If you use search on your Sharepoint site you may face with the issue that search crawler stuck in Crawling full status. In the logs you may find the following error:
Failed to create session with indexer ---> Microsoft.Ceres.SearchCore.Services.ContentRouter.ContentException: Unable to connect to index system
In this case try to execute the following PowerShell cmdlets:
$ssa = Get-SPEnterpriseSearchServiceApplication Get-SPEnterpriseSearchStatus -Text -SearchApplication $ssa
It should show all components of search topology in Active state:
If there will be components which state is Degraded – your topology is in wrong state. In this case solution is to recreation of Search service application. After that run full crawl and it should work and stop successfully this time.