| PostgreSQL 7.4.30 Documentation | ||||
|---|---|---|---|---|
| Prev | Fast Backward | Fast Forward | Next | |
pg_listen creates, changes, or
cancels a request to listen for asynchronous notification
messages from the PostgreSQL
server. With a callbackCommand
parameter, the request is established, or the command string of
an already existing request is replaced. With no callbackCommand parameter, a prior request is
canceled.
After a pg_listen request is
established, the specified command string is executed whenever a
notification message bearing the given name arrives from the
server. This occurs when any PostgreSQL client application issues a
NOTIFY command referencing that name. The command string
is executed from the Tcl idle loop. That is the normal idle state
of an application written with Tk. In non-Tk Tcl shells, you can
execute update or vwait to cause the idle loop to be entered.
You should not invoke the SQL statements LISTEN or UNLISTEN
directly when using pg_listen.
pgtcl takes care of issuing
those statements for you. But if you want to send a notification
message yourself, invoke the SQL NOTIFY
statement using pg_exec.