Post configuring the User profile Service Application , You need to Start the Synchronization service if you intended to use ForeFront Identity Manager Component in Sharepoint 2010/2013 which provides abilities to Import / Export data from a variety of Directory sources & Augment profile data from Additional Sources like BCS etc. The sync service Startup has many known issues & bunch of issues which might cause the Sync Service startup failure .
This Post is to provide causes of Event ID 9i1w "ERR_Config_Db" as seen in ULS logs post trying to start the Sync Service
[Date and Time] OWSTIMER.EXE (0x1DA0) 0x1DA4 SharePoint Portal Server User Profiles 9i1w Medium ILM Configuration
ILM Configuration: Configuring database
ILM Configuration: Error 'ERR_CONFIG_DB'.
UserProfileApplication.SynchronizeMIIS: Failed to configure MIIS post database, will attempt during next rerun. Exception: System.Configuration.ConfigurationErrorsException: ERR_CONFIG_DB
at Microsoft.Office.Server.UserProfiles.Synchronization.ILMPostSetupConfiguration.ValidateConfigurationResult(UInt32 result)
at Microsoft.Office.Server.Administration.UserProfileApplication.SetupSynchronizationService(ProfileSynchronizationServiceInstance profileSyncInstance).
Note : Keep in mind for UPA Config db means Synchronization DB as all the configuration details is stored Here .
Possible Cause 1: This is due to insufficient privileges for the SharePoint Farm Account on the Sync DB (not the Config DB!). You need to add the farm account to the Sync DB users as DBO with a default schema of DBO and then start UPS again.
Possible Cause 2: Incorrect Pre-requisites installed , i.e SQL server Native Client 2012 /2014 is installed , while the Requirement is to have a SQL 2008 /2008 Sp1 . Details here : http://technet.microsoft.com/en-us/library/cc262485.aspx#reqOtherCap
Possible Cause 3: If you use SQL server 2014 to host the Sync DB or Moved your Databases to SQL 2014 ( Sharepoint 2013 ) , then there is a known issues & you need to Update to April 2014 CU or above for Sharepoint 2013 , https://support.microsoft.com/en-us/kb/2760265
Possible Cause 4: Connectivity issues to SQL server , like Wrong Alias . Start -->Run-->Cliconfg to check & configure aliases
Possible cause 5: Using FDQN of SQL server while creating the SharePoint server Farm instead of NetBIOS name .
Possible Cause 6: Triggers configured on the SQL server to disable adding new databases or modifications
Possible Cause 7: Auto Update statistics is disabled in SQL server
In SQL Management Studio, right-click on the Sync database, choose Properties, and click on the Options page. “Auto Update Statistics” is in the Automatic section, set the value to True