TDS Connection Pooling
FreeTDS 0.52 was the first to include a TDS Connection Pooling server. It lives in the src/pool directory.
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.
 | 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 was specified with the configure --with-prefix flag option).
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
| Name | Possible Values | Default | Meaning |
|---|---|---|---|
| user | Any valid user | none | The username used to connect to the dataserver. |
| password | Any | none | The password of the user at the dataserver. |
| server | Any TDS 4.2 entry in the freetds.conf file | none | The alias from the freetds.conf file representing the dataserver that will be connected to. |
| database | Any valid database | User's default database | The database on the dataserver to use. |
| port | Any TCP port | none | Port on which tdspool will listen. |
| min pool conn | 1 or more | none | Minimum number of open connections to maintain to the dataserver. |
| max pool conn | 1 or more | none | Maximum number of open connections to open against the dataserver. |
| max member age | 0 (no limit) or a number of seconds | 0 | Maximum age of idle members before connection is closed. |
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 [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.