TDS Connection Pooling
The Connection Pooling server swims in the src/pool directory.
The FreeTDS connection pool is a server process; it emulates a SQL Server. Any program that can attach to a real SQL Server may instead elect to attach to the pool server. The pool in turn connects to the SQL Server and database you specify, and attempts to share these connections. See the src/pool/README for a more detailed description of its inner workings.
To configure the pool 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).
Edit pool.conf in the FreeTDS's etc directory. The pool.conf file is formatted like freetds.conf, with a section name in brackets and options for each section in key/value pairs.
Just as in freetds.conf 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 servername. |
| password | Any | none | The password of the user at the servername. |
| server | Any TDS 4.2 entry in the freetds.conf file | none | The alias from the freetds.conf file representing the servername that will be connected to. |
| database | Any valid database | User's default database | The database on the servername 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 servername. |
| max pool conn | 1 or more | none | Maximum number of open connections to open against the servername. |
| 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 5-8. 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.
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.