb.cursor(dictionary=True)
    mycursor.execute(sql)

    # Store data in rows
    myresult = mycursor.fetchall()

    # Transfer data into list
    for row in myresult:
        myList[int(row["rowID"])] = (row["a"], row["b"], row["c"])

        print(myList[int(row["rowID"])])

    # Commit !
    mydb.commit()
    print("---")
    sleep (0.1)</code>

By committing after each query, the connection established a new transaction, ensuring that each subsequent query would read the most recent database snapshot, thereby reflecting the latest database changes. This solves the problem of repeated queries consistently returning outdated data.

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