Check and set (CAS) operations are commonly used in Memcached to ensure that the cache value is only changed if it has not been altered since you last fetched it. This is useful in concurrent environments where multiple processes may be attempting to update the same key-value pair.
Here is an example of how to use CAS in Memcached with Ruby:
In this example, we're setting a key-value pair, then we're trying to update it using the
cas method. The block passed to
cas receives the current value, modifies it, and its return value will be stored back in Memcached. If the value has been changed by another process after we fetched it but before we could store the new value, a
Memcached::NotStored exception is raised.
casblock to minimize the chance of conflicts.
Memcached::NotStoredexception, leading to silent failures.
Q: Can I perform other operations inside the
A: Yes, you can perform any operation inside the
cas block. However, ensure these operations are quick to minimize the chance of another process changing the value before you can store your changes.
Q: What happens if two processes try to update the same key simultaneously?
A: If two processes try to update the same key simultaneously using
cas, one of them will get a
Memcached::NotStored exception. The one that gets the exception should handle it and decide what to do next.