Sitecore Redis Timeout Exception on ZADD Shared_ExpirationIndex

Question

We are using Sitecore 9.3 in our multi-site application. And we are using Redis Cache in one of our application. We are suddenly facing the below exception in our Redis server. Please find the below exception details:

Exception: StackExchange.Redis.RedisTimeoutException
Message: Timeout performing ZADD shared_ExpirationIndex (5000ms), inst: 9, qs: 6, in: 0, serverEndpoint: Unspecified/XXX.redis.cache.windows.net:6390, mgr: 10 of 10 available, clientName: XXX, IOCP: (Busy=0,Free=1000,Min=8,Max=1000), WORKER: (Busy=21,Free=32746,Min=8,Max=32767), v: 2.0.519.65453 (Please take a look at this article for some common client-side issues that can cause timeouts: https://stackexchange.github.io/StackExchange.Redis/Timeouts)
Source: StackExchange.Redis

Below is the code used to set the redis cache value:

            var cache = Connection.GetDatabase();
            var serializedModel = JsonConvert.SerializeObject(model);
            var cachedValue = expirationInMinutes != 0 
                ? cache.StringSet(cacheKeyName, serializedModel, TimeSpan.FromMinutes(expirationInMinutes))
                : cache.StringSet(cacheKeyName, serializedModel);

Please suggest the reason for this timeout exception.

Answer 1

I have faced a similer type of issue, could you please check the following:

• In the Web.config and Sitecore.Analytics.Tracking.config files, increase the pollingInterval attribute value on both Private and Shared session state provider definitions from 2 to 60 seconds.
• In the Sitecore.Analytics.Tracking.config file, find the timeoutBetweenLockAttempts parameter. Increase its value from 10 to 200 milliseconds.

Review your config files from your CD server according to Sitecore recommendation in this KB article here https://support.sitecore.com/kb?id=kb_article_view&sysparm_article=KB0858026

I also recommend you check if the cache tuning is enough or not.

• Cache Tunning in Sitecore
• Monitor and Tune the Cache on the CD Server
• IsLanguageFallbackValid Field Cache Tunning in Sitecore

If your problem still persists then (ensure that you are not customizing the Redis):

• Ensure CPU usage is not high. This is a limitation from StackExchange.Redis.
• Increase operationTimeoutInMilliseconds from 5000 ms to higher. https://support.sitecore.com/kb?id=kb_article_view&sysparm_article=KB0464570
• Scale your Redis

See the Blog Post for more details: Intermittent StackExchange.Redis.RedisTimeout Exception in Sitecore