Refactor the executor's API to support data-modifying CTEs better.

The originally committed patch for modifying CTEs didn't interact well
with EXPLAIN, as noted by myself, and also had corner-case problems with
triggers, as noted by Dean Rasheed.  Those problems show it is really not
practical for ExecutorEnd to call any user-defined code; so split the
cleanup duties out into a new function ExecutorFinish, which must be called
between the last ExecutorRun call and ExecutorEnd.  Some Asserts have been
added to these functions to help verify correct usage.

It is no longer necessary for callers of the executor to call
AfterTriggerBeginQuery/AfterTriggerEndQuery for themselves, as this is now
done by ExecutorStart/ExecutorFinish respectively.  If you really need to
suppress that and do it for yourself, pass EXEC_FLAG_SKIP_TRIGGERS to
ExecutorStart.

Also, refactor portal commit processing to allow for the possibility that
PortalDrop will invoke user-defined code.  I think this is not actually
necessary just yet, since the portal-execution-strategy logic forces any
non-pure-SELECT query to be run to completion before we will consider
committing.  But it seems like good future-proofing.

1 files changed, 28 insertions, 0 deletions

diff --git a/contrib/pg_stat_statements/pg_stat_statements.c b/contrib/pg_stat_statements/pg_stat_statements.c
index c361c7a86c2..0390ec4c8ed 100644
--- a/contrib/pg_stat_statements/pg_stat_statements.c
+++ b/contrib/pg_stat_statements/pg_stat_statements.c
@@ -122,6 +122,7 @@ static int	nested_level = 0;
 static shmem_startup_hook_type prev_shmem_startup_hook = NULL;
 static ExecutorStart_hook_type prev_ExecutorStart = NULL;
 static ExecutorRun_hook_type prev_ExecutorRun = NULL;
+static ExecutorFinish_hook_type prev_ExecutorFinish = NULL;
 static ExecutorEnd_hook_type prev_ExecutorEnd = NULL;
 static ProcessUtility_hook_type prev_ProcessUtility = NULL;
 
@@ -173,6 +174,7 @@ static void pgss_ExecutorStart(QueryDesc *queryDesc, int eflags);
 static void pgss_ExecutorRun(QueryDesc *queryDesc,
 				 ScanDirection direction,
 				 long count);
+static void pgss_ExecutorFinish(QueryDesc *queryDesc);
 static void pgss_ExecutorEnd(QueryDesc *queryDesc);
 static void pgss_ProcessUtility(Node *parsetree,
 			  const char *queryString, ParamListInfo params, bool isTopLevel,
@@ -269,6 +271,8 @@ _PG_init(void)
 	ExecutorStart_hook = pgss_ExecutorStart;
 	prev_ExecutorRun = ExecutorRun_hook;
 	ExecutorRun_hook = pgss_ExecutorRun;
+	prev_ExecutorFinish = ExecutorFinish_hook;
+	ExecutorFinish_hook = pgss_ExecutorFinish;
 	prev_ExecutorEnd = ExecutorEnd_hook;
 	ExecutorEnd_hook = pgss_ExecutorEnd;
 	prev_ProcessUtility = ProcessUtility_hook;
@@ -285,6 +289,7 @@ _PG_fini(void)
 	shmem_startup_hook = prev_shmem_startup_hook;
 	ExecutorStart_hook = prev_ExecutorStart;
 	ExecutorRun_hook = prev_ExecutorRun;
+	ExecutorFinish_hook = prev_ExecutorFinish;
 	ExecutorEnd_hook = prev_ExecutorEnd;
 	ProcessUtility_hook = prev_ProcessUtility;
 }
@@ -550,6 +555,29 @@ pgss_ExecutorRun(QueryDesc *queryDesc, ScanDirection direction, long count)
 }
 
 /*
+ * ExecutorFinish hook: all we need do is track nesting depth
+ */
+static void
+pgss_ExecutorFinish(QueryDesc *queryDesc)
+{
+	nested_level++;
+	PG_TRY();
+	{
+		if (prev_ExecutorFinish)
+			prev_ExecutorFinish(queryDesc);
+		else
+			standard_ExecutorFinish(queryDesc);
+		nested_level--;
+	}
+	PG_CATCH();
+	{
+		nested_level--;
+		PG_RE_THROW();
+	}
+	PG_END_TRY();
+}
+
+/*
  * ExecutorEnd hook: store results if needed
  */
 static void