Distributed Concurrency Control

Data servers that store primary data provide most of the concurrency control needed for the distributed database system. If a transaction fails to update a primary version of a table, the primary Replication Server does not distribute the update to other sites.

When a transaction succeeds in updating primary data, the Replication Server distributes the changes. Unless a failure occurs, the update succeeds at all sites with subscriptions to the data.

• Transactions that Modify Data in Multiple Databases
  A transaction that modifies primary data in more than one data server may require additional concurrency control.
• Failed Replicate Table Updates
  A modification to primary data may fail to update a copy of the data at a subscribing site.