162 lines
3.5 KiB
Plaintext
162 lines
3.5 KiB
Plaintext
<REFENTRY ID="SQL-NOTIFY">
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<REFMETA>
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<REFENTRYTITLE>
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NOTIFY
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</REFENTRYTITLE>
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<REFMISCINFO>SQL - Language Statements</REFMISCINFO>
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</REFMETA>
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<REFNAMEDIV>
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<REFNAME>
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NOTIFY
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</REFNAME>
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<REFPURPOSE>
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Signals all frontends and backends listening on a class
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</REFPURPOSE>
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<REFSYNOPSISDIV>
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<REFSYNOPSISDIVINFO>
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<DATE>1998-09-01</DATE>
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</REFSYNOPSISDIVINFO>
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<SYNOPSIS>
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<REPLACEABLE CLASS="PARAMETER">
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</REPLACEABLE>
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NOTIFY <REPLACEABLE CLASS="PARAMETER">classname</REPLACEABLE>
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</SYNOPSIS>
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<REFSECT2 ID="R2-SQL-NOTIFY-1">
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<REFSECT2INFO>
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<DATE>1998-09-01</DATE>
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</REFSECT2INFO>
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<TITLE>
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Inputs
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</TITLE>
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<PARA>
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</PARA>
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<VARIABLELIST>
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<VARLISTENTRY>
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<TERM>
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<REPLACEABLE CLASS="PARAMETER">classname</REPLACEABLE>
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</TERM>
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<LISTITEM>
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<PARA>
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Table or arbitrary relation class used for notification.
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</VARIABLELIST>
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</REFSECT2>
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<REFSECT2 ID="R2-SQL-NOTIFY-2">
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<REFSECT2INFO>
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<DATE>1998-09-01</DATE>
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</REFSECT2INFO>
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<TITLE>
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Outputs
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</TITLE>
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<PARA>
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</PARA>
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<VARIABLELIST>
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<VARLISTENTRY>
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<TERM>
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NOTIFY
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</TERM>
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<LISTITEM>
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<PARA>
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Notification message from backend.
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</VARIABLELIST>
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</REFSECT2>
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</REFSYNOPSISDIV>
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<REFSECT1 ID="R1-SQL-NOTIFY-1">
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<REFSECT1INFO>
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<DATE>1998-09-01</DATE>
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</REFSECT1INFO>
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<TITLE>
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Description
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</TITLE>
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<PARA>
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NOTIFY is used to awaken all backends and consequently all
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frontends that have executed <command>LISTEN</command> on
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<replaceable class="parameter">classname</replaceable>.
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This can be used either within an instance-level rule
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as part of the action body or from a normal query.
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<para>
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When used from within a normal query,
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this can be thought of as interprocess communication (IPC). When
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used from within a rule, this can be thought of as an alerter mechanism.
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<para>
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Notice that the mere fact that a notify has been
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executed does not imply anything in particular about the state
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of the class (e.g., that it has been updated),
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nor does the notification protocol transmit any useful information
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other than the class name.
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Therefore, all notify does is indicate that some backend wishes its peers to
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examine <replaceable class="parameter">classname</replaceable>
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in some application-specific way.
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<para>
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In fact, <replaceable class="parameter">classname</replaceable>
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need not be the name of an SQL class at all.
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It is best thought of as a condition name
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that the application programmer selects.
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<para>
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This event notification is performed through the libpq protocol
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and frontend application interface. The application program
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must call the routine <function>PQnotifies</function> in order to find out the
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name of the class to which a given
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notification corresponds.
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If this code is not included in the application,
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the event notification will be
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queued and never be processed.
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<REFSECT2 ID="R2-SQL-NOTIFY-3">
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<REFSECT2INFO>
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<DATE>1998-09-01</DATE>
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</REFSECT2INFO>
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<TITLE>
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Notes
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</TITLE>
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<PARA>
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</PARA>
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</REFSECT2>
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<REFSECT1 ID="R1-SQL-NOTIFY-2">
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<TITLE>
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Usage
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</TITLE>
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<PARA>
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</PARA>
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<ProgramListing>
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-- Configure and execute a listen/notify sequence
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-- from psql
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postgres=> create table t (i int4);
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postgres=> listen t;
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LISTEN
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postgres=> notify t;
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NOTIFY
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ASYNC NOTIFY of 't' from backend pid '10949' received
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</ProgramListing>
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</REFSECT1>
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<REFSECT1 ID="R1-SQL-NOTIFY-3">
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<TITLE>
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Compatibility
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</TITLE>
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<PARA>
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</PARA>
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<REFSECT2 ID="R2-SQL-NOTIFY-4">
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<REFSECT2INFO>
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<DATE>1998-09-01</DATE>
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</REFSECT2INFO>
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<TITLE>
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SQL92
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</TITLE>
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<PARA>
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There is no NOTIFY statement in <acronym>SQL92</acronym>.
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</REFENTRY>
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