Follow-on cleanup for the transition table patch.

Commit 5970271 added transition table support to PL/pgsql so that
SQL queries in trigger functions could access those transient
tables.  In order to provide the same level of support for PL/perl,
PL/python and PL/tcl, refactor the relevant code into a new
function SPI_register_trigger_data.  Call the new function in the
trigger handler of all four PLs, and document it as a public SPI
function so that authors of out-of-tree PLs can do the same.

Also get rid of a second QueryEnvironment object that was
maintained by PL/pgsql.  That was previously used to deal with
cursors, but the same approach wasn't appropriate for PLs that are
less tangled up with core code.  Instead, have SPI_cursor_open
install the connection's current QueryEnvironment, as already
happens for SPI_execute_plan.

While in the docs, remove the note that transition tables were only
supported in C and PL/pgSQL triggers, and correct some ommissions.

Thomas Munro with some work by Kevin Grittner (mostly docs)

Author: kgrittn

doc/src/sgml/ref/create_trigger.sgml

@@ -8,6 +8,11 @@ PostgreSQL documentation
   <primary>CREATE TRIGGER</primary>
  </indexterm>
 
+ <indexterm>
+  <primary>transition tables</primary>
+  <seealso>ephemeral named relation</seealso>
+ </indexterm>
+
  <refmeta>
   <refentrytitle>CREATE TRIGGER</refentrytitle>
   <manvolnum>7</manvolnum>
@@ -322,11 +327,6 @@ UPDATE OF <replaceable>column_name1</replaceable> [, <replaceable>column_name2</
      <para>
       The (unqualified) name to be used within the trigger for this relation.
      </para>
-     <note>
-      <para>
-       So far only triggers written in C or PL/pgSQL support this.
-      </para>
-     </note>
     </listitem>
    </varlistentry>
 

doc/src/sgml/spi.sgml

@@ -2644,6 +2644,11 @@ SPIPlanPtr SPI_saveplan(SPIPlanPtr <parameter>plan</parameter>)
 <refentry id="spi-spi-register-relation">
  <indexterm><primary>SPI_register_relation</primary></indexterm>
 
+ <indexterm>
+  <primary>ephemeral named relation</primary>
+  <secondary>registering with SPI</secondary>
+ </indexterm>
+
  <refmeta>
   <refentrytitle>SPI_register_relation</refentrytitle>
   <manvolnum>3</manvolnum>
@@ -2746,6 +2751,11 @@ int SPI_register_relation(EphemeralNamedRelation <parameter>enr</parameter>)
 <refentry id="spi-spi-unregister-relation">
  <indexterm><primary>SPI_unregister_relation</primary></indexterm>
 
+ <indexterm>
+  <primary>ephemeral named relation</primary>
+  <secondary>unregistering from SPI</secondary>
+ </indexterm>
+
  <refmeta>
   <refentrytitle>SPI_unregister_relation</refentrytitle>
   <manvolnum>3</manvolnum>
@@ -2843,6 +2853,121 @@ int SPI_unregister_relation(const char * <parameter>name</parameter>)
 
 <!-- *********************************************** -->
 
+<refentry id="spi-spi-register-trigger-data">
+ <indexterm><primary>SPI_register_trigger_data</primary></indexterm>
+
+ <indexterm>
+  <primary>ephemeral named relation</primary>
+  <secondary>registering with SPI</secondary>
+ </indexterm>
+
+ <indexterm>
+  <primary>transition tables</primary>
+  <secondary>implementation in PLs</secondary>
+ </indexterm>
+
+ <refmeta>
+  <refentrytitle>SPI_register_trigger_data</refentrytitle>
+  <manvolnum>3</manvolnum>
+ </refmeta>
+
+ <refnamediv>
+  <refname>SPI_register_trigger_data</refname>
+  <refpurpose>make ephemeral trigger data available in SPI queries</refpurpose>
+ </refnamediv>
+
+ <refsynopsisdiv>
+<synopsis>
+int SPI_register_trigger_data(TriggerData *<parameter>tdata</parameter>)
+</synopsis>
+ </refsynopsisdiv>
+
+ <refsect1>
+  <title>Description</title>
+
+  <para>
+   <function>SPI_register_trigger_data</function> makes any ephemeral
+   relations captured by a trigger available to queries planned and executed
+   through the current SPI connection.  Currently, this means the transition
+   tables captured by an <literal>AFTER</literal> trigger defined with a
+   <literal>REFERENCING OLD/NEW TABLE AS</literal> ... clause.  This function
+   should be called by a PL trigger handler function after connecting.
+  </para>
+ </refsect1>
+
+ <refsect1>
+  <title>Arguments</title>
+
+  <variablelist>
+   <varlistentry>
+    <term><literal>TriggerData *<parameter>tdata</parameter></literal></term>
+    <listitem>
+     <para>
+       the <structname>TriggerData</structname> object passed to a trigger
+       handler function as <literal>fcinfo->context</literal>
+     </para>
+    </listitem>
+   </varlistentry>
+  </variablelist>
+ </refsect1>
+
+ <refsect1>
+  <title>Return Value</title>
+
+  <para>
+   If the execution of the command was successful then the following
+   (nonnegative) value will be returned:
+
+   <variablelist>
+    <varlistentry>
+     <term><symbol>SPI_OK_TD_REGISTER</symbol></term>
+     <listitem>
+      <para>
+       if the captured trigger data (if any) has been successfully registered
+      </para>
+     </listitem>
+    </varlistentry>
+   </variablelist>
+  </para>
+
+  <para>
+   On error, one of the following negative values is returned:
+
+   <variablelist>
+    <varlistentry>
+     <term><symbol>SPI_ERROR_ARGUMENT</symbol></term>
+     <listitem>
+      <para>
+       if <parameter>tdata</parameter> is <symbol>NULL</symbol>
+      </para>
+     </listitem>
+    </varlistentry>
+
+    <varlistentry>
+     <term><symbol>SPI_ERROR_UNCONNECTED</symbol></term>
+     <listitem>
+      <para>
+       if called from an unconnected procedure
+      </para>
+     </listitem>
+    </varlistentry>
+
+    <varlistentry>
+     <term><symbol>SPI_ERROR_REL_DUPLICATE</symbol></term>
+     <listitem>
+      <para>
+       if the name of any trigger data transient relation is already
+       registered for this connection
+      </para>
+     </listitem>
+    </varlistentry>
+   </variablelist>
+  </para>
+ </refsect1>
+</refentry>
+
+<!-- *********************************************** -->
+
 </sect1>
 
 <sect1 id="spi-interface-support">

doc/src/sgml/trigger.sgml

@@ -395,6 +395,11 @@
     <secondary>in C</secondary>
    </indexterm>
 
+   <indexterm>
+    <primary>transition tables</primary>
+    <secondary>referencing from C trigger</secondary>
+   </indexterm>
+
    <para>
     This section describes the low-level details of the interface to a
     trigger function.  This information is only needed when writing
@@ -438,14 +443,16 @@ CALLED_AS_TRIGGER(fcinfo)
 <programlisting>
 typedef struct TriggerData
 {
-    NodeTag       type;
-    TriggerEvent  tg_event;
-    Relation      tg_relation;
-    HeapTuple     tg_trigtuple;
-    HeapTuple     tg_newtuple;
-    Trigger      *tg_trigger;
-    Buffer        tg_trigtuplebuf;
-    Buffer        tg_newtuplebuf;
+    NodeTag          type;
+    TriggerEvent     tg_event;
+    Relation         tg_relation;
+    HeapTuple        tg_trigtuple;
+    HeapTuple        tg_newtuple;
+    Trigger         *tg_trigger;
+    Buffer           tg_trigtuplebuf;
+    Buffer           tg_newtuplebuf;
+    Tuplestorestate *tg_oldtable;
+    Tuplestorestate *tg_newtable;
 } TriggerData;
 </programlisting>
 
@@ -629,6 +636,8 @@ typedef struct Trigger
     int16      *tgattr;
     char      **tgargs;
     char       *tgqual;
+    char       *tgoldtable;
+    char       *tgnewtable;
 } Trigger;
 </programlisting>
 
@@ -662,9 +671,38 @@ typedef struct Trigger
       </listitem>
      </varlistentry>
 
+     <varlistentry>
+      <term><structfield>tg_oldtable</></term>
+      <listitem>
+       <para>
+        A pointer to a structure of type <structname>Tuplestorestate</structname>
+        containing zero or more rows in the format specified by
+        <structfield>tg_relation</structfield>, or a <symbol>NULL</> pointer
+        if there is no <literal>OLD TABLE</literal> transition relation.
+       </para>
+      </listitem>
+     </varlistentry>
+
+     <varlistentry>
+      <term><structfield>tg_newtable</></term>
+      <listitem>
+       <para>
+        A pointer to a structure of type <structname>Tuplestorestate</structname>
+        containing zero or more rows in the format specified by
+        <structfield>tg_relation</structfield>, or a <symbol>NULL</> pointer
+        if there is no <literal>NEW TABLE</literal> transition relation.
+       </para>
+      </listitem>
+     </varlistentry>
+
     </variablelist>
    </para>
 
+   <para>
+    To allow queries issued through SPI to reference transition tables, see
+    <xref linkend="spi-spi-register-trigger-data">.
+   </para>
+
    <para>
     A trigger function must return either a
     <structname>HeapTuple</> pointer or a <symbol>NULL</> pointer

src/backend/executor/spi.c

@@ -1257,6 +1257,9 @@ SPI_cursor_open_internal(const char *name, SPIPlanPtr plan,
 					 errdetail("Scrollable cursors must be READ ONLY.")));
 	}
 
+	/* Make current query environment available to portal at execution time. */
+	portal->queryEnv = _SPI_current->queryEnv;
+
 	/*
 	 * If told to be read-only, or in parallel mode, verify that this query is
 	 * in fact read-only.  This can't be done earlier because we need to look
@@ -2716,3 +2719,52 @@ SPI_unregister_relation(const char *name)
 
 	return res;
 }
+
+/*
+ * Register the transient relations from 'tdata' using this SPI connection.
+ * This should be called by PL implementations' trigger handlers after
+ * connecting, in order to make transition tables visible to any queries run
+ * in this connection.
+ */
+int
+SPI_register_trigger_data(TriggerData *tdata)
+{
+	if (tdata == NULL)
+		return SPI_ERROR_ARGUMENT;
+
+	if (tdata->tg_newtable)
+	{
+		EphemeralNamedRelation enr =
+			palloc(sizeof(EphemeralNamedRelationData));
+		int		rc;
+
+		enr->md.name = tdata->tg_trigger->tgnewtable;
+		enr->md.reliddesc = tdata->tg_relation->rd_id;
+		enr->md.tupdesc = NULL;
+		enr->md.enrtype = ENR_NAMED_TUPLESTORE;
+		enr->md.enrtuples = tuplestore_tuple_count(tdata->tg_newtable);
+		enr->reldata = tdata->tg_newtable;
+		rc = SPI_register_relation(enr);
+		if (rc != SPI_OK_REL_REGISTER)
+			return rc;
+	}
+
+	if (tdata->tg_oldtable)
+	{
+		EphemeralNamedRelation enr =
+			palloc(sizeof(EphemeralNamedRelationData));
+		int		rc;
+
+		enr->md.name = tdata->tg_trigger->tgoldtable;
+		enr->md.reliddesc = tdata->tg_relation->rd_id;
+		enr->md.tupdesc = NULL;
+		enr->md.enrtype = ENR_NAMED_TUPLESTORE;
+		enr->md.enrtuples = tuplestore_tuple_count(tdata->tg_oldtable);
+		enr->reldata = tdata->tg_oldtable;
+		rc = SPI_register_relation(enr);
+		if (rc != SPI_OK_REL_REGISTER)
+			return rc;
+	}
+
+	return SPI_OK_TD_REGISTER;
+}

src/include/executor/spi.h

@@ -13,6 +13,7 @@
 #ifndef SPI_H
 #define SPI_H
 
+#include "commands/trigger.h"
 #include "lib/ilist.h"
 #include "nodes/parsenodes.h"
 #include "utils/portal.h"
@@ -62,6 +63,7 @@ typedef struct _SPI_plan *SPIPlanPtr;
 #define SPI_OK_REWRITTEN		14
 #define SPI_OK_REL_REGISTER		15
 #define SPI_OK_REL_UNREGISTER	16
+#define SPI_OK_TD_REGISTER		17
 
 /* These used to be functions, now just no-ops for backwards compatibility */
 #define SPI_push()	((void) 0)
@@ -152,6 +154,7 @@ extern void SPI_cursor_close(Portal portal);
 
 extern int SPI_register_relation(EphemeralNamedRelation enr);
 extern int SPI_unregister_relation(const char *name);
+extern int SPI_register_trigger_data(TriggerData *tdata);
 
 extern void AtEOXact_SPI(bool isCommit);
 extern void AtEOSubXact_SPI(bool isCommit, SubTransactionId mySubid);

src/pl/plperl/expected/plperl_trigger.out

@@ -241,6 +241,35 @@ $$ LANGUAGE plperl;
 SELECT direct_trigger();
 ERROR:  trigger functions can only be called as triggers
 CONTEXT:  compilation of PL/Perl function "direct_trigger"
+-- check that SQL run in trigger code can see transition tables
+CREATE TABLE transition_table_test (id int, name text);
+INSERT INTO transition_table_test VALUES (1, 'a');
+CREATE FUNCTION transition_table_test_f() RETURNS trigger LANGUAGE plperl AS
+$$
+    my $cursor = spi_query("SELECT * FROM old_table");
+    my $row = spi_fetchrow($cursor);
+    defined($row) || die "expected a row";
+    elog(INFO, "old: " . $row->{id} . " -> " . $row->{name});
+    my $row = spi_fetchrow($cursor);
+    !defined($row) || die "expected no more rows";
+
+    my $cursor = spi_query("SELECT * FROM new_table");
+    my $row = spi_fetchrow($cursor);
+    defined($row) || die "expected a row";
+    elog(INFO, "new: " . $row->{id} . " -> " . $row->{name});
+    my $row = spi_fetchrow($cursor);
+    !defined($row) || die "expected no more rows";
+
+    return undef;
+$$;
+CREATE TRIGGER a_t AFTER UPDATE ON transition_table_test
+  REFERENCING OLD TABLE AS old_table NEW TABLE AS new_table
+  FOR EACH STATEMENT EXECUTE PROCEDURE transition_table_test_f();
+UPDATE transition_table_test SET name = 'b';
+INFO:  old: 1 -> a
+INFO:  new: 1 -> b
+DROP TABLE transition_table_test;
+DROP FUNCTION transition_table_test_f();
 -- test plperl command triggers
 create or replace function perlsnitch() returns event_trigger language plperl as $$
   elog(NOTICE, "perlsnitch: " . $_TD->{event} . " " . $_TD->{tag} . " ");

src/pl/plperl/plperl.c

@@ -2442,11 +2442,18 @@ plperl_trigger_handler(PG_FUNCTION_ARGS)
 	SV		   *svTD;
 	HV		   *hvTD;
 	ErrorContextCallback pl_error_context;
+	TriggerData *tdata;
+	int 		rc PG_USED_FOR_ASSERTS_ONLY;
 
 	/* Connect to SPI manager */
 	if (SPI_connect() != SPI_OK_CONNECT)
 		elog(ERROR, "could not connect to SPI manager");
 
+	/* Make transition tables visible to this SPI connection */
+	tdata = (TriggerData *) fcinfo->context;
+	rc = SPI_register_trigger_data(tdata);
+	Assert(rc >= 0);
+
 	/* Find or compile the function */
 	prodesc = compile_plperl_function(fcinfo->flinfo->fn_oid, true, false);
 	current_call_data->prodesc = prodesc;