Page 314 - Asterisk™: The Future of Telephony

• Multiple readhandles and writehandles can be listed, in order of preference, to
perform failover when the primary handle cannot be contacted (limit of 5)
• prefix will remain unchanged
The current syntax in Asterisk 1.4 will continue to work in the backport, but will display
a deprecation warning in the version to follow. Support will eventually be removed.

ODBC Voicemail

Asterisk contains the ability to store voicemail inside the database using the ODBC
connector. This is useful in a clustered environment where you want to abstract the
voicemail data from the local system so that multiple Asterisk boxes have access to the
same data. Of course, you have to take into consideration that you are centralizing a
part of Asterisk, and you need to take actions to protect that data, such as regular
backups, and possibly clustering the database backend using replication. If you are
using PostgreSQL, there are some good projects for doing this: PGcluster (http://pgfoun
dry.org/projects/pgcluster/) and Slony-I (http://gborg.postgresql.org/project/slony1/proj
display.php).
Asterisk stores the voicemail inside a Binary Large Object (BLOB). When retrieving the
data, it pulls the information out of the BLOB and temporarily stores it on the hard
drive while it is being played back to the user. Asterisk then removes the BLOB and
records from the database when the user deletes the voicemail. Many databases, such
as MySQL, contain native support for BLOBs, but PostgreSQL has a couple of extra
steps required to utilize this functionality that we’ll explore in this section. When you’re
done, you’ll be able to record, play back, and delete voicemail data from the database
just as if it were stored on the local hard drive.

This section builds upon previous configuration sections in this chapter.
If you have not already done so, be sure to follow the steps in the
“Installing the Database” and “Installing and Configuring ODBC” sec-
tions before continuing. In the “Installing and Configuring ODBC”
section, be sure you have enabled ODBC_STORAGE in the menuselect system
under Voicemail Options.

Creating the Large Object Type
We have to tell PostgreSQL how to handle the large objects. This includes creating a
trigger to clean up the data when we delete a record from the database that references
a large object.

Connect to the database as the asterisk user from the console:
# psql -h localhost -U asterisk asterisk
Password:

286 | Chapter 12: Relational Database Integration