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Triggered change notifications.
Kevin Grittner, reviewed (in earlier versions) by Álvaro Herrera
1 parent c8397bd commit 6e3323d

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‎contrib/Makefile

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@@ -45,6 +45,7 @@ SUBDIRS = \
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seg \
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spi \
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tablefunc \
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tcn \
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test_parser \
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tsearch2 \
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unaccent \

‎contrib/tcn/Makefile

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# contrib/tcn/Makefile
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MODULES = tcn
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EXTENSION = tcn
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DATA = tcn--1.0.sql
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ifdef USE_PGXS
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PG_CONFIG = pg_config
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PGXS := $(shell $(PG_CONFIG) --pgxs)
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include $(PGXS)
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else
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subdir = contrib/tcn
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top_builddir = ../..
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include $(top_builddir)/src/Makefile.global
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include $(top_srcdir)/contrib/contrib-global.mk
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endif

‎contrib/tcn/tcn--1.0.sql

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/* contrib/tcn/tcn--1.0.sql */
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-- complain if script is sourced in psql, rather than via CREATE EXTENSION
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\echo Use "CREATE EXTENSION tcn" to load this file. \quit
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CREATE FUNCTION triggered_change_notification()
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RETURNS pg_catalog.trigger
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AS 'MODULE_PATHNAME'
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LANGUAGE C;

‎contrib/tcn/tcn.c

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/*-------------------------------------------------------------------------
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*
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* tcn.c
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* triggered change notification support for PostgreSQL
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*
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* Portions Copyright (c) 2011-2012, PostgreSQL Global Development Group
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* Portions Copyright (c) 1994, Regents of the University of California
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*
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*
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* IDENTIFICATION
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* contrib/tcn/tcn.c
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*
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*-------------------------------------------------------------------------
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*/
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#include "postgres.h"
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#include "executor/spi.h"
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#include "commands/async.h"
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#include "commands/trigger.h"
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#include "lib/stringinfo.h"
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#include "utils/rel.h"
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#include "utils/syscache.h"
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PG_MODULE_MAGIC;
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/* forward declarations */
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Datum triggered_change_notification(PG_FUNCTION_ARGS);
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/*
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* Copy from s (for source) to r (for result), wrapping with q (quote)
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* characters and doubling any quote characters found.
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*/
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static void
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strcpy_quoted(StringInfo r, const char *s, const char q)
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{
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appendStringInfoCharMacro(r, q);
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while (*s)
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{
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if (*s == q)
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appendStringInfoCharMacro(r, q);
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appendStringInfoCharMacro(r, *s);
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s++;
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}
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appendStringInfoCharMacro(r, q);
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}
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/*
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* triggered_change_notification
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*
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* This trigger function will send a notification of data modification with
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* primary key values. The channel will be "tcn" unless the trigger is
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* created with a parameter, in which case that parameter will be used.
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*/
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PG_FUNCTION_INFO_V1(triggered_change_notification);
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Datum
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triggered_change_notification(PG_FUNCTION_ARGS)
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{
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TriggerData *trigdata = (TriggerData *) fcinfo->context;
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Trigger *trigger;
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int nargs;
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HeapTuple trigtuple;
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Relation rel;
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TupleDesc tupdesc;
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char *channel;
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char operation;
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StringInfo payload = makeStringInfo();
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bool foundPK;
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List *indexoidlist;
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ListCell *indexoidscan;
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/* make sure it's called as a trigger */
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if (!CALLED_AS_TRIGGER(fcinfo))
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ereport(ERROR,
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(errcode(ERRCODE_E_R_I_E_TRIGGER_PROTOCOL_VIOLATED),
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errmsg("triggered_change_notification: must be called as trigger")));
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/* and that it's called after the change */
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if (!TRIGGER_FIRED_AFTER(trigdata->tg_event))
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ereport(ERROR,
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(errcode(ERRCODE_E_R_I_E_TRIGGER_PROTOCOL_VIOLATED),
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errmsg("triggered_change_notification: must be called after the change")));
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/* and that it's called for each row */
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if (!TRIGGER_FIRED_FOR_ROW(trigdata->tg_event))
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ereport(ERROR,
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(errcode(ERRCODE_E_R_I_E_TRIGGER_PROTOCOL_VIOLATED),
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errmsg("triggered_change_notification: must be called for each row")));
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if (TRIGGER_FIRED_BY_INSERT(trigdata->tg_event))
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operation = 'I';
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else if (TRIGGER_FIRED_BY_UPDATE(trigdata->tg_event))
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operation = 'U';
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else if (TRIGGER_FIRED_BY_DELETE(trigdata->tg_event))
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operation = 'D';
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else
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{
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elog(ERROR, "triggered_change_notification: trigger fired by unrecognized operation");
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operation = 'X'; /* silence compiler warning */
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}
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trigger = trigdata->tg_trigger;
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nargs = trigger->tgnargs;
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if (nargs > 1)
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ereport(ERROR,
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(errcode(ERRCODE_E_R_I_E_TRIGGER_PROTOCOL_VIOLATED),
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errmsg("triggered_change_notification: must not be called with more than one parameter")));
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if (nargs == 0)
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channel = "tcn";
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else
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channel = trigger->tgargs[0];
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/* get tuple data */
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trigtuple = trigdata->tg_trigtuple;
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rel = trigdata->tg_relation;
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tupdesc = rel->rd_att;
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foundPK = false;
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/*
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* Get the list of index OIDs for the table from the relcache, and look up
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* each one in the pg_index syscache until we find one marked primary key
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* (hopefully there isn't more than one such).
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*/
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indexoidlist = RelationGetIndexList(rel);
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foreach(indexoidscan, indexoidlist)
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{
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Oid indexoid = lfirst_oid(indexoidscan);
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HeapTuple indexTuple;
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Form_pg_index index;
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indexTuple = SearchSysCache1(INDEXRELID, ObjectIdGetDatum(indexoid));
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if (!HeapTupleIsValid(indexTuple)) /* should not happen */
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elog(ERROR, "cache lookup failed for index %u", indexoid);
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index = (Form_pg_index) GETSTRUCT(indexTuple);
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/* we're only interested if it is the primary key */
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if (index->indisprimary)
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{
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int numatts = index->indnatts;
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if (numatts > 0)
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{
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int i;
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foundPK = true;
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strcpy_quoted(payload, RelationGetRelationName(rel), '"');
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appendStringInfoCharMacro(payload, ',');
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appendStringInfoCharMacro(payload, operation);
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for (i = 0; i < numatts; i++)
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{
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int colno = index->indkey.values[i];
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appendStringInfoCharMacro(payload, ',');
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strcpy_quoted(payload, NameStr((tupdesc->attrs[colno - 1])->attname), '"');
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appendStringInfoCharMacro(payload, '=');
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strcpy_quoted(payload, SPI_getvalue(trigtuple, tupdesc, colno), '\'');
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}
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Async_Notify(channel, payload->data);
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}
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ReleaseSysCache(indexTuple);
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break;
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}
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ReleaseSysCache(indexTuple);
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}
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list_free(indexoidlist);
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if (!foundPK)
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ereport(ERROR,
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(errcode(ERRCODE_E_R_I_E_TRIGGER_PROTOCOL_VIOLATED),
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errmsg("triggered_change_notification: must be called on a table with a primary key")));
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return PointerGetDatum(NULL); /* after trigger; value doesn't matter */
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}

‎contrib/tcn/tcn.control

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# tcn extension
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comment = 'Triggered change notifications'
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default_version = '1.0'
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module_pathname = '$libdir/tcn'
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relocatable = true

‎doc/src/sgml/contrib.sgml

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@@ -128,6 +128,7 @@ CREATE EXTENSION <replaceable>module_name</> FROM unpackaged;
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&contrib-spi;
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&sslinfo;
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&tablefunc;
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&tcn;
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&test-parser;
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&tsearch2;
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&unaccent;

‎doc/src/sgml/filelist.sgml

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<!ENTITY sepgsql SYSTEM "sepgsql.sgml">
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<!ENTITY sslinfo SYSTEM "sslinfo.sgml">
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<!ENTITY tablefunc SYSTEM "tablefunc.sgml">
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<!ENTITY tcn SYSTEM "tcn.sgml">
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<!ENTITY test-parser SYSTEM "test-parser.sgml">
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<!ENTITY tsearch2 SYSTEM "tsearch2.sgml">
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<!ENTITY unaccent SYSTEM "unaccent.sgml">

‎doc/src/sgml/tcn.sgml

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<!-- doc/src/sgml/tcn.sgml -->
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<sect1 id="tcn" xreflabel="tcn">
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<title>tcn</title>
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<indexterm zone="tcn">
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<primary>tcn</primary>
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</indexterm>
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<indexterm zone="tcn">
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<primary>triggered_change_notification</primary>
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</indexterm>
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<para>
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The <filename>tcn</> module provides a trigger function that notifies
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listeners of changes to any table on which it is attached. It must be
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used as an <literal>AFTER</> trigger <literal>FOR EACH ROW</>.
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</para>
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<para>
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Only one parameter may be suupplied to the function in a
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<literal>CREATE TRIGGER</> statement, and that is optional. If supplied
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it will be used for the channel name for the notifications. If omitted
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<literal>tcn</> will be used for the channel name.
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</para>
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<para>
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The payload of the notifications consists of the table name, a letter to
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indicate which type of operation was performed, and column name/value pairs
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for primary key columns. Each part is separated from the next by a comma.
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For ease of parsing using regular expressions, table and column names are
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always wrapped in double quotes, and data values are always wrapped in
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single quotes. Embeded quotes are doubled.
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</para>
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<para>
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A brief example of using the extension follows.
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<programlisting>
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test=# create table tcndata
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test-# (
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test(# a int not null,
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test(# b date not null,
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test(# c text,
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test(# primary key (a, b)
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test(# );
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NOTICE: CREATE TABLE / PRIMARY KEY will create implicit index "tcndata_pkey" for table "tcndata"
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CREATE TABLE
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test=# create trigger tcndata_tcn_trigger
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test-# after insert or update or delete on tcndata
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test-# for each row execute procedure triggered_change_notification();
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CREATE TRIGGER
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test=# listen tcn;
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LISTEN
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test=# insert into tcndata values (1, date '2012-12-22', 'one'),
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test-# (1, date '2012-12-23', 'another'),
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test-# (2, date '2012-12-23', 'two');
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INSERT 0 3
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Asynchronous notification "tcn" with payload ""tcndata",I,"a"='1',"b"='2012-12-22'" received from server process with PID 22770.
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Asynchronous notification "tcn" with payload ""tcndata",I,"a"='1',"b"='2012-12-23'" received from server process with PID 22770.
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Asynchronous notification "tcn" with payload ""tcndata",I,"a"='2',"b"='2012-12-23'" received from server process with PID 22770.
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test=# update tcndata set c = 'uno' where a = 1;
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UPDATE 2
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Asynchronous notification "tcn" with payload ""tcndata",U,"a"='1',"b"='2012-12-22'" received from server process with PID 22770.
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Asynchronous notification "tcn" with payload ""tcndata",U,"a"='1',"b"='2012-12-23'" received from server process with PID 22770.
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test=# delete from tcndata where a = 1 and b = date '2012-12-22';
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DELETE 1
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Asynchronous notification "tcn" with payload ""tcndata",D,"a"='1',"b"='2012-12-22'" received from server process with PID 22770.
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</programlisting>
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</para>
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</sect1>

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