PEM server and agent connection management mechanism
====================================================

You can manage the connections effectively either through a moderate
number or with connection pooling in Postgres Enterprise Manager (PEM).

You can use PgBouncer as a connection pooler for limiting the number of
connections from the PEM agent to the PEM server on non-Windows
machines.

You can see below how PEM agents manage database connections both with
and without the use of PgBouncer as a connection pooler.

Without PgBouncer
-----------------

In the default configuration, each PEM agent connects to the PEM
database server directly using SSL for encryption. Each PEM agent uses
its own dedicated user for the connection.

For example, a user agent with ID 1 connects to the PEM database server
as agent1.

.. figure:: /images/pem_without_pgbouncer.png
   :width: 70% 
   :alt: Connecting to the PEM database without PgBouncer

   Connecting to the PEM database without PgBouncer

With PgBouncer
--------------

In a PgBouncer-enabled environment, PEM agents can’t connect to the PEM
database server directly. PEM agents must use a proxy user that you
configure specifically for the connection to PgBouncer. In the example,
the proxy user handling all PEM agent connections is called
``pem_agent_user1`` .

Once the PEM agents connect to PgBouncer using SSL, PgBouncer is
responsible for managing connection requests to the PEM database server.
PgBouncer uses the rules you configured for connection pooling to manage
the incoming connection requests, for example, by respecting the
established maximum number of active connections.

.. figure:: /images/pem_with_pgbouncer.png
   :width: 70% 
   :alt: Connecting to pgBouncer.

   Connecting to pgBouncer.

!!!note Use PgBouncer version 1.9.0 or later as the connection pooler.
Versions 1.9.0 or later support cert authentication.

For more information about configuring PgBouncer with PEM, see
:ref:`Connection pooling using PgBouncer <Connection pooling using PgBouncer>`  .