[#26191] YSQL: Disable fast-path transaction for bulk load on colocat…

…ed table by default

Summary:
Add a flag FLAGS_ysql_colocated_fastpath_txn_copy to enable/disable the fast-path transaction
for bulk load on colocated table. Disable it by default.
Jira: DB-15536

Test Plan: manual test.

Reviewers: pjain, rthallam

Reviewed By: pjain

Subscribers: yql

Differential Revision: https://phorge.dev.yugabyte.com/D42163

src/postgres/src/backend/commands/copyfrom.c

@@ -751,7 +751,8 @@ CopyFrom(CopyFromState cstate)
 	 */
 	bool has_rule_or_trigger = resultRelInfo->ri_RelationDesc->rd_rel->relhastriggers ||
 		resultRelInfo->ri_RelationDesc->rd_rel->relhasrules;
-	if (!set_txn_batch_size_explicitly && IsYBRelation(resultRelInfo->ri_RelationDesc) &&
+	if (yb_fast_path_for_colocated_copy &&
+		!set_txn_batch_size_explicitly && IsYBRelation(resultRelInfo->ri_RelationDesc) &&
 		YbGetTableProperties(resultRelInfo->ri_RelationDesc)->is_colocated &&
 		!has_rule_or_trigger && !IsTransactionBlock())
 	{

src/postgres/src/backend/executor/ybModifyTable.c

@@ -74,6 +74,7 @@
 
 bool		yb_disable_transactional_writes = false;
 bool		yb_enable_upsert_mode = false;
+bool		yb_fast_path_for_colocated_copy = false;
 
 /*
  * Hack to ensure that the next CommandCounterIncrement() will call

src/postgres/src/backend/utils/misc/guc.c

@@ -2758,6 +2758,17 @@ static struct config_bool ConfigureNamesBool[] =
 		false,
 		NULL, NULL, NULL
 	},
+
+	{
+		{"yb_fast_path_for_colocated_copy", PGC_USERSET, CLIENT_CONN_STATEMENT,
+			gettext_noop("Enable fast-path transaction for copy on colocated tables. For testint now."),
+			NULL
+		},
+		&yb_fast_path_for_colocated_copy,
+		false,
+		NULL, NULL, NULL
+	},
+
 	{
 		{"suppress_nonpg_logs", PGC_SIGHUP, LOGGING_WHAT,
 			gettext_noop("Suppresses non-Postgres logs from appearing in the Postgres log file."),

src/postgres/src/include/executor/ybModifyTable.h

@@ -32,6 +32,14 @@
  */
 extern bool yb_disable_transactional_writes;
 
+/**
+ * YSQL guc variables that can be used to enable/disable fast-path transaction
+ * on colocated tables for copy.
+ * e.g. 'SET yb_fast_path_for_colocated_copy=true'
+ * See also the corresponding entries in guc.c.
+ */
+extern bool yb_fast_path_for_colocated_copy;
+
 /**
  * YSQL guc variables that can be used to enable upsert mode for writes.
  * e.g. 'SET yb_enable_upsert_mode=true'

src/yb/yql/pgwrapper/pg_op_buffering-test.cc

@@ -383,6 +383,7 @@ void TestBulkLoadUseFastPathForColocated(PGConn* conn, const std::string& table_
   generateCSVFileForCopy(csv_filename, num_rows, num_indices + 2);
   const int total_write_entries = num_rows * (num_indices + 1);
   ASSERT_OK(CreateTableWithIndex(conn, table_name, num_indices));
+  ASSERT_OK(conn->Execute("SET yb_fast_path_for_colocated_copy=true"));
   // will take 2 buffers if not adjusted
   ASSERT_OK(SetMaxBatchSize(conn, total_write_entries - 1));
   auto write_rpc_count = ASSERT_RESULT(write_rpc_watcher->Delta(