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What is pgpool-II?

pgpool-II is a middleware that works between PostgreSQL servers and a PostgreSQL database client. It provides the following features.

• Connection Pooling

pgpool-II saves connections to the PostgreSQL servers, and reuse them whenever a new connection with the same properties (i.e. username, database, protocol version) comes in. It reduces connection overhead, and improves system's overall throughput.

• Replication

pgpool-II can manage multiple PostgreSQL servers. Using the replication function enables creating a realtime backup on 2 or more physical disks, so that the service can continue without stopping servers in case of a disk failure.

• Load Balance

If a database is replicated, executing a SELECT query on any server will return the same result. pgpool-II takes an advantage of the replication feature to reduce the load on each PostgreSQL server by distributing SELECT queries among multiple servers, improving system's overall throughput. At best, performance improves proportionally to the number of PostgreSQL servers. Load balance works best in a situation where there are a lot of users executing many queries at the same time.

• Limiting Exceeding Connections

There is a limit on the maximum number of concurrent connections with PostgreSQL, and connections are rejected after this many connections. Setting the maximum number of connections, however, increases resource consumption and affect system performance. pgpool-II also has a limit on the maximum number of connections, but extra connections will be queued instead of returning an error immediately.

• Parallel Query

Using the parallel query function, data can be divided among the multiple servers, so that a query can be executed on all the servers concurrently to reduce the overall execution time. Parallel query works the best when searching large-scale data.

pgpool-II talks PostgreSQL's backend and frontend protocol, and relays a connection between them. Therefore, a database application (frontend) thinks that pgpool-II is the actual PostgreSQL server, and the server (backend) sees pgpool-II as one of its clients. Because pgpool-II is transparent to both the server and the client, an existing database application can be used with pgpool-II almost without a change to its sources.

Where can I get pgpool-II?

pgpool-II is licensed under BSD license. You can download it from pgpool-II development page. The latest stable version of pgpool-II is 3.1.

pgpool-II 3.1 officially released(2011/9/8)

Pgpool-II 3.1 is now officially released. This version supports syslog, more than one standby nodes in streaming replication mode, allow to specify user name with pg_md5 command. You can add new DB node or do online recovery without disturbing existing client sessions.

Also documents are enhanced. Simplified Chinese and French verion of documnets are added.

Learn more about pgpool-II 3.1:

• pgpool-II 3.1 release note(English)
• pgpool-II 3.1 release note(Japanese)