Frequent timeout errors with session state provider

[JLRishe]

I am using the Redis session state provider with an ASP.NET Azure App Service. I'm using Azure Cache for Redis for the cache.

Last week, I had a look at my app's logs, and noticed that I was getting several dozen Redis timeout errors per day. I have had issues in the past where Redis timeouts brought my app to a complete standstill, but that doesn't seem to be happening now. The timeouts occur sporadically but don't cause a critical disruption.

Service levels:

• App Service: Standard S1
• Redis: P1. I was using C2 until Friday, but the upgrade doesn't seem to have made a difference.

Today, I tried increasing the operation timeout value from 1000ms to 2000ms, but I am continuing to see about a dozen timeouts per hour.

Below is the error message and stack trace from one of these timeouts. What can I do to figure why these are happening and how to remedy them?

StackExchange.Redis.RedisTimeoutException: Timeout performing EVAL (2000ms), next: EVAL, inst: 12, qu: 0, qs: 0, aw: False, bw: Inactive, rs: ReadAsync, ws: Idle, in: 0, last-in: 0, cur-in: 0, sync-ops: 392, async-ops: 1, serverEndpoint: *************:6380, conn-sec: 396.97, mc: 1/1/0, mgr: 10 of 10 available, clientName: *******************(SE.Redis-v2.6.90.64945), IOCP: (Busy=0,Free=1000,Min=1,Max=1000), WORKER: (Busy=3,Free=8188,Min=1,Max=8191), v: 2.6.90.64945 (Please take a look at this article for some common client-side issues that can cause timeouts: https://stackexchange.github.io/StackExchange.Redis/Timeouts)
	Stack Trace:    at StackExchange.Redis.ConnectionMultiplexer.ExecuteSyncImpl[T](Message message, ResultProcessor`1 processor, ServerEndPoint server, T defaultValue) in /_/src/StackExchange.Redis/ConnectionMultiplexer.cs:line 1980
   at StackExchange.Redis.RedisBase.ExecuteSync[T](Message message, ResultProcessor`1 processor, ServerEndPoint server, T defaultValue) in /_/src/StackExchange.Redis/RedisBase.cs:line 62
   at StackExchange.Redis.RedisDatabase.ScriptEvaluate(String script, RedisKey[] keys, RedisValue[] values, CommandFlags flags) in /_/src/StackExchange.Redis/RedisDatabase.cs:line 1520
   at Microsoft.Web.Redis.StackExchangeClientConnection.<>c__DisplayClass7_0.<Eval>b__0() in C:\TeamCity\buildAgent\work\59b31e8e4035fd30\src\Shared\StackExchangeClientConnection.cs:line 68
   at Microsoft.Web.Redis.StackExchangeClientConnection.OperationExecutor(Func`1 redisOperation) in C:\TeamCity\buildAgent\work\59b31e8e4035fd30\src\Shared\StackExchangeClientConnection.cs:line 95
   at Microsoft.Web.Redis.StackExchangeClientConnection.RetryLogic(Func`1 redisOperation) in C:\TeamCity\buildAgent\work\59b31e8e4035fd30\src\Shared\StackExchangeClientConnection.cs:line 118
   at Microsoft.Web.Redis.StackExchangeClientConnection.Eval(String script, String[] keyArgs, Object[] valueArgs) in C:\TeamCity\buildAgent\work\59b31e8e4035fd30\src\Shared\StackExchangeClientConnection.cs:line 68
   at Microsoft.Web.Redis.RedisConnectionWrapper.TryTakeWriteLockAndGetData(DateTime lockTime, Int32 lockTimeout, Object& lockId, ISessionStateItemCollection& data, Int32& sessionTimeout) in C:\TeamCity\buildAgent\work\59b31e8e4035fd30\src\RedisSessionStateProvider\RedisConnectionWrapper.cs:line 184
   at Microsoft.Web.Redis.RedisSessionStateProvider.GetItemFromSessionStore(Boolean isWriteLockRequired, HttpContextBase context, String id, CancellationToken cancellationToken, Boolean& locked, TimeSpan& lockAge, Object& lockId, SessionStateActions& actions) in C:\TeamCity\buildAgent\work\59b31e8e4035fd30\src\RedisSessionStateProvider\RedisSessionStateProvider.cs:line 291
   at Microsoft.Web.Redis.RedisSessionStateProvider.<GetItemExclusiveAsync>d__20.MoveNext() in C:\TeamCity\buildAgent\work\59b31e8e4035fd30\src\RedisSessionStateProvider\RedisSessionStateProvider.cs:line 206
--- End of stack trace from previous location where exception was thrown ---
   at System.Runtime.CompilerServices.TaskAwaiter.ThrowForNonSuccess(Task task)
   at System.Runtime.CompilerServices.TaskAwaiter.HandleNonSuccessAndDebuggerNotification(Task task)
   at Microsoft.AspNet.SessionState.SessionStateModuleAsync.<GetSessionStateItemAsync>d__74.MoveNext()
--- End of stack trace from previous location where exception was thrown ---
   at System.Runtime.CompilerServices.TaskAwaiter.ThrowForNonSuccess(Task task)
   at System.Runtime.CompilerServices.TaskAwaiter.HandleNonSuccessAndDebuggerNotification(Task task)
   at Microsoft.AspNet.SessionState.SessionStateModuleAsync.<AcquireStateAsync>d__65.MoveNext()
--- End of stack trace from previous location where exception was thrown ---
   at System.Runtime.CompilerServices.TaskAwaiter.ThrowForNonSuccess(Task task)
   at System.Runtime.CompilerServices.TaskAwaiter.HandleNonSuccessAndDebuggerNotification(Task task)
   at Microsoft.AspNet.SessionState.TaskAsyncHelper.EndTask(IAsyncResult ar)
   at Microsoft.AspNet.SessionState.SessionStateModuleAsync.EndAcquireState(IAsyncResult result)
   at System.Web.HttpApplication.AsyncEventExecutionStep.InvokeEndHandler(IAsyncResult ar)
   at System.Web.HttpApplication.AsyncEventExecutionStep.OnAsyncEventCompletion(IAsyncResult ar)

[rubberduck203]

@JLRishe did you ever find a cause or solution?