Add backward compatibility option that disables joins transformation (#7910)

Author: dyemanov

src/common/config/config.h

@@ -192,6 +192,7 @@ enum ConfigKey
 	KEY_PARALLEL_WORKERS,
 	KEY_MAX_PARALLEL_WORKERS,
 	KEY_OPTIMIZE_FOR_FIRST_ROWS,
+	KEY_OUTER_JOIN_CONVERSION,
 	MAX_CONFIG_KEY		// keep it last
 };
 
@@ -310,7 +311,8 @@ constexpr ConfigEntry entries[MAX_CONFIG_KEY] =
 	{TYPE_INTEGER,	"MaxStatementCacheSize",	false,	2 * 1048576},	// bytes
 	{TYPE_INTEGER,	"ParallelWorkers",			true,	1},
 	{TYPE_INTEGER,	"MaxParallelWorkers",		true,	1},
-	{TYPE_BOOLEAN,	"OptimizeForFirstRows",		false,	false}
+	{TYPE_BOOLEAN,	"OptimizeForFirstRows",		false,	false},
+	{TYPE_BOOLEAN,	"OuterJoinConversion",		false,	true}
 };
 
 
@@ -638,6 +640,8 @@ class Config : public RefCounted, public GlobalStorage
 	CONFIG_GET_GLOBAL_INT(getMaxParallelWorkers, KEY_MAX_PARALLEL_WORKERS);
 
 	CONFIG_GET_PER_DB_BOOL(getOptimizeForFirstRows, KEY_OPTIMIZE_FOR_FIRST_ROWS);
+
+	CONFIG_GET_PER_DB_BOOL(getOuterJoinConversion, KEY_OUTER_JOIN_CONVERSION);
 };
 
 // Implementation of interface to access master configuration file

src/jrd/RecordSourceNodes.cpp

@@ -2888,7 +2888,9 @@ RseNode* RseNode::pass1(thread_db* tdbb, CompilerScratch* csb)
 void RseNode::pass1Source(thread_db* tdbb, CompilerScratch* csb, RseNode* rse,
 	BoolExprNode** boolean, RecordSourceNodeStack& stack)
 {
-	if (rse_jointype != blr_inner)
+	const auto dbb = tdbb->getDatabase();
+
+	if (rse_jointype != blr_inner && dbb->dbb_config->getOuterJoinConversion())
 	{
 		// Check whether any of the upper level booleans (those belonging to the WHERE clause)
 		// is able to filter out rows from the "inner" streams. If this is the case,