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When upgrading a Content DB from Sharepoint 2016 to Sharepoint 2019 fails with following error message

Microsoft.SharePoint.Upgrade.SPUpgradeException: An extension defined in the database is not registered with the farm.   

 

at Microsoft.SharePoint.Administration.SPContentDatabaseExtensionValidator.LogAndThrowIfNotSubset(IEnumerable`1 farmExtensionTypes, SPContentDatabaseExtensionCollection databaseExtensions)   

 

at Microsoft.SharePoint.Administration.SPContentDatabaseExtensionValidator.VerifyDatabaseCompatibility(SPContentDatabase database)   

 

at Microsoft.SharePoint.Administration.SPContentDatabaseCollection.Add(SPContentDatabase database, Boolean provision, Guid webApplicationLockId, Int32 addFlags)   

 

at Microsoft.SharePoint.Administration.SPContentDatabaseCollection.Add(Guid newDatabaseId, String strDatabaseServer, String strDatabaseName, String strDatabaseUsername, String strDatabasePassword, String strDatabaseFailOverServer, Int32 warningSiteCount, Int32 maximumSiteCount, Int32 status, Boolean provision, Guid lockId, Int32 addFlags)   

 

at Microsoft.SharePoint.Administration.SPWebApplication.AddContentDatabase(SPWebApplication application, String strDatabaseServer, String strDatabase, String strDatabaseUser, String strDatabasePassword, String strDatabaseFailOverServer, Int32 cSiteWarning, Int32 cSiteLimit, Boolean bAssignDatabaseId, Int32 iAddFlags)   

 

at Microsoft.SharePoint.PowerShell.SPCmdletNewContentDatabase.InternalProcessRecord()   

 

at Microsoft.SharePoint.PowerShell.SPCmdlet.ProcessRecord()

 

The ULS Log clearly shows 

 

PowerShell.exe (0x2478)	0x2EFC	SharePoint Foundation	Database Extensions	aopbd	Medium	Ensuring farm m_extensions.
PowerShell.exe (0x2478)	0x2EFC	SharePoint Foundation	Database Extensions	aopbe	Medium	Ensuring database m_extensions.
PowerShell.exe (0x2478)	0x2EFC	SharePoint Foundation	Database Extensions	aopa1	Verbose	m_extensions is already initialized
PowerShell.exe (0x2478)	0x2EFC	SharePoint Foundation	Database Extensions	aopa1	Verbose	m_extensions is already initialized
PowerShell.exe (0x2478)	0x2EFC	SharePoint Foundation	Database Extensions	aopbi	High	The m_extensions of the database were not a subset of the m_extensions of the farm.
PowerShell.exe (0x2478)	0x2EFC	SharePoint Foundation	Database Extensions	aopbk	High	farm extension: System.RuntimeType
PowerShell.exe (0x2478)	0x2EFC	SharePoint Foundation	Database Extensions	aopa1	Verbose	m_extensions is already initialized
PowerShell.exe (0x2478)	0x2EFC	SharePoint Foundation	Database Extensions	aopbl	High	database extension: Microsoft.SharePoint.Administration.SPGlobalExtension, value 16.0.6.0, latestVersion 16.0.8.0
PowerShell.exe (0x2478)	0x2EFC	SharePoint Foundation	Database Extensions	aopbl	High	database extension: Microsoft.Office.Project.Server.Database.Extension.ProjectDatabaseExtension, value 16.1.310.0, latestVersion 17.0.288.0
PowerShell.exe (0x2478)	0x2EFC	SharePoint Foundation	Database Extensions	aopa1	Verbose	m_extensions is already initialized
PowerShell.exe (0x2478)	0x2EFC	SharePoint Foundation	Database Extensions	aq4ea	Medium	Calling extension method for SPGlobalExtension on object SPContentDatabase Name=SP19_Content.
PowerShell.exe (0x2478)	0x2EFC	SharePoint Foundation	Database Extensions	aq4ea	Medium	Calling extension method for ProjectDatabaseExtension on object SPContentDatabase Name=SP19_Content.

 

Compare the extensions registered and we can see project extension is missing.  here is how you can compare. 

$contentservice=[Microsoft.sharepoint.Administration.SPwebservice]::ContentService

$contentservice.RegisteredDatabaseExtensionTypes >>SP2016Farm_registered_Extn.txt

 

$contentservice=[Microsoft.sharepoint.Administration.SPwebservice]::ContentService

$contentservice.RegisteredDatabaseExtensionTypes >>SP2019Farm_registered_Extn.txt

 

 

Resolution:

Execute the following to register the missing extension

$svc = [Microsoft.SharePoint.Administration.SPWebService]::ContentService

[System.Reflection.Assembly]::LoadWithPartialName(“Microsoft.Office.Project.Server.Database.Extension”) | FL

$svc.RegisteredDatabaseExtensionTypes.EnsureAdded([Microsoft.Office.Project.Server.Database.Extension.ProjectDatabaseExtension])

$svc.Update($true)

The above is kindly provided by the Microsoft Tech Community!