[#21757] YSQL: Support for single-use GUC variables in YSQL Connectio…

…n Manager

Summary:
YSQL Connection Manager stores the context of altered GUC variables for each logical connection, and replays the stored context at the beginning of every transaction boundary on the physical connection being used. There are some variables that are implicitly set to a different value after a certain event has occurred.
One such example of this is `yb_test_fail_next_ddl`, which returns an error upon the execution of the next DDL statement, and then sets itself to false. These implicit changes cannot be tracked by Connection Manager, and this patch creates the provision for Connection Manager to do so.

Changes in this diff:
- Remove changes made as a "hack" to pass a test in TestYsqlUpgrade.java
- When connection manager is the client, if any of the variables in the single-use category are implicitly changed, send a ParameterStatus packet back to Connection Manager

Jira: DB-10631

Test Plan:
Jenkins: enable connection manager, test regex: .*TestYsqlUpgrade.*

./yb_build.sh --enable-ysql-conn-mgr-test --java-test org.yb.pgsql.TestYsqlUpgrade#creatingSystemRelsAfterFailure

Reviewers: nkumar, mkumar

Reviewed By: nkumar

Subscribers: yql

Differential Revision: https://phorge.dev.yugabyte.com/D34450

java/yb-pgsql/src/test/java/org/yb/pgsql/TestYsqlUpgrade.java

@@ -450,9 +450,6 @@ public void creatingSystemRelsAfterFailure() throws Exception {
 
       // Letting CatalogManagerBgTasks do the cleanup.
       Thread.sleep(BuildTypeUtil.adjustTimeout(5000));
-      if (isTestRunningWithConnectionManager()) {
-        stmt.execute("SET yb_test_fail_next_ddl TO false");
-      }
       stmt.execute(ddlSql);
 
       String selectSql = "SELECT * FROM simple_system_table";

src/postgres/src/backend/catalog/yb_catalog/yb_catalog_version.c

@@ -316,6 +316,9 @@ bool YbIncrementMasterCatalogVersionTableEntry(bool is_breaking_change,
 	if (yb_test_fail_next_inc_catalog_version)
 	{
 		yb_test_fail_next_inc_catalog_version = false;
+		if (YbIsClientYsqlConnMgr())
+			YbSendParameterStatusForConnectionManager("yb_test_fail_next_inc_catalog_version",
+				"false");
 		elog(ERROR, "Failed increment catalog version as requested");
 	}
 

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

@@ -1441,7 +1441,12 @@ YBResetEnableNonBreakingDDLMode()
 	/*
 	 * Reset yb_make_next_ddl_statement_nonbreaking to avoid its further side
 	 * effect that may not be intended.
+	 * 
+	 * Also, reset Connection Manager cache if the value was cached to begin
+	 * with.
 	 */
+	if (YbIsClientYsqlConnMgr() && yb_make_next_ddl_statement_nonbreaking)
+		YbSendParameterStatusForConnectionManager("yb_make_next_ddl_statement_nonbreaking", "false");
 	yb_make_next_ddl_statement_nonbreaking = false;
 }
 
@@ -1544,6 +1549,8 @@ YBDecrementDdlNestingLevel()
 	if (yb_test_fail_next_ddl)
 	{
 		yb_test_fail_next_ddl = false;
+		if (YbIsClientYsqlConnMgr())
+			YbSendParameterStatusForConnectionManager("yb_test_fail_next_ddl", "false");
 		elog(ERROR, "Failed DDL operation as requested");
 	}
 	if (ddl_transaction_state.nesting_level == 0)

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

@@ -862,3 +862,27 @@ YbGetNumYsqlConnMgrConnections(const char *db_name, const char *user_name,
 	shmdt(shmp);
 	return true;
 }
+
+/* 
+ * Create a provision to send a ParameterStatus packet back to Connection Manager to
+ * change the cached value of a certain GUC variable, outside of the usual
+ * ReportGucOption function. This can be useful for some implicit changes to
+ * GUC variable values that do not normally send a ParameterStatus packet
+ * back to Connection Manager.
+ */
+void
+YbSendParameterStatusForConnectionManager(const char *name, const char *value)
+{
+	Assert(YbIsClientYsqlConnMgr());
+
+	CHECK_FOR_INTERRUPTS();
+	StringInfoData msgbuf;
+
+	pq_beginmessage(&msgbuf, 'S');
+	pq_sendstring(&msgbuf, name);
+	pq_sendstring(&msgbuf, value);
+	pq_endmessage(&msgbuf);
+
+	pq_flush();
+	CHECK_FOR_INTERRUPTS();
+}

src/postgres/src/include/yb_ysql_conn_mgr_helper.h

@@ -94,3 +94,5 @@ extern bool YbGetNumYsqlConnMgrConnections(const char *db_name,
 										   uint32_t *num_physical_conn);
 
 extern void yb_is_client_ysqlconnmgr_assign_hook(bool newval, void *extra);
+
+extern void YbSendParameterStatusForConnectionManager(const char *name, const char *value);