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Database Troubleshooting

This article covers common database-related issues in dab Nexus and their solutions.

Task Status Inconsistencies​

Symptoms​

  • Tasks remain in Running status although they have completed or failed
  • Task status does not match the actual state of the extraction
  • Runs show incorrect completion states
  • Scheduled Tasks fail intermittently without clear errors

Cause​

These symptoms typically occur when the Application Database and Extraction/Results databases share the same SQL Server instance. During large data extractions, the SQL Server experiences significant load. This can cause:

  1. Connection timeouts to the Application Database
  2. Write operations failing for task state updates
  3. Inconsistent status information stored in the Application Database

The Application Database stores all task states and must remain responsive at all times. When it competes for resources with heavy extraction workloads, connection stability suffers.

Diagnosis​

Check your SQL Server logs for:

  • Connection timeout errors
  • Deadlock warnings
  • Resource contention messages

Verify your current setup:

  • Are the Application Database and Extraction databases on the same SQL Server instance?
  • Does the problem occur during or after large extractions?

Solution​

Migrate the Application Database to a dedicated SQL Server instance. See the migration guide below.


Migrating the Application Database to a Separate Instance​

If you are experiencing task status inconsistencies or connection issues due to a shared SQL Server instance, follow these steps to migrate the Application Database to a dedicated instance.

Prerequisites​

  • New SQL Server instance provisioned (see System Requirements)
  • Administrative access to both SQL Server instances
  • dab Nexus service account credentials
  • Sufficient downtime window for the migration

Migration Steps​

1. Create Backups​

  • Create a full backup of the Application Database
  • Additionally backup all Data Databases (Extraction/Results)
  • All configuration data (Third-Party Services, SAP connections, user settings) is stored in the Application Database
Important

Do not skip the backup step. The Application Database contains all your dab Nexus configuration.

2. Stop the dab Nexus Service​

  • Open Windows Services (services.msc)
  • Stop the dab Nexus service
  • Verify the service has completely stopped before proceeding

3. Restore the Application Database to the New Instance​

  • Restore the Application Database backup to the new dedicated SQL Server instance
  • Ensure the database name remains the same, or note the new name for the configuration update
  • Verify the restore completed successfully

4. Adjust Configuration.json​

  • Navigate to the dab Nexus installation directory
  • Edit Configuration.json
  • Update the ApplicationDatabase connection string:
    • Server name: Update to the new instance
    • Database name: Update if renamed during restore
  • See Configuration.json Reference for connection string examples

Example connection string update:

"ConnectionStrings": {
  "ApplicationDatabase": "Server=NEW-SQL-INSTANCE;Database=NexusHome;Trusted_Connection=True;MultipleActiveResultSets=true"
}

5. Restart the dab Nexus Service​

  • Start the dab Nexus service
  • Check Windows Event Viewer for any startup errors
  • Verify successful startup by accessing the dab Nexus web interface

6. Create New SQL Connections in dab Nexus​

  • Log in to dab Nexus
  • Navigate to Settings > SQL Servers
  • Create new SQL connection(s) pointing to your Extraction/Results instance(s)
  • Test each connection before proceeding

7. Update Scheduled Tasks​

Review all Tasks that use SQL connections:

  • Deactivate Tasks with the old SQL connection (they will fail otherwise)
  • Clone each affected Task
  • Update the SQL connection in the cloned Task to use the new connection
  • Activate the new Task
  • Verify the Task runs successfully
  • Delete the old Task after verification
Note

Do not delete old Tasks until you have verified the cloned Tasks work correctly.

Post-Migration Verification​

  • Run a test extraction to verify connectivity to the Extraction database
  • Monitor Task statuses to confirm they update correctly
  • Check SQL Server logs on both instances for any connection issues
  • Verify scheduled Tasks execute as expected

Connection Timeout Errors​

Symptoms​

  • "Connection timeout" errors in dab Nexus logs
  • Tasks fail with database connection errors
  • Intermittent connectivity issues

Possible Causes​

  1. Network issues between dab Nexus and SQL Server
  2. SQL Server overloaded (shared instance problem)
  3. Firewall blocking connections
  4. SQL Server not configured for remote connections

Solutions​

  • Verify network connectivity using Test-NetConnection or telnet to SQL Server port (default: 1433)
  • Check SQL Server Configuration Manager for enabled protocols
  • Review firewall rules for SQL Server port
  • Consider migrating to separate instances if overload is the cause

Permission Errors​

Symptoms​

  • "Access denied" or "permission denied" errors
  • Unable to create databases or tables
  • Read/write operations failing

Solution​

Verify the dab Nexus service account has the required permissions:

  • Application Database: db_owner role (or db_datareader, db_datawriter, db_ddladmin)
  • Extraction/Results databases: dbcreator role at server level (for auto-creation) or db_owner on pre-created databases

See Setup MS SQL-Server for detailed permission requirements.