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LISTEN(5)
NAME
  LISTEN - listen for a notification

SYNOPSIS
  LISTEN name

  INPUTS

  name Name of notify condition.

  OUTPUTS

  LISTEN
       Message returned upon successful completion of registration.

  WARNING: Async_Listen: We are already listening on name
       If this backend is already registered for that notify condition.

DESCRIPTION
  LISTEN registers the current PostgreSQL backend as a listener on the notify
  condition name.

  Whenever the command NOTIFY name is invoked, either by this backend or
  another one connected to the same database, all the backends currently
  listening on that notify condition are notified, and each will in turn
  notify its connected frontend application. See the discussion of NOTIFY for
  more information.

  A backend can be unregistered for a given notify condition with the
  UNLISTEN command. Also, a backend's listen registrations are automatically
  cleared when the backend process exits.

  The method a frontend application must use to detect notify 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 routine PQnotifies to find out whether
  any notify 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 library you are using for
  more details.

  NOTIFY [notify(5)] contains a more extensive discussion of the use of
  LISTEN and NOTIFY.

  NOTES

  name can be any string valid as a name; it need not correspond to the name
  of any actual table. If notifyname is enclosed in double-quotes, it need
  not even be a syntactically valid name, but can be any string up to 63
  characters long.

  In some previous releases of PostgreSQL, name had to be enclosed in
  double-quotes when it did not correspond to any existing table name, even
  if syntactically valid as a name. That is no longer required.

USAGE
  Configure and execute a listen/notify sequence from psql:

  LISTEN virtual;
  NOTIFY virtual;

  Asynchronous NOTIFY 'virtual' from backend with pid '8448' received.

COMPATIBILITY
  SQL92

  There is no LISTEN in SQL92.

Index for Section 5

Alphabetical listing for L

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