Add a new system view, pg_prepared_statements, that can be used to

access information about the prepared statements that are available
in the current session. Original patch from Joachim Wieland, various
improvements by Neil Conway.

The "statement" column of the view contains the literal query string
sent by the client, without any rewriting or pretty printing. This
means that prepared statements created via SQL will be prefixed with
"PREPARE ... AS ", whereas those prepared via the FE/BE protocol will
not. That is unfortunate, but discussion on -patches did not yield an
efficient way to improve this, and there is some merit in returning
exactly what the client sent to the backend.

Catalog version bumped, regression tests updated.

1 files changed, 137 insertions, 5 deletions

diff --git a/src/backend/commands/prepare.c b/src/backend/commands/prepare.c
index 1ee955ebe14..ccf8c297b21 100644
--- a/src/backend/commands/prepare.c
+++ b/src/backend/commands/prepare.c
@@ -10,21 +10,26 @@
  * Copyright (c) 2002-2005, PostgreSQL Global Development Group
  *
  * IDENTIFICATION
- *	  $PostgreSQL: pgsql/src/backend/commands/prepare.c,v 1.44 2005/12/14 17:06:27 tgl Exp $
+ *	  $PostgreSQL: pgsql/src/backend/commands/prepare.c,v 1.45 2006/01/08 07:00:25 neilc Exp $
  *
  *-------------------------------------------------------------------------
  */
 #include "postgres.h"
 
+#include "access/heapam.h"
+#include "catalog/pg_type.h"
 #include "commands/explain.h"
 #include "commands/prepare.h"
 #include "executor/executor.h"
-#include "utils/guc.h"
+#include "funcapi.h"
+#include "parser/parsetree.h"
 #include "optimizer/planner.h"
 #include "rewrite/rewriteHandler.h"
 #include "tcop/pquery.h"
 #include "tcop/tcopprot.h"
 #include "tcop/utility.h"
+#include "utils/builtins.h"
+#include "utils/guc.h"
 #include "utils/hsearch.h"
 #include "utils/memutils.h"
 
@@ -40,6 +45,7 @@ static HTAB *prepared_queries = NULL;
 static void InitQueryHashTable(void);
 static ParamListInfo EvaluateParams(EState *estate,
 			   List *params, List *argtypes);
+static Datum build_oid_array(List *oid_list);
 
 /*
  * Implements the 'PREPARE' utility statement.
@@ -114,7 +120,8 @@ PrepareQuery(PrepareStmt *stmt)
 						   commandTag,
 						   query_list,
 						   plan_list,
-						   stmt->argtype_oids);
+						   stmt->argtype_oids,
+						   true);
 }
 
 /*
@@ -298,7 +305,8 @@ StorePreparedStatement(const char *stmt_name,
 					   const char *commandTag,
 					   List *query_list,
 					   List *plan_list,
-					   List *argtype_list)
+					   List *argtype_list,
+					   bool from_sql)
 {
 	PreparedStatement *entry;
 	MemoryContext oldcxt,
@@ -361,6 +369,8 @@ StorePreparedStatement(const char *stmt_name,
 	entry->plan_list = plan_list;
 	entry->argtype_list = argtype_list;
 	entry->context = entrycxt;
+	entry->prepare_time = GetCurrentTimestamp();
+	entry->from_sql = from_sql;
 
 	MemoryContextSwitchTo(oldcxt);
 }
@@ -383,7 +393,7 @@ FetchPreparedStatement(const char *stmt_name, bool throwError)
 	{
 		/*
 		 * We can't just use the statement name as supplied by the user: the
-		 * hash package is picky enough that it needs to be NULL-padded out to
+		 * hash package is picky enough that it needs to be NUL-padded out to
 		 * the appropriate length to work correctly.
 		 */
 		StrNCpy(key, stmt_name, sizeof(key));
@@ -661,3 +671,125 @@ ExplainExecuteQuery(ExplainStmt *stmt, ParamListInfo params,
 	if (estate)
 		FreeExecutorState(estate);
 }
+
+/*
+ * This set returning function reads all the prepared statements and
+ * returns a set of (name, statement, prepare_time, param_types).
+ */
+Datum
+pg_prepared_statement(PG_FUNCTION_ARGS)
+{
+	FuncCallContext	   *funcctx;
+	HASH_SEQ_STATUS    *hash_seq;
+	PreparedStatement  *prep_stmt;
+
+	/* stuff done only on the first call of the function */
+	if (SRF_IS_FIRSTCALL())
+	{
+		TupleDesc		tupdesc;
+		MemoryContext	oldcontext;
+
+		/* create a function context for cross-call persistence */
+		funcctx = SRF_FIRSTCALL_INIT();
+
+		/*
+		 * switch to memory context appropriate for multiple function
+		 * calls
+		 */
+		oldcontext = MemoryContextSwitchTo(funcctx->multi_call_memory_ctx);
+
+		/* allocate memory for user context */
+		if (prepared_queries)
+		{
+			hash_seq = (HASH_SEQ_STATUS *) palloc(sizeof(HASH_SEQ_STATUS));
+			hash_seq_init(hash_seq, prepared_queries);
+			funcctx->user_fctx = (void *) hash_seq;
+		}
+		else
+			funcctx->user_fctx = NULL;
+
+		/*
+		 * build tupdesc for result tuples. This must match the
+		 * definition of the pg_prepared_statements view in
+		 * system_views.sql
+		 */
+		tupdesc = CreateTemplateTupleDesc(5, false);
+		TupleDescInitEntry(tupdesc, (AttrNumber) 1, "name",
+						   TEXTOID, -1, 0);
+		TupleDescInitEntry(tupdesc, (AttrNumber) 2, "statement",
+						   TEXTOID, -1, 0);
+		TupleDescInitEntry(tupdesc, (AttrNumber) 3, "prepare_time",
+						   TIMESTAMPTZOID, -1, 0);
+		TupleDescInitEntry(tupdesc, (AttrNumber) 4, "parameter_types",
+						   OIDARRAYOID, -1, 0);
+		TupleDescInitEntry(tupdesc, (AttrNumber) 5, "from_sql",
+						   BOOLOID, -1, 0);
+
+		funcctx->tuple_desc = BlessTupleDesc(tupdesc);
+		MemoryContextSwitchTo(oldcontext);
+	}
+
+	/* stuff done on every call of the function */
+	funcctx = SRF_PERCALL_SETUP();
+	hash_seq = (HASH_SEQ_STATUS *) funcctx->user_fctx;
+
+	/* if the hash table is uninitialized, we're done */
+	if (hash_seq == NULL)
+		SRF_RETURN_DONE(funcctx);
+
+	prep_stmt = hash_seq_search(hash_seq);
+	if (prep_stmt)
+	{
+		Datum			result;
+		HeapTuple		tuple;
+		Datum			values[5];
+		bool			nulls[5];
+
+		MemSet(nulls, 0, sizeof(nulls));
+
+		values[0] = DirectFunctionCall1(textin,
+										CStringGetDatum(prep_stmt->stmt_name));
+
+		if (prep_stmt->query_string == NULL)
+			nulls[1] = true;
+		else
+			values[1] = DirectFunctionCall1(textin,
+									CStringGetDatum(prep_stmt->query_string));
+
+		values[2] = TimestampTzGetDatum(prep_stmt->prepare_time);
+		values[3] = build_oid_array(prep_stmt->argtype_list);
+		values[4] = BoolGetDatum(prep_stmt->from_sql);
+
+		tuple = heap_form_tuple(funcctx->tuple_desc, values, nulls);
+		result = HeapTupleGetDatum(tuple);
+		SRF_RETURN_NEXT(funcctx, result);
+	}
+
+	SRF_RETURN_DONE(funcctx);
+}
+
+/*
+ * This utility function takes a List of Oids, and returns a Datum
+ * pointing to a Postgres array containing those OIDs. The empty list
+ * is returned as a zero-element array, not NULL.
+ */
+static Datum
+build_oid_array(List *oid_list)
+{
+	ListCell *lc;
+	int len;
+	int i;
+	Datum *tmp_ary;
+	ArrayType *ary;
+
+	len = list_length(oid_list);
+	tmp_ary = (Datum *) palloc(len * sizeof(Datum));
+
+	i = 0;
+	foreach(lc, oid_list)
+		tmp_ary[i++] = ObjectIdGetDatum(lfirst_oid(lc));
+
+	/* XXX: this hardcodes assumptions about the OID type... */
+	ary = construct_array(tmp_ary, len, OIDOID, sizeof(Oid), true, 'i');
+	return PointerGetDatum(ary);
+}