PgBouncer FAQ

How to connect to PgBouncer?

PgBouncer acts as Postgres server, so simply point your client to PgBouncer port.

How to load-balance queries between several servers?

PgBouncer does not have internal multi-host configuration. It is possible via some external tools:

  1. DNS round-robin. Use several IPs behind one DNS name. PgBouncer does not look up DNS each time new connection is launched. Instead it caches all IPs and does round-robin internally. Note: if there is more than 8 IPs behind one name, the DNS backend must support EDNS0 protocol. See README for details.

  2. Use a TCP connection load-balancer. Either LVS or HAProxy seem to be good choices. On PgBouncer side it may be good idea to make server_lifetime smaller and also turn server_round_robin on - by default idle connections are reused by LIFO algorithm which may work not so well when load-balancing is needed.

How to failover

PgBouncer does not have internal failover-host configuration nor detection. It is possible via some external tools:

  1. DNS reconfiguration - when ip behind DNS name is reconfigured, pgbouncer will reconnect to new server. This behaviour can be tuned via 2 config parameters - dns_max_ttl tunes lifetime for one hostname, and dns_zone_check_period tunes how often zone SOA will be queried for changes. If zone SOA record has changed, pgbouncer will re-query all hostnames under that zone.

  2. Write new host to config and let PgBouncer reload it - send SIGHUP or use RELOAD; command on console. PgBouncer will detect changed host config and reconnect to new server.

How to use SSL connections with PgBouncer?

Since version 1.7, PgBouncer has built-in support for TLS. Just configure it.

[ Old answer for older PgBouncer versions. ]

Use Stunnel. Since version 4.27 it supports PostgreSQL protocol for both client and server side. It is activated by setting protocol=pgsql.

Alternative is to use Stunnel on both sides of connection, then the protocol support is not needed.

How to use prepared statements with session pooling?

In session pooling mode, the reset query must clean old prepared statements. This can be achieved by server_reset_query = DISCARD ALL; or at least to DEALLOCATE ALL;

How to use prepared statements with transaction pooling?

To make prepared statements work in this mode would need PgBouncer to keep track of them internally, which it does not do. So only way to keep using PgBouncer in this mode is to disable prepared statements in the client.

Disabling prepared statements in JDBC

The proper way to do it for JDBC is adding prepareThreshold=0 parameter to connect string.

Disabling prepared statements in PHP/PDO

To disable use of server-side prepared statements, the PDO attribute PDO::ATTR_EMULATE_PREPARES must be set to true. Either at connect-time:

$db = new PDO("dsn", "user", "pass", array(PDO::ATTR_EMULATE_PREPARES => true));

or later:

$db->setAttribute(PDO::ATTR_EMULATE_PREPARES, true);

How to upgrade PgBouncer without dropping connections?

[ This cannot be done with TLS connections. ]

This is as easy as launching new PgBouncer process with -R switch and same config:

$ pgbouncer -R -d config.ini

The -R (reboot) switch makes new process connect to console of the old process (dbname=pgbouncer) via unix socket and issue following commands:

SUSPEND;
SHOW FDS;
SHUTDOWN;

After that if new one notices old one gone it resumes work with old connections. The magic happens during SHOW FDS command which transports actual file descriptors to new process.

If the takeover does not work for whatever reason, the new process can be simply killed, old one notices this and resumes work.

How to know which client is on which server connection?

Use SHOW CLIENTS and SHOW SERVERS views on console.

  1. Use ptr and link to map local client connection to server connection.

  2. Use addr and port of client connection to identify TCP connection from client.

  3. Use local_addr and local_port to identify TCP connection to server.

Overview of important fields in SHOW CLIENTS

addr, port
source address of client connection
local_addr, local_port
local endpoint of client connection
ptr
unique id for this connection
link
unique id for server connection this client connection is currently linked to

Overview of important fields in SHOW SERVERS

addr, port
server address pgbouncer connects to
local_addr, local_port
connections local endpoint
ptr
unique id for this connection
link
unique id for client connection this server connection is currently linked to

Should PgBouncer be installed on webserver or database server?

It depends. Installing on webserver is good when short-connections are used, then the connection setup latency is minimised - TCP requires couple of packet roundtrips before connection is usable. Installing on database server is good when there are many different hosts (eg. webservers) connecting to it, then their connections can be optimised together.

It is also possible to install PgBouncer on both webserver and database servers. Only negative aspect of that is that each PgBouncer hop adds small amount of latency to each query. So it’s probably best to simply test whether the payoff is worth the cost.