From ca48cb81c4191e5ce94bbc57af96323045ac2c82 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Ren=C3=A9=20Canna=C3=B2?= <rene.cannao@gmail.com>
Date: Tue, 13 Nov 2018 17:34:03 +0200
Subject: [PATCH] Revert autcommit to 1 if it is the first SELECT

If:
* client wants autocommit=0
* enforce_autocommit_on_reads=false
* there is no transaction
* this seems to be the first query, and a SELECT not FOR UPDATE
Action:
* switch back to autcommit=1
---
 lib/MySQL_Session.cpp | 35 ++++++++++++++++++++++++++++++++++-
 1 file changed, 34 insertions(+), 1 deletion(-)

diff --git a/lib/MySQL_Session.cpp b/lib/MySQL_Session.cpp
index 86d0ec64a..4e10873b2 100644
--- a/lib/MySQL_Session.cpp
+++ b/lib/MySQL_Session.cpp
@@ -1343,6 +1343,24 @@ bool MySQL_Session::handler_again___verify_backend_autocommit() {
 			}
 			NEXT_IMMEDIATE_NEW(CHANGING_AUTOCOMMIT);
 		}
+	} else {
+		if (autocommit == false) { // also IsAutoCommit==false
+			if (mysql_thread___enforce_autocommit_on_reads == false) {
+				if (mybe->server_myds->myconn->IsActiveTransaction() == false) {
+					if (CurrentQuery.is_select_NOT_for_update()==true) {
+						// client wants autocommit=0
+						// enforce_autocommit_on_reads=false
+						// there is no transaction
+						// this seems to be the first query, and a SELECT not FOR UPDATE
+						// we will switch back to autcommit=1
+						if (status == PROCESSING_QUERY) {
+							previous_status.push(PROCESSING_QUERY);
+							NEXT_IMMEDIATE_NEW(CHANGING_AUTOCOMMIT);
+						}
+					}
+				}
+			}
+		}
 	}
 	return false;
 }
@@ -2019,7 +2037,22 @@ bool MySQL_Session::handler_again___status_CHANGING_AUTOCOMMIT(int *_rc) {
 	if (myds->mypolls==NULL) {
 		thread->mypolls.add(POLLIN|POLLOUT, mybe->server_myds->fd, mybe->server_myds, thread->curtime);
 	}
-	int rc=myconn->async_set_autocommit(myds->revents, autocommit);
+	bool ac = autocommit;
+	if (autocommit == false) { // also IsAutoCommit==false
+		if (mysql_thread___enforce_autocommit_on_reads == false) {
+			if (mybe->server_myds->myconn->IsActiveTransaction() == false) {
+				if (CurrentQuery.is_select_NOT_for_update()==true) {
+					// client wants autocommit=0
+					// enforce_autocommit_on_reads=false
+					// there is no transaction
+					// this seems to be the first query, and a SELECT not FOR UPDATE
+					// we will switch back to autcommit=1
+					ac = true;
+				}
+			}
+		}
+	}
+	int rc=myconn->async_set_autocommit(myds->revents, ac);
 	if (rc==0) {
 		st=previous_status.top();
 		previous_status.pop();