SharePoint error from ULS logs

Question

We had couple of workflow failed at a point of time when we gone through the ULS logs we found below error. Not sure, why it occurred, what does it mean? We didnt do any patching at that time.

`
01/18/2019 12:08:06.77 powershell (0x4264) 0x36F4 SharePoint Foundation Upgrade SPUpgradeSession ajxmj ERROR   
 at System.Data.ProviderBase.DbConnectionPool.TryGetConnection(DbConnection owningObject, UInt32 waitForMultipleObjectsTimeout, Boolean allowCreate, Boolean onlyOneCheckConnection, DbConnectionOptions userOptions, DbConnectionInternal& connection)    
 at System.Data.ProviderBase.DbConnectionPool.TryGetConnection(DbConnection owningObject, TaskCompletionSource`1 retry, DbConnectionOptions userOptions, DbConnectionInternal& connection)    
 at System.Data.ProviderBase.DbConnectionFactory.TryGetConnection(DbConnection owningConnection, TaskCompletionSource`1 retry, DbConnectionOptions userOptions, DbConnectionInternal oldConnection, DbConnectionInternal& connection)    
 at System.Data.ProviderBase.DbConnectionInternal.TryOpenConnectionInternal(DbConnection outerConnection, DbConnectionFactory connectionFactory, TaskCompletionSource`1 retry, DbConnectionOptions userOptions)    
 at System.Data.SqlClient.SqlConnection.TryOpenInner(TaskCompletionSource`1 retry)    
 at System.Data.SqlClient.SqlConnection.TryOpen(TaskCompletionSource`1 retry)    
 at System.Data.SqlClient.SqlConnection.Open()    
 at Microsoft.SharePoint.Utilities.SqlSession.OpenConnection()    
 at Microsoft.SharePoint.Utilities.SqlSession.ExecuteReader(SqlCommand command, CommandBehavior behavior, SqlQueryData monitoringData, Boolean retryForDeadLock)    
 at Microsoft.SharePoint.Utilities.SqlSession.ExecuteReader(SqlCommand command, Boolean retryForDeadLock)    
 at Microsoft.SharePoint.Utilities.SqlSession.ExecuteReader(SqlCommand command)    
 at Microsoft.SharePoint.Upgrade.SPDatabaseSequence.GetVersion(SPDatabase database, Guid id, Version defaultVersion, SqlSession session, SPDatabaseSequence sequence)    
 at Microsoft.SharePoint.Upgrade.SPDatabaseSequence.get_SchemaVersion()    
 at Microsoft.SharePoint.Upgrade.SPSequence.get_IsBackwardsCompatible()    
 at Microsoft.SharePoint.Upgrade.SPUpgradeSession.IsBackwardsCompatible(Object o, Boolean bRecurse) 00000000-0000-0000-0000-000000000000

`

Answer 1

It looks like it was SPproduct Job, which running really often. This error looks like it cannot connect to the SQL instance at this moment. You can check Failed Jobs in Monitoring in Central Administration. But probably its false positive for you.

You need to learn that SharePoint generating lots of errors, but there are really a few amount which are causing some problems in environment.