| PostgreSQL 7.4.3 Documentation | ||||
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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.