Add pg_trigger_depth() function

This reports the depth level of triggers currently in execution, or zero
if not called from inside a trigger.

No catversion bump in this patch, but you have to initdb if you want
access to the new function.

Author: Kevin Grittner

doc/src/sgml/func.sgml

@@ -12794,6 +12794,13 @@ postgres=# SELECT * FROM unnest2(ARRAY[[1,2],[3,4]]);
        <entry>server start time</entry>
       </row>
 
+      <row>
+       <entry><literal><function>pg_trigger_depth()</function></literal></entry>
+       <entry><type>int</type></entry>
+       <entry>current nesting level of <productname>PostgreSQL</> triggers
+       (0 if not called, directly or indirectly, from inside a trigger)</entry>
+      </row>
+
       <row>
        <entry><literal><function>session_user</function></literal></entry>
        <entry><type>name</type></entry>

src/backend/commands/trigger.c

@@ -59,6 +59,8 @@
 /* GUC variables */
 int			SessionReplicationRole = SESSION_REPLICATION_ROLE_ORIGIN;
 
+/* How many levels deep into trigger execution are we? */
+static int	MyTriggerDepth = 0;
 
 #define GetModifiedColumns(relinfo, estate) \
 	(rt_fetch((relinfo)->ri_RangeTableIndex, (estate)->es_range_table)->modifiedCols)
@@ -1838,7 +1840,18 @@ ExecCallTriggerFunc(TriggerData *trigdata,
 
 	pgstat_init_function_usage(&fcinfo, &fcusage);
 
-	result = FunctionCallInvoke(&fcinfo);
+	MyTriggerDepth++;
+	PG_TRY();
+	{
+		result = FunctionCallInvoke(&fcinfo);
+	}
+	PG_CATCH();
+	{
+		MyTriggerDepth--;
+		PG_RE_THROW();
+	}
+	PG_END_TRY();
+	MyTriggerDepth--;
 
 	pgstat_end_function_usage(&fcusage, true);
 
@@ -4632,3 +4645,9 @@ AfterTriggerSaveEvent(EState *estate, ResultRelInfo *relinfo,
 							 &new_event, &new_shared);
 	}
 }
+
+Datum
+pg_trigger_depth(PG_FUNCTION_ARGS)
+{
+	PG_RETURN_INT32(MyTriggerDepth);
+}

src/include/catalog/pg_proc.h

@@ -2698,6 +2698,9 @@ DESCR("statistics: reset collected statistics for a single table or index in the
 DATA(insert OID = 3777 (  pg_stat_reset_single_function_counters	PGNSP PGUID 12 1 0 0 0 f f f f f v 1 0 2278 "26" _null_ _null_ _null_ _null_	pg_stat_reset_single_function_counters _null_ _null_ _null_ ));
 DESCR("statistics: reset collected statistics for a single function in the current database");
 
+DATA(insert OID = 3163 (  pg_trigger_depth				PGNSP PGUID 12 1 0 0 0 f f f t f s 0 0 23 "" _null_ _null_ _null_ _null_ pg_trigger_depth _null_ _null_ _null_ ));
+DESCR("current trigger depth");
+
 DATA(insert OID = 3778 ( pg_tablespace_location PGNSP PGUID 12 1 0 0 0 f f f t f s 1 0 25 "26" _null_ _null_ _null_ _null_ pg_tablespace_location _null_ _null_ _null_ ));
 DESCR("tablespace location");
 

src/include/commands/trigger.h

@@ -205,4 +205,6 @@ extern bool RI_Initial_Check(Trigger *trigger,
 
 extern int	RI_FKey_trigger_type(Oid tgfoid);
 
+extern Datum pg_trigger_depth(PG_FUNCTION_ARGS);
+
 #endif   /* TRIGGER_H */

src/test/regress/expected/triggers.out

@@ -1443,3 +1443,120 @@ NOTICE:  drop cascades to 2 other objects
 DETAIL:  drop cascades to view city_view
 drop cascades to view european_city_view
 DROP TABLE country_table;
+-- Test pg_trigger_depth()
+create table depth_a (id int not null primary key);
+NOTICE:  CREATE TABLE / PRIMARY KEY will create implicit index "depth_a_pkey" for table "depth_a"
+create table depth_b (id int not null primary key);
+NOTICE:  CREATE TABLE / PRIMARY KEY will create implicit index "depth_b_pkey" for table "depth_b"
+create table depth_c (id int not null primary key);
+NOTICE:  CREATE TABLE / PRIMARY KEY will create implicit index "depth_c_pkey" for table "depth_c"
+create function depth_a_tf() returns trigger
+  language plpgsql as $$
+begin
+  raise notice '%: depth = %', tg_name, pg_trigger_depth();
+  insert into depth_b values (new.id);
+  raise notice '%: depth = %', tg_name, pg_trigger_depth();
+  return new;
+end;
+$$;
+create trigger depth_a_tr before insert on depth_a
+  for each row execute procedure depth_a_tf();
+create function depth_b_tf() returns trigger
+  language plpgsql as $$
+begin
+  raise notice '%: depth = %', tg_name, pg_trigger_depth();
+  begin
+    execute 'insert into depth_c values (' || new.id::text || ')';
+  exception
+    when sqlstate 'U9999' then
+      raise notice 'SQLSTATE = U9999: depth = %', pg_trigger_depth();
+  end;
+  raise notice '%: depth = %', tg_name, pg_trigger_depth();
+  if new.id = 1 then
+    execute 'insert into depth_c values (' || new.id::text || ')';
+  end if;
+  return new;
+end;
+$$;
+create trigger depth_b_tr before insert on depth_b
+  for each row execute procedure depth_b_tf();
+create function depth_c_tf() returns trigger
+  language plpgsql as $$
+begin
+  raise notice '%: depth = %', tg_name, pg_trigger_depth();
+  if new.id = 1 then
+    raise exception sqlstate 'U9999';
+  end if;
+  raise notice '%: depth = %', tg_name, pg_trigger_depth();
+  return new;
+end;
+$$;
+create trigger depth_c_tr before insert on depth_c
+  for each row execute procedure depth_c_tf();
+select pg_trigger_depth();
+ pg_trigger_depth 
+------------------
+                0
+(1 row)
+
+insert into depth_a values (1);
+NOTICE:  depth_a_tr: depth = 1
+NOTICE:  depth_b_tr: depth = 2
+CONTEXT:  SQL statement "insert into depth_b values (new.id)"
+PL/pgSQL function "depth_a_tf" line 4 at SQL statement
+NOTICE:  depth_c_tr: depth = 3
+CONTEXT:  SQL statement "insert into depth_c values (1)"
+PL/pgSQL function "depth_b_tf" line 5 at EXECUTE statement
+SQL statement "insert into depth_b values (new.id)"
+PL/pgSQL function "depth_a_tf" line 4 at SQL statement
+NOTICE:  SQLSTATE = U9999: depth = 2
+CONTEXT:  SQL statement "insert into depth_b values (new.id)"
+PL/pgSQL function "depth_a_tf" line 4 at SQL statement
+NOTICE:  depth_b_tr: depth = 2
+CONTEXT:  SQL statement "insert into depth_b values (new.id)"
+PL/pgSQL function "depth_a_tf" line 4 at SQL statement
+NOTICE:  depth_c_tr: depth = 3
+CONTEXT:  SQL statement "insert into depth_c values (1)"
+PL/pgSQL function "depth_b_tf" line 12 at EXECUTE statement
+SQL statement "insert into depth_b values (new.id)"
+PL/pgSQL function "depth_a_tf" line 4 at SQL statement
+ERROR:  U9999
+CONTEXT:  SQL statement "insert into depth_c values (1)"
+PL/pgSQL function "depth_b_tf" line 12 at EXECUTE statement
+SQL statement "insert into depth_b values (new.id)"
+PL/pgSQL function "depth_a_tf" line 4 at SQL statement
+select pg_trigger_depth();
+ pg_trigger_depth 
+------------------
+                0
+(1 row)
+
+insert into depth_a values (2);
+NOTICE:  depth_a_tr: depth = 1
+NOTICE:  depth_b_tr: depth = 2
+CONTEXT:  SQL statement "insert into depth_b values (new.id)"
+PL/pgSQL function "depth_a_tf" line 4 at SQL statement
+NOTICE:  depth_c_tr: depth = 3
+CONTEXT:  SQL statement "insert into depth_c values (2)"
+PL/pgSQL function "depth_b_tf" line 5 at EXECUTE statement
+SQL statement "insert into depth_b values (new.id)"
+PL/pgSQL function "depth_a_tf" line 4 at SQL statement
+NOTICE:  depth_c_tr: depth = 3
+CONTEXT:  SQL statement "insert into depth_c values (2)"
+PL/pgSQL function "depth_b_tf" line 5 at EXECUTE statement
+SQL statement "insert into depth_b values (new.id)"
+PL/pgSQL function "depth_a_tf" line 4 at SQL statement
+NOTICE:  depth_b_tr: depth = 2
+CONTEXT:  SQL statement "insert into depth_b values (new.id)"
+PL/pgSQL function "depth_a_tf" line 4 at SQL statement
+NOTICE:  depth_a_tr: depth = 1
+select pg_trigger_depth();
+ pg_trigger_depth 
+------------------
+                0
+(1 row)
+
+drop table depth_a, depth_b, depth_c;
+drop function depth_a_tf();
+drop function depth_b_tf();
+drop function depth_c_tf();

src/test/regress/sql/triggers.sql

@@ -961,3 +961,67 @@ SELECT * FROM city_view;
 
 DROP TABLE city_table CASCADE;
 DROP TABLE country_table;
+
+
+-- Test pg_trigger_depth()
+
+create table depth_a (id int not null primary key);
+create table depth_b (id int not null primary key);
+create table depth_c (id int not null primary key);
+
+create function depth_a_tf() returns trigger
+  language plpgsql as $$
+begin
+  raise notice '%: depth = %', tg_name, pg_trigger_depth();
+  insert into depth_b values (new.id);
+  raise notice '%: depth = %', tg_name, pg_trigger_depth();
+  return new;
+end;
+$$;
+create trigger depth_a_tr before insert on depth_a
+  for each row execute procedure depth_a_tf();
+
+create function depth_b_tf() returns trigger
+  language plpgsql as $$
+begin
+  raise notice '%: depth = %', tg_name, pg_trigger_depth();
+  begin
+    execute 'insert into depth_c values (' || new.id::text || ')';
+  exception
+    when sqlstate 'U9999' then
+      raise notice 'SQLSTATE = U9999: depth = %', pg_trigger_depth();
+  end;
+  raise notice '%: depth = %', tg_name, pg_trigger_depth();
+  if new.id = 1 then
+    execute 'insert into depth_c values (' || new.id::text || ')';
+  end if;
+  return new;
+end;
+$$;
+create trigger depth_b_tr before insert on depth_b
+  for each row execute procedure depth_b_tf();
+
+create function depth_c_tf() returns trigger
+  language plpgsql as $$
+begin
+  raise notice '%: depth = %', tg_name, pg_trigger_depth();
+  if new.id = 1 then
+    raise exception sqlstate 'U9999';
+  end if;
+  raise notice '%: depth = %', tg_name, pg_trigger_depth();
+  return new;
+end;
+$$;
+create trigger depth_c_tr before insert on depth_c
+  for each row execute procedure depth_c_tf();
+
+select pg_trigger_depth();
+insert into depth_a values (1);
+select pg_trigger_depth();
+insert into depth_a values (2);
+select pg_trigger_depth();
+
+drop table depth_a, depth_b, depth_c;
+drop function depth_a_tf();
+drop function depth_b_tf();
+drop function depth_c_tf();