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Continuous Availability with Shadowbase and Active/Active Systems

Active/Active - What is an Active/Active System?

An active/active system is a network of independent processing nodes, each having access to a common replicated database, so that all nodes participate in a common application. In a general case, the nodes are completely symmetric; any transaction can be routed within the application network to any node which reads or updates any set of data items in the database. This approach provides the most flexibility and maximizes system investment as requests are load-balanced across all available processing capacity. If a node fails, users at the other nodes are unaffected. Furthermore, the users at the failed node are quickly switched to surviving nodes, thus restoring their services in seconds or less.

An active/active network contains at least two copies of the application database. All database copies are kept in synchronization so that any copy can be used for a transaction. If a database copy fails, all transactions are routed to a surviving copy. Providing that the nodes and database copies are geographically distributed, active/active systems provide disaster recovery for little or no cost. If a disaster knocks out a node or a database copy, there are others in the network to take their place.

Active/Active Architecture

Active/Active Architecture

Active/Active - Why Does Active/Active Work?

The availability of a system is determined by the amount of time that it is operational (the system uptime) as compared to the amount of time that service is being denied to one or more users (the system downtime). Although certain techniques are used to improve the uptime of an individual system, (such as increasing operator training and using fault-tolerant components), there is a point when not much more can be done to add the necessary orders of magnitude to the uptime into the extreme reliability realm. Improving the uptime is ultimately determined by hardware and software reliability, operator accuracy, etc. Active/active technology reduces downtime by orders of magnitude.

If a node fails, users at that node are switched to another operable node. If a database fails, there is another consistent copy in the network that is used. If a network component fails, alternate routes are provided. Using technology available today, failure recovery is achieved in seconds or less. In short, let it fail, but fix it fast.

Active/Active - Shadowbase® Data Synchronization

Synchronization of the databases is a key requirement for implementing an active/active system. Each database copy must always stay in a consistent state and must reflect the current state of the application. Shadowbase software accomplishes this task by replicating changes made to each database copy to all other copies in the application network. Shadowbase technology contains a powerful database replication engine which provides bi-directional replication between the database copies and guarantees that all copies remain in a consistent and correct state. Coupled with the Shadowbase AutoLoader™, a powerful online loading utility, the Shadowbase tool set provides everything necessary to convert an existing application into an active/active architecture.

Data collisions are a concern that must be addressed in active/active database synchronization. A data collision occurs when two nodes make a change to the same row in the database at substantially the same time. Each copy will replicate its change to the other database copy, thus overwriting the change made there. As a result, the database copies are different and both are wrong. Shadowbase software detects collisions and automatically resolves them in many cases.

Active/Active - Eliminate Planned Downtime

With Shadowbase active/active systems, you do not need to take the production application down and deny service to your users to upgrade hardware, software, the database, or the application itself. You do need to switch users from the node about to be upgraded to another node, perform the upgrade, test it, and then return the users to the upgraded node. This way upgrades are rolled through all nodes in the application network without ever denying service to a user. In addition, the system’s capacity can be easily expanded by adding new nodes in a similar method.

Shadowbase technology provides the tools necessary for these zero downtime migrations. Its online copy facility, the Shadowbase AutoLoader, recreates the current state of the database on the new or upgraded node. Its data replication engine then keeps this database copy current until users are returned to that node. Shadowbase technology provides the facilities to move the users to other nodes without losing their data if a problem occurs with the new node.

Active/Active - Why Choose Shadowbase Technology?

Shadowbase technology is the recognized leader in data replication for active/active systems. Its avoidance of disk queuing points makes it the fastest and most efficient active/active data replication engine on the market. Fast replication means fewer data collisions and less potential data loss following a node failure. Furthermore, its efficient replication path means less utilization of computing resources for replication. Shadowbase software is easy to manage and is itself fault-tolerant. Of utmost importance is Shadowbase software’s attention to referential integrity. It guarantees that every database copy is always consistent and correct. Aiding this integrity is Shadowbase technology’s superior capabilities to automatically detect and resolve data collisions.

Furthermore, Shadowbase technology’s online copy utility, the Shadowbase AutoLoader, copies an active database while it actively updates. Any portion of the database that is copied is immediately consistent and correct and can be used for application processing. Shadowbase technology is also fully heterogeneous and is used on popular systems such as UNIX, Linux and Windows running Oracle and SQL Server databases, and NonStop servers using NonStop SQL and Enscribe databases. Contact us for the availability of additional offerings, such as Sybase, MySQL, and DB2. Click here to view all of the Shadowbase Supported Platforms and Databases.

For more information, please read our white papers: Choosing a Business Continuity Solution to Match Your Business Availability Requirements and Achieving Century Uptimes with Shadowbase® Active/Active Technology or see our webcast: Advances in Active/Active - Asynchronous and Synchronous Replication State-of-the-Art.