DDL Gateway Server - Teradata Meta Data Services

DDL Gateway Server

The MDS DDL Gateway Server will keep track of the database names of all DDL transactions that it has received messages for. It will track the transaction in a backlog list and in a log file. The log will be combined with the MDS Recovery Table to resync the repository. Only databases that are out-of-sync will be resynced during recovery.

The DDL Gateway Server performs recovery:

On startup of the DDL Gateway. On startup, the Gateway Server looks in the MDS Recovery Table and in its own log to determine which databases need recovery. If the Teradata Database System is configured in MDS to have the “Recovery On Startup” flag enabled, the Gateway will begin recovery for that system. If the flag is not set, recovery will be deferred until the scheduled time.

When the DDL Gateway receives a “Recover now” message from the MDS Action Processor. Scheduled recovery will only occur once per day for each Teradata Database System based on the schedule configured for that system in MDS. The schedule configuration also specifies the days of the week to perform scheduled recovery.

The Gateway Server performs the following steps when performing recovery:

1 The Gateway Server sends a message to the Teradata Database to stop sending DDLs to RSG and to log “Affected” databases in the MDS Recovery Table.

2 The Gateway Server reads and deletes MDS Recovery Table entries, reads the backlog list and compiles a list of database names to resync.

3 Calls the metaload utility to resync each database name.

4 Reads and deletes the MDS Recovery Table again to resync databases that may have been affected by DDLs during the resync process.

5 Sends a message to the Teradata Database to start sending DDLs to RSG.