From PostgreSQL wiki
PgBouncer is a lightweight connection pooler for PostgreSQL.
Stable, in production.
- Several levels of brutality when rotating connections:
- Session pooling
- Most polite method. When client connects, a server connection will be assigned to it for the whole duration it stays connected. When client disconnects, the server connection will be put back into pool. This mode supports all PostgeSQL features.
- Transaction pooling
- Server connection is assigned to client only during a transaction. When PgBouncer notices that transaction is over, the server will be put back into pool.
- This mode breaks few session-based features of PostgreSQL. You can use it only when application cooperates by not using features that break. See the table below for incompatible features.
- Statement pooling
- Most aggressive method. This is transaction pooling with a twist - multi-statement transactions are disallowed. This is meant to enforce "autocommit" mode on client, mostly targeted for PL/Proxy.
- Low memory requirements (2k per connection by default). This is due to the fact that PgBouncer does not need to see full packet at once.
- It is not tied to one backend server, the destination databases can reside on different hosts.
- Supports online reconfiguration for most of the settings.
- Supports online restart/upgrade without dropping client connections.
- Supports protocol V3 only, so backend version must be >= 7.4.
- Command line usage.
- Config file documentation.
- FAQ: Load-balancing, SSL, prepared statements, online restart.
- Official releases, bugtracker: http://pgfoundry.org/projects/pgbouncer
- GIT: git://git.postgresql.org/git/pgbouncer.git (GitWeb) (github)
- RPM: http://yum.postgresql.org/
Various OS distributions have their native package/port of PgBouncer. So it might be good to first check if it is already available on your OS.
- Mailing List: http://lists.pgfoundry.org/mailman/listinfo/pgbouncer-general
- Bugtracker: http://pgfoundry.org/projects/pgbouncer/
Feature matrix for pooling modes
Following table list various PostgreSQL features and whether they are compatible with PgBouncer pooling modes. Note that 'transaction' pooling breaks client expectations of server by design and can be used only if application cooperates by not using non-working features.
|Feature||Session pooling ||Transaction pooling|
|Startup parameters ||Yes||Yes|
|WITHOUT HOLD CURSOR||Yes||Yes|
|WITH HOLD CURSOR||Yes||No|
|Protocol-level prepared plans||Yes||No |
|PREPARE / DEALLOCATE||Yes||No|
|ON COMMIT DROP temp tables||Yes||Yes|
|PRESERVE/DELETE ROWS temp tables||Yes||No|
|Cached plan reset||Yes||Yes |
|UDFs with session state||Yes||No|
-  - Full transparency requires PostgreSQL 8.3 and PgBouncer 1.1+ with server_reset_query = DISCARD ALL
-  - Startup parameters are: client_encoding, datestyle, timezone, standard_conforming_strings and application_name. PgBouncer can detect their changes so it can guarantee they remain consistent for client. Available from PgBouncer 1.1.
-  - It is possible to add support for that into PgBouncer.