Check-and-set (CAS) operation is used in Memcached to solve the problem of lost updates due to overwrites. A common use case for the 'csharp memcached cas' query would be when you need to perform a read-modify-write operation on data stored in Memcached using C#, ensuring that the data has not been modified by another client between the read and write operations.
Here is a simple example using the EnyimMemcached client for C#:
using Enyim.Caching; using Enyim.Caching.Memcached; // Create client MemcachedClient client = new MemcachedClient(); // Assume "Key1" already exists in cache CasResult<string> result = client.GetWithCas<string>("Key1"); // Check if we got the value successfully if (result.Result != null) { // Modify the value string newValue = result.Result + "_modified"; // Try to store it back using CAS CasResult<bool> setResult = client.Cas(StoreMode.Set, "Key1", newValue, result.Cas); if (!setResult.Result) { Console.WriteLine("The key was updated by someone else."); } }
In this code snippet, initially, we're getting a key-value pair with its CAS value using GetWithCas()
. If the key does exist, we modify the value, then try to update the key-value pair using Cas()
. If the update fails because another client updated the data, we output a message indicating so.
GetWithCas()
and Cas()
calls. In such cases, an exception won't be thrown; instead, the Result
property of the CasResult
will be false
.Q: What happens when a key is evicted from Memcached? Does its CAS value reset? A: Yes. When a key is evicted and then added again, it will have a new CAS value.
Q: Can I use CAS for transactions in Memcached? A: No. Memcached doesn't support transactions. CAS can help avoid overwrite conflicts, but it does not provide transactional integrity across multiple keys.
Dragonfly is fully compatible with the Redis ecosystem and requires no code changes to implement.