LISTEN(7)

NAME

   LISTEN - listen for a notification

SYNOPSIS

   LISTEN channel

DESCRIPTION

   LISTEN registers the current session as a listener on the notification
   channel named channel. If the current session is already registered as
   a listener for this notification channel, nothing is done.

   Whenever the command NOTIFY channel is invoked, either by this session
   or another one connected to the same database, all the sessions
   currently listening on that notification channel are notified, and each
   will in turn notify its connected client application.

   A session can be unregistered for a given notification channel with the
   UNLISTEN command. A session's listen registrations are automatically
   cleared when the session ends.

   The method a client application must use to detect notification events
   depends on which PostgreSQL application programming interface it uses.
   With the libpq library, the application issues LISTEN as an ordinary
   SQL command, and then must periodically call the function PQnotifies to
   find out whether any notification events have been received. Other
   interfaces such as libpgtcl provide higher-level methods for handling
   notify events; indeed, with libpgtcl the application programmer should
   not even issue LISTEN or UNLISTEN directly. See the documentation for
   the interface you are using for more details.

   NOTIFY(7) contains a more extensive discussion of the use of LISTEN and
   NOTIFY.

PARAMETERS

   channel
       Name of a notification channel (any identifier).

NOTES

   LISTEN takes effect at transaction commit. If LISTEN or UNLISTEN is
   executed within a transaction that later rolls back, the set of
   notification channels being listened to is unchanged.

   A transaction that has executed LISTEN cannot be prepared for two-phase
   commit.

EXAMPLES

   Configure and execute a listen/notify sequence from psql:

       LISTEN virtual;
       NOTIFY virtual;
       Asynchronous notification "virtual" received from server process with PID 8448.

COMPATIBILITY

   There is no LISTEN statement in the SQL standard.

SEE ALSO

   NOTIFY(7), UNLISTEN(7)

Opportunity

Personal Opportunity - Free software gives you access to billions of dollars of software at no cost. Use this software for your business, personal use or to develop a profitable skill. Access to source code provides access to a level of capabilities/information that companies protect though copyrights. Open source is a core component of the Internet and it is available to you. Leverage the billions of dollars in resources and capabilities to build a career, establish a business or change the world. The potential is endless for those who understand the opportunity.

Business Opportunity - Goldman Sachs, IBM and countless large corporations are leveraging open source to reduce costs, develop products and increase their bottom lines. Learn what these companies know about open source and how open source can give you the advantage.

Free Software

Free Software provides computer programs and capabilities at no cost but more importantly, it provides the freedom to run, edit, contribute to, and share the software. The importance of free software is a matter of access, not price. Software at no cost is a benefit but ownership rights to the software and source code is far more significant.

Free Office Software - The Libre Office suite provides top desktop productivity tools for free. This includes, a word processor, spreadsheet, presentation engine, drawing and flowcharting, database and math applications. Libre Office is available for Linux or Windows.

Free Books

The Free Books Library is a collection of thousands of the most popular public domain books in an online readable format. The collection includes great classical literature and more recent works where the U.S. copyright has expired. These books are yours to read and use without restrictions.

Source Code - Want to change a program or know how it works? Open Source provides the source code for its programs so that anyone can use, modify or learn how to write those programs themselves. Visit the GNU source code repositories to download the source.

Education

Study at Harvard, Stanford or MIT - Open edX provides free online courses from Harvard, MIT, Columbia, UC Berkeley and other top Universities. Hundreds of courses for almost all major subjects and course levels. Open edx also offers some paid courses and selected certifications.

Linux Manual Pages - A man or manual page is a form of software documentation found on Linux/Unix operating systems. Topics covered include computer programs (including library and system calls), formal standards and conventions, and even abstract concepts.