Description

Each Sitecore XP instance runs a schema synchronization task to ensure that it is using the latest Azure Search index schema for operations on the index. Schema synchronization occurs once per 20 seconds by default. If synchronization takes longer than 20 seconds to complete, the thread pool is forced to dispatch a new thread. If too many threads are created in such a way then no threads are left to handle HTTP requests. The issue is often accompanied by errors in the log files:

INFO Schema synchronization failed 
Exception: Sitecore.ContentSearch.Azure.Http.Exceptions.AzureSearchServiceRESTCallException 
Message: Error while search service call, see details in message 
Source: Sitecore.ContentSearch.Azure at Sitecore.ContentSearch.Azure.Http.SearchServiceClient.EnsureSuccessStatusCode(HttpResponseMessage response) 
at Sitecore.ContentSearch.Azure.Http.SearchServiceClient.GetIndex() 
at Sitecore.ContentSearch.Azure.Schema.SearchServiceSchemaSynchronizer.RefreshLocalSchema() 
at Sitecore.ContentSearch.Azure.Http.SearchService.SyncSchema(Object state) 
Nested Exception Exception: Sitecore.ContentSearch.Azure.Http.Exceptions.AzureSearchServiceRESTCallException 
Message: {"error":{"code":"","message":"You are sending too many requests. Please try again later."}}

Solution

To resolve the issue, consider one of the following options:

• Upgrade to Sitecore XP 9.2 Initial Release or higher (recommended).
• Download and install a patch compatible with the affected product version:
  https://github.com/SitecoreSupport/Sitecore.Support.229598/releases.