Add tg_updatedcols to TriggerData

This allows a trigger function to determine for an UPDATE trigger
which columns were actually updated.  This allows some optimizations
in generic trigger functions such as lo_manage and
tsvector_update_trigger.

Reviewed-by: Daniel Gustafsson <daniel@yesql.se>
Discussion: https://www.postgresql.org/message-id/flat/11c5f156-67a9-0fb5-8200-2a8018eb2e0c@2ndquadrant.com

Author: petere

contrib/lo/expected/lo.out

@@ -36,6 +36,14 @@ SELECT lo_get(43214);
  \x
 (1 row)
 
+-- test updating of unrelated column
+UPDATE image SET title = 'beautiful picture' WHERE title = 'beautiful image';
+SELECT lo_get(43214);
+ lo_get 
+--------
+ \x
+(1 row)
+
 DELETE FROM image;
 SELECT lo_get(43214);
 ERROR:  large object 43214 does not exist

contrib/lo/lo.c

@@ -74,7 +74,8 @@ lo_manage(PG_FUNCTION_ARGS)
 	 * Here, if the value of the monitored attribute changes, then the large
 	 * object associated with the original value is unlinked.
 	 */
-	if (newtuple != NULL)
+	if (newtuple != NULL &&
+		bms_is_member(attnum - FirstLowInvalidHeapAttributeNumber, trigdata->tg_updatedcols))
 	{
 		char	   *orig = SPI_getvalue(trigtuple, tupdesc, attnum);
 		char	   *newv = SPI_getvalue(newtuple, tupdesc, attnum);

contrib/lo/sql/lo.sql

@@ -18,6 +18,11 @@ UPDATE image SET raster = 43214 WHERE title = 'beautiful image';
 SELECT lo_get(43213);
 SELECT lo_get(43214);
 
+-- test updating of unrelated column
+UPDATE image SET title = 'beautiful picture' WHERE title = 'beautiful image';
+
+SELECT lo_get(43214);
+
 DELETE FROM image;
 
 SELECT lo_get(43214);

doc/src/sgml/trigger.sgml

@@ -517,6 +517,7 @@ typedef struct TriggerData
     TupleTableSlot  *tg_newslot;
     Tuplestorestate *tg_oldtable;
     Tuplestorestate *tg_newtable;
+    const Bitmapset *tg_updatedcols;
 } TriggerData;
 </programlisting>
 
@@ -759,6 +760,30 @@ typedef struct Trigger
       </listitem>
      </varlistentry>
 
+     <varlistentry>
+      <term><structfield>tg_updatedcols</structfield></term>
+      <listitem>
+       <para>
+        For <literal>UPDATE</literal> triggers, a bitmap set indicating the
+        columns that were updated by the triggering command.  Generic trigger
+        functions can use this to optimize actions by not having to deal with
+        columns that were not changed.
+       </para>
+
+       <para>
+        As an example, to determine whether a column with attribute number
+        <varname>attnum</varname> (1-based) is a member of this bitmap set,
+        call <literal>bms_is_member(attnum -
+        FirstLowInvalidHeapAttributeNumber,
+        trigdata->tg_updatedcols))</literal>.
+       </para>
+
+       <para>
+        For triggers other than <literal>UPDATE</literal> triggers, this will
+        be <symbol>NULL</symbol>.
+       </para>
+      </listitem>
+     </varlistentry>
     </variablelist>
    </para>
 

src/backend/commands/trigger.c

@@ -2591,6 +2591,7 @@ ExecBSUpdateTriggers(EState *estate, ResultRelInfo *relinfo)
 	LocTriggerData.tg_event = TRIGGER_EVENT_UPDATE |
 		TRIGGER_EVENT_BEFORE;
 	LocTriggerData.tg_relation = relinfo->ri_RelationDesc;
+	LocTriggerData.tg_updatedcols = updatedCols;
 	for (i = 0; i < trigdesc->numtriggers; i++)
 	{
 		Trigger    *trigger = &trigdesc->triggers[i];
@@ -2699,6 +2700,7 @@ ExecBRUpdateTriggers(EState *estate, EPQState *epqstate,
 		TRIGGER_EVENT_BEFORE;
 	LocTriggerData.tg_relation = relinfo->ri_RelationDesc;
 	updatedCols = GetAllUpdatedColumns(relinfo, estate);
+	LocTriggerData.tg_updatedcols = updatedCols;
 	for (i = 0; i < trigdesc->numtriggers; i++)
 	{
 		Trigger    *trigger = &trigdesc->triggers[i];
@@ -3255,6 +3257,7 @@ typedef struct AfterTriggerSharedData
 	Oid			ats_relid;		/* the relation it's on */
 	CommandId	ats_firing_id;	/* ID for firing cycle */
 	struct AfterTriggersTableData *ats_table;	/* transition table access */
+	Bitmapset  *ats_modifiedcols;	/* modified columns */
 } AfterTriggerSharedData;
 
 typedef struct AfterTriggerEventData *AfterTriggerEvent;
@@ -3954,6 +3957,8 @@ AfterTriggerExecute(EState *estate,
 	LocTriggerData.tg_event =
 		evtshared->ats_event & (TRIGGER_EVENT_OPMASK | TRIGGER_EVENT_ROW);
 	LocTriggerData.tg_relation = rel;
+	if (TRIGGER_FOR_UPDATE(LocTriggerData.tg_trigger->tgtype))
+		LocTriggerData.tg_updatedcols = evtshared->ats_modifiedcols;
 
 	MemoryContextReset(per_tuple_context);
 
@@ -5641,6 +5646,7 @@ AfterTriggerSaveEvent(EState *estate, ResultRelInfo *relinfo,
 			new_shared.ats_table = transition_capture->tcs_private;
 		else
 			new_shared.ats_table = NULL;
+		new_shared.ats_modifiedcols = modifiedCols;
 
 		afterTriggerAddEvent(&afterTriggers.query_stack[afterTriggers.query_depth].events,
 							 &new_event, &new_shared);

src/backend/utils/adt/tsvector_op.c

@@ -2416,6 +2416,7 @@ tsvector_update_trigger(PG_FUNCTION_ARGS, bool config_column)
 	bool		isnull;
 	text	   *txt;
 	Oid			cfgId;
+	bool		update_needed;
 
 	/* Check call context */
 	if (!CALLED_AS_TRIGGER(fcinfo)) /* internal error */
@@ -2428,9 +2429,15 @@ tsvector_update_trigger(PG_FUNCTION_ARGS, bool config_column)
 		elog(ERROR, "tsvector_update_trigger: must be fired BEFORE event");
 
 	if (TRIGGER_FIRED_BY_INSERT(trigdata->tg_event))
+	{
 		rettuple = trigdata->tg_trigtuple;
+		update_needed = true;
+	}
 	else if (TRIGGER_FIRED_BY_UPDATE(trigdata->tg_event))
+	{
 		rettuple = trigdata->tg_newtuple;
+		update_needed = false;	/* computed below */
+	}
 	else
 		elog(ERROR, "tsvector_update_trigger: must be fired for INSERT or UPDATE");
 
@@ -2518,6 +2525,9 @@ tsvector_update_trigger(PG_FUNCTION_ARGS, bool config_column)
 					 errmsg("column \"%s\" is not of a character type",
 							trigger->tgargs[i])));
 
+		if (bms_is_member(numattr - FirstLowInvalidHeapAttributeNumber, trigdata->tg_updatedcols))
+			update_needed = true;
+
 		datum = SPI_getbinval(rettuple, rel->rd_att, numattr, &isnull);
 		if (isnull)
 			continue;
@@ -2530,16 +2540,19 @@ tsvector_update_trigger(PG_FUNCTION_ARGS, bool config_column)
 			pfree(txt);
 	}
 
-	/* make tsvector value */
-	datum = TSVectorGetDatum(make_tsvector(&prs));
-	isnull = false;
+	if (update_needed)
+	{
+		/* make tsvector value */
+		datum = TSVectorGetDatum(make_tsvector(&prs));
+		isnull = false;
 
-	/* and insert it into tuple */
-	rettuple = heap_modify_tuple_by_cols(rettuple, rel->rd_att,
-										 1, &tsvector_attr_num,
-										 &datum, &isnull);
+		/* and insert it into tuple */
+		rettuple = heap_modify_tuple_by_cols(rettuple, rel->rd_att,
+											 1, &tsvector_attr_num,
+											 &datum, &isnull);
 
-	pfree(DatumGetPointer(datum));
+		pfree(DatumGetPointer(datum));
+	}
 
 	return PointerGetDatum(rettuple);
 }

src/include/commands/trigger.h

@@ -39,6 +39,7 @@ typedef struct TriggerData
 	TupleTableSlot *tg_newslot;
 	Tuplestorestate *tg_oldtable;
 	Tuplestorestate *tg_newtable;
+	const Bitmapset *tg_updatedcols;
 } TriggerData;
 
 /*