Built-in replication needed to be added to the Postgres Plus to make it competitive with commercial systems, which already contain the feature, acknowledged Robin Schumacher, EnterpriseDB director of product strategy. The PostgreSQL open source project serves as the code base for Postgres Plus. Project managers added the feature in the 9.0 version, which was released on Sept. 20, and EnterpriseDB said its Postgres Plus product supported the new code base immediately.
With built-in replication, a second database server can serve as a satellite or secondary system to a master system. The replicated data set is created by forwarding the activity captured in the write-ahead log to the secondary system. The replication will trail slightly the master copy. The streaming replication method is asynchronous but the two database servers will maintain identical data sets and one can be recovered from the other, Schmacher said in an interview.
The built-in replication gives Postgres Plus a greater ability to scale out to more servers and fail-over more easily in case of database failure, giving Postgres Plus a better high availability profile.
The 9.0 version also allows the master database to query a standby system, giving both the open source system and Postgres Plus hot-standby capability. "Built in replication and hot standby have been the most requested features for many years," said Simon Riggs, lead contributor to hot standby in the PostgreSQL open source project and CTO of of 2ndQuadrant, a firm that supplies technical support for PostgreSQL systems. Riggs made the comment in the announcement of the 9.0 version by the open source project.
Catching up with built-in replication might sound like just another trailing edge feature of open source databases, sometimes cited for their slow adoption rate inside the enterprise. But any additional features that match the commercial systems are heeded in the case of Postgres Plus because it contains an Oracle compatibility layer, allowing most applications that run under Oracle to also run under Postgres Plus, Schumacher said. Postgres Plus recognizes Oracle's PL/SQL variant of the SQL data access language. Stored procedures and triggers in Oracle can be transferred to and run in Postgres Plus, he said.
Among other things, the EnterpriseDB system also works on servers running the 64-bit Windows Server operating system, which along with Linux, is one of the fastest growing operating systems in the data center. Postgres Plus also supports the ability of the 9.0 version of the open source code to continue running while an upgrade or patch to the system takes place. In the past, an upgrade required the data to be transferred to an auxiliary system, then back after the upgrade had taken place, Schumacher said.
The 9.0 version of the open source code base was generated by about 100 core contributors and another 150 occasional contributors. PostgreSQL meets the ACID (atomicity, consistency, isolation, and durability) standard for relational systems, guaranteeing transaction integrity.