Sybase 12.4.2 Introduction to versioning, Concurrency and IQ Multiplex, Concurrency for backups

CHAPTER 8 Transactions and Versioning

Concurrency and IQ Multiplex

IQ Multiplex extends Adaptive Server IQ to allow concurrent processing of read transactions on multiple Adaptive Server IQ servers. IQ Multiplex extends snapshot versioning to maintain the consistency of the database across multiple servers. For more information about using IQ Multiplex, see Adaptive Server IQ Multiplex User’s Guide .

Concurrency for backups

Adaptive Server IQ also uses transaction processing and snapshot versioning to allow you to back up your database concurrently with read and write operations. Restore operations, however, require exclusive access, because they write to the database. See Chapter 11, “Backup and Data Recovery” for more information on concurrency issues for backup and restore operations.

Why concurrency benefits you

A data warehouse is a common repository of information shared by a large number of people. These people may need frequent access to the information. To avoid impeding their work, the database server must be able to process many transactions at the same time.

Moreover, many sites also require frequent updates to the database. In high availability sites, the DBA cannot postpone insertions and deletions to a time when exclusive access is possible. Similarly, it is important to be able to back up the database on a regular basis, without disrupting the activities of other users.

Adaptive Server IQ's approach to concurrency gives query users immediate access to information, and allows you to ensure the safety and accuracy of the information they receive.

Introduction to versioning

Adaptive Server IQ uses snapshot versioning to allow transactions to operate concurrently.

You can think of snapshot versioning as you would a snapshot you take with a camera. When you photograph a snapshot of an object or scene, you get an image of it as it appears at a given moment in time. Likewise, when IQ takes a snapshot of an object in your database, it retains an image of that object at a given instant in time.

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