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03 May 2011, 14:59

PostgreSQL 9.1 beta adds synchronous replication

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PostgreSQL Logo PostgreSQL 9.1 should be out within the next four months; the development team has now released the first beta version of the open source SQL database. It includes a synchronous replication mode which ensures that transactions concluded with COMMIT will always reach slave nodes. Asynchronous replication, until now the only available replication mode, has the drawback that data loss can occur if the master crashes after the COMMIT but before sending the data to the slaves. Synchronous replication ensures that, for each write transaction, the master waits until at least one slave node has written the data to its transaction log. This increase in reliability comes at the cost of longer response times. PostgreSQL 9.1 will continue to offer asynchronous replication.

Data security will also be enhanced in 9.1 by the 'serializable' isolation level. This ensures that performing multiple transactions simultaneously has the same effect as performing them sequentially. Although this isolation level was available in previous versions of PostgreSQL, the implementation actually produced what the standard specifies as a 'repeatable read' level. The new serialisable implementation uses no locks, ensuring that operations cannot block one another. If transactions cannot be serialised, the server performs only one of them, aborts, and issues an error message.

PostgreSQL 9.1 also improves its internationalisation capabilities by allowing COLLATE rules for individual columns, indices and expressions. Previously, collation could only be set for the entire database at database creation. New rules can be created using CREATE COLLATION.

A list of changes can be found in the release notes. To enable them to keep to their planned release schedule, the development team is asking users to subject the beta to exhaustive testing. The source code, as well as executable versions for Free BSD, Mac OS X, Linux, Solaris and Windows, are available from the PostgreSQL download page.

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