Question

While stress testing prototype of our brand new primary system, I run into concurrent issue with AppFabric Cache. When concurrently calling many DataCache.Get() and Put() with same cacheKey, where I attempt to store relatively large objet, I recieve “ErrorCode:SubStatus:There is a temporary failure. Please retry later.” It is reproducible by the following code:

        var dcfc = new DataCacheFactoryConfiguration
        {
            Servers = new[] {new DataCacheServerEndpoint("localhost", 22233)},
            SecurityProperties = new DataCacheSecurity(DataCacheSecurityMode.None, DataCacheProtectionLevel.None),
        };

        var dcf = new DataCacheFactory(dcfc);
        var dc = dcf.GetDefaultCache();

        const string key = "a";
        var value = new int [256 * 1024]; // 1MB

        for (int i = 0; i < 300; i++)
        {
            var putT = new Thread(() => dc.Put(key, value));
            putT.Start();               

            var getT = new Thread(() => dc.Get(key));
            getT.Start();
        }

When calling Get() with different key or DataCache is synchronized, this issue will not appear. If DataCache is obtained with each call from DataCacheFactory (DataCache is supposed to be thread-safe) or timeouts are prolonged it has no effect and error is still received.
It seems to me very strange that MS would leave such bug. Did anybody faced similar issue?

Answer 1

I also see the same behavior and my understanding is that this is by design. The cache contains two concurrency models:

• Optimistic Concurrency Model methods: Get, Put, …
• Pessimistic Concurrency Model: GetAndLock, PutAndLock, Unlock

If you use optimistic concurrency model methods like Get then you have to be ready to get DataCacheErrorCode.RetryLater and handle that appropriately – I also use a retry approach.

You might find more information at MSDN: Concurrency Models