TDS Connection Pooling

The FreeTDS connection pool is a server process, it acts just like a SQL Server. You can use any program to attach to it that you could use to attach to a real SQL Server. The pool in turn connects to the SQL Server and database you specify, and attempts to share these connections. See the README in the pool directory for a more detailed description of its inner workings.

To configure the pooling server, first make sure FreeTDS has a working entry for the real SQL Server by connecting to it with SQSH or another program.

Note

The FreeTDS connection pool currently only supports TDS version 4.2. This restriction applies to both the client-to-pool and pool-to-server connections!

After FreeTDS has been installed, you will find an executable named tdspool in the /usr/local/bin directory (or whatever directory you specified if configure was run using the --with-prefix flag).

Next, edit the pool.conf file in the FreeTDS's etc directory. The pool.conf file is formatted like the freetds.conf with a section name in brackets and options for each section in key/value pairs.

Just like the freetds.conf file there are two types of sections, a [global] section whose options affect all pools, and a section with the name of the pool for pool-specific options. The following options are supported and may appear in either section.

Table 5-1. pool.conf settings

NameDefaultMeaningPossible Values
usernoneThe username used to connect to the dataserver.Any valid user
passwordnoneThe password of the user at the dataserver.Any
servernoneThe alias from the freetds.conf file representing the dataserver that will be connected to.Any TDS 4.2entry in the freetds.conf file
databaseUser's default databaseThe database on the dataserver to use.Any valid database
portnonePort on which tdspool will listen.Any TCP port
min pool connnoneMinimum number of open connections to maintain to the dataserver.1 or more
max pool connnoneMaximum number of open connections to open against the dataserver.1 or more
max member age0Maximum age of idle members before connection is closed.0 (no limit) or a number of seconds

Now, let's put this into practice.

Example 5-6. pool.conf

[global]
	min pool conn = 5
	max pool conn = 10
	max member age = 120

[mypool]
	user = webuser
	password = secret
	database = ebiz
	server = fooserv
	max pool conn = 7
	port = 5000
The [global] section defines that we will open 5 connections against the server initially, and will increase up to 10 as demand requires. These connections will be closed after being idle for 2 minutes (120 seconds), but only until there are 5 remaining open.

The [mypool] section defines a pool named mypool that will listen on port 5000. It will login to a SQL Server named fooserv using the user webuser and the ever so clever password of secret. Once logged in, the connections will use the database ebiz instead of webuser's default database. Also, since this SQL Server has a limited number of CALs (Client Access Licenses), we are restricting the maximum number of connections to 7, which overrides the global setting of 10.

Now you can run tdspool with the name of the pool you are serving.

$  tdspool mypool

Before your clients connect to the pool, you must edit your freetds.conf to include the host and port of the pooling server, and point your clients at it!