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Triggered change notifications. 

Kevin Grittner, reviewed (in earlier versions) by Álvaro Herrera
This commit is contained in:
Robert Haas 2012-01-19 23:15:15 -05:00
parent c8397bd6d9
commit 6e3323d41d
8 changed files with 290 additions and 0 deletions
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1
contrib/Makefile
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@ -45,6 +45,7 @@ SUBDIRS = \
seg \
spi \
tablefunc \
tcn \
test_parser \
tsearch2 \
unaccent \

17
contrib/tcn/Makefile Normal file
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@ -0,0 +1,17 @@
# contrib/tcn/Makefile
MODULES = tcn
EXTENSION = tcn
DATA = tcn--1.0.sql
ifdef USE_PGXS
PG_CONFIG = pg_config
PGXS := $(shell $(PG_CONFIG) --pgxs)
include $(PGXS)
else
subdir = contrib/tcn
top_builddir = ../..
include $(top_builddir)/src/Makefile.global
include $(top_srcdir)/contrib/contrib-global.mk
endif

9
contrib/tcn/tcn--1.0.sql Normal file
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@ -0,0 +1,9 @@
/* contrib/tcn/tcn--1.0.sql */
-- complain if script is sourced in psql, rather than via CREATE EXTENSION
\echo Use "CREATE EXTENSION tcn" to load this file. \quit
CREATE FUNCTION triggered_change_notification()
RETURNS pg_catalog.trigger
AS 'MODULE_PATHNAME'
LANGUAGE C;

184
contrib/tcn/tcn.c Normal file
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@ -0,0 +1,184 @@
/*-------------------------------------------------------------------------
*
* tcn.c
* triggered change notification support for PostgreSQL
*
* Portions Copyright (c) 2011-2012, PostgreSQL Global Development Group
* Portions Copyright (c) 1994, Regents of the University of California
*
*
* IDENTIFICATION
* contrib/tcn/tcn.c
*
*-------------------------------------------------------------------------
*/
#include "postgres.h"
#include "executor/spi.h"
#include "commands/async.h"
#include "commands/trigger.h"
#include "lib/stringinfo.h"
#include "utils/rel.h"
#include "utils/syscache.h"
PG_MODULE_MAGIC;
/* forward declarations */
Datum triggered_change_notification(PG_FUNCTION_ARGS);
/*
* Copy from s (for source) to r (for result), wrapping with q (quote)
* characters and doubling any quote characters found.
*/
static void
strcpy_quoted(StringInfo r, const char *s, const char q)
{
appendStringInfoCharMacro(r, q);
while (*s)
{
if (*s == q)
appendStringInfoCharMacro(r, q);
appendStringInfoCharMacro(r, *s);
s++;
}
appendStringInfoCharMacro(r, q);
}
/*
* triggered_change_notification
*
* This trigger function will send a notification of data modification with
* primary key values. The channel will be "tcn" unless the trigger is
* created with a parameter, in which case that parameter will be used.
*/
PG_FUNCTION_INFO_V1(triggered_change_notification);
Datum
triggered_change_notification(PG_FUNCTION_ARGS)
{
TriggerData *trigdata = (TriggerData *) fcinfo->context;
Trigger *trigger;
int nargs;
HeapTuple trigtuple;
Relation rel;
TupleDesc tupdesc;
char *channel;
char operation;
StringInfo payload = makeStringInfo();
bool foundPK;
List *indexoidlist;
ListCell *indexoidscan;
/* make sure it's called as a trigger */
if (!CALLED_AS_TRIGGER(fcinfo))
ereport(ERROR,
(errcode(ERRCODE_E_R_I_E_TRIGGER_PROTOCOL_VIOLATED),
errmsg("triggered_change_notification: must be called as trigger")));
/* and that it's called after the change */
if (!TRIGGER_FIRED_AFTER(trigdata->tg_event))
ereport(ERROR,
(errcode(ERRCODE_E_R_I_E_TRIGGER_PROTOCOL_VIOLATED),
errmsg("triggered_change_notification: must be called after the change")));
/* and that it's called for each row */
if (!TRIGGER_FIRED_FOR_ROW(trigdata->tg_event))
ereport(ERROR,
(errcode(ERRCODE_E_R_I_E_TRIGGER_PROTOCOL_VIOLATED),
errmsg("triggered_change_notification: must be called for each row")));
if (TRIGGER_FIRED_BY_INSERT(trigdata->tg_event))
operation = 'I';
else if (TRIGGER_FIRED_BY_UPDATE(trigdata->tg_event))
operation = 'U';
else if (TRIGGER_FIRED_BY_DELETE(trigdata->tg_event))
operation = 'D';
else
{
elog(ERROR, "triggered_change_notification: trigger fired by unrecognized operation");
operation = 'X'; /* silence compiler warning */
}
trigger = trigdata->tg_trigger;
nargs = trigger->tgnargs;
if (nargs > 1)
ereport(ERROR,
(errcode(ERRCODE_E_R_I_E_TRIGGER_PROTOCOL_VIOLATED),
errmsg("triggered_change_notification: must not be called with more than one parameter")));
if (nargs == 0)
channel = "tcn";
else
channel = trigger->tgargs[0];
/* get tuple data */
trigtuple = trigdata->tg_trigtuple;
rel = trigdata->tg_relation;
tupdesc = rel->rd_att;
foundPK = false;
/*
* Get the list of index OIDs for the table from the relcache, and look up
* each one in the pg_index syscache until we find one marked primary key
* (hopefully there isn't more than one such).
*/
indexoidlist = RelationGetIndexList(rel);
foreach(indexoidscan, indexoidlist)
{
Oid indexoid = lfirst_oid(indexoidscan);
HeapTuple indexTuple;
Form_pg_index index;
indexTuple = SearchSysCache1(INDEXRELID, ObjectIdGetDatum(indexoid));
if (!HeapTupleIsValid(indexTuple)) /* should not happen */
elog(ERROR, "cache lookup failed for index %u", indexoid);
index = (Form_pg_index) GETSTRUCT(indexTuple);
/* we're only interested if it is the primary key */
if (index->indisprimary)
{
int numatts = index->indnatts;
if (numatts > 0)
{
int i;
foundPK = true;
strcpy_quoted(payload, RelationGetRelationName(rel), '"');
appendStringInfoCharMacro(payload, ',');
appendStringInfoCharMacro(payload, operation);
for (i = 0; i < numatts; i++)
{
int colno = index->indkey.values[i];
appendStringInfoCharMacro(payload, ',');
strcpy_quoted(payload, NameStr((tupdesc->attrs[colno - 1])->attname), '"');
appendStringInfoCharMacro(payload, '=');
strcpy_quoted(payload, SPI_getvalue(trigtuple, tupdesc, colno), '\'');
}
Async_Notify(channel, payload->data);
}
ReleaseSysCache(indexTuple);
break;
}
ReleaseSysCache(indexTuple);
}
list_free(indexoidlist);
if (!foundPK)
ereport(ERROR,
(errcode(ERRCODE_E_R_I_E_TRIGGER_PROTOCOL_VIOLATED),
errmsg("triggered_change_notification: must be called on a table with a primary key")));
return PointerGetDatum(NULL); /* after trigger; value doesn't matter */
}

5
contrib/tcn/tcn.control Normal file
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@ -0,0 +1,5 @@
# tcn extension
comment = 'Triggered change notifications'
default_version = '1.0'
module_pathname = '$libdir/tcn'
relocatable = true

1
doc/src/sgml/contrib.sgml
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@ -128,6 +128,7 @@ CREATE EXTENSION <replaceable>module_name</> FROM unpackaged;
&contrib-spi;
&sslinfo;
&tablefunc;
&tcn;
&test-parser;
&tsearch2;
&unaccent;

1
doc/src/sgml/filelist.sgml
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@ -136,6 +136,7 @@
<!ENTITY sepgsql SYSTEM "sepgsql.sgml">
<!ENTITY sslinfo SYSTEM "sslinfo.sgml">
<!ENTITY tablefunc SYSTEM "tablefunc.sgml">
<!ENTITY tcn SYSTEM "tcn.sgml">
<!ENTITY test-parser SYSTEM "test-parser.sgml">
<!ENTITY tsearch2 SYSTEM "tsearch2.sgml">
<!ENTITY unaccent SYSTEM "unaccent.sgml">

72
doc/src/sgml/tcn.sgml Normal file
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@ -0,0 +1,72 @@
<!-- doc/src/sgml/tcn.sgml -->
<sect1 id="tcn" xreflabel="tcn">
<title>tcn</title>
<indexterm zone="tcn">
<primary>tcn</primary>
</indexterm>
<indexterm zone="tcn">
<primary>triggered_change_notification</primary>
</indexterm>
<para>
The <filename>tcn</> module provides a trigger function that notifies
listeners of changes to any table on which it is attached. It must be
used as an <literal>AFTER</> trigger <literal>FOR EACH ROW</>.
</para>
<para>
Only one parameter may be suupplied to the function in a
<literal>CREATE TRIGGER</> statement, and that is optional. If supplied
it will be used for the channel name for the notifications. If omitted
<literal>tcn</> will be used for the channel name.
</para>
<para>
The payload of the notifications consists of the table name, a letter to
indicate which type of operation was performed, and column name/value pairs
for primary key columns. Each part is separated from the next by a comma.
For ease of parsing using regular expressions, table and column names are
always wrapped in double quotes, and data values are always wrapped in
single quotes. Embeded quotes are doubled.
</para>
<para>
A brief example of using the extension follows.
<programlisting>
test=# create table tcndata
test-# (
test(# a int not null,
test(# b date not null,
test(# c text,
test(# primary key (a, b)
test(# );
NOTICE: CREATE TABLE / PRIMARY KEY will create implicit index "tcndata_pkey" for table "tcndata"
CREATE TABLE
test=# create trigger tcndata_tcn_trigger
test-# after insert or update or delete on tcndata
test-# for each row execute procedure triggered_change_notification();
CREATE TRIGGER
test=# listen tcn;
LISTEN
test=# insert into tcndata values (1, date '2012-12-22', 'one'),
test-# (1, date '2012-12-23', 'another'),
test-# (2, date '2012-12-23', 'two');
INSERT 0 3
Asynchronous notification "tcn" with payload ""tcndata",I,"a"='1',"b"='2012-12-22'" received from server process with PID 22770.
Asynchronous notification "tcn" with payload ""tcndata",I,"a"='1',"b"='2012-12-23'" received from server process with PID 22770.
Asynchronous notification "tcn" with payload ""tcndata",I,"a"='2',"b"='2012-12-23'" received from server process with PID 22770.
test=# update tcndata set c = 'uno' where a = 1;
UPDATE 2
Asynchronous notification "tcn" with payload ""tcndata",U,"a"='1',"b"='2012-12-22'" received from server process with PID 22770.
Asynchronous notification "tcn" with payload ""tcndata",U,"a"='1',"b"='2012-12-23'" received from server process with PID 22770.
test=# delete from tcndata where a = 1 and b = date '2012-12-22';
DELETE 1
Asynchronous notification "tcn" with payload ""tcndata",D,"a"='1',"b"='2012-12-22'" received from server process with PID 22770.
</programlisting>
</para>
</sect1>