If you are upgrading to TFS 2015 there is a very tiny chance you might hit this error:
[19:40:39.780] System.Data.SqlClient.SqlException (0x80131904): The CREATE UNIQUE INDEX statement terminated because a duplicate key was found for the object name ‘dbo.tbl_Workspace_Dataspace’ and the index name ‘IX_tbl_OwnerId_WorkspaceName_WorkspaceVersion_Type’. The duplicate key value is (1, <GUID>, <WorkspaceName>, 1, 0).
[19:40:39.780] Rebuilding index: IX_tbl_OwnerId_WorkspaceName_WorkspaceVersion_Type
[19:40:39.780] ALTER INDEX [IX_tbl_OwnerId_WorkspaceName_WorkspaceVersion_Type] ON [dbo].[tbl_Workspace_Dataspace] REBUILD WITH(ONLINE=OFF, MAXDOP=0)
The workaround is to run the follow SQL Script on the TFS Collection database that failed to upgrade and then restart the upgrade job.
DECLARE @fallbackId AS INT
@fallbackTfId = vcim.TeamFoundationId,
@fallbackId = vcim.IdentityId
FROM tbl_VCIdentityMap vcim
WHERE PartitionId = 1
ORDER BY vcim.IdentityId ASC
SET WorkspaceName = SUBSTRING(wd.WorkspaceName, 1, 54) + ‘_TF’ + SUBSTRING(CONVERT(NVARCHAR(36), NEWID()), 1, 7)
FROM tbl_Workspace_Dataspace wd
JOIN tbl_Workspace w
ON w.PartitionId = wd.PartitionId
AND w.WorkspaceId = wd.WorkspaceId
AND w.OwnerId <> @fallbackId
WHERE wd.PartitionId = 1
AND wd.OwnerId = @fallbackTfId
AND wd.WorkspaceName = w.WorkspaceName