What does it mean when multiple queries try to modify the same data simultaneously without proper synchronization?

A situation where multiple requests simultaneously attempt to modify the same data without proper synchronization is called a race condition.

As a result of a race condition, the data state can become unpredictable or inconsistent, as operations may interrupt each other or overwrite changes.

To prevent such issues, synchronization mechanisms are used, for example:

• Locks (mutex, semaphores)
• Transactions in databases
• Use of atomic operations

An example in PHP using file locking:

$fp = fopen("lockfile.txt", "w+");
if (flock($fp, LOCK_EX)) { // exclusive lock
    // critical section: modify data
    // ...
    flock($fp, LOCK_UN); // release lock
}
fclose($fp);

This prevents simultaneous access to data and ensures the correctness of changes.