Report deadlocks to the error log if log_warnings>2

To trace down the cause of a deadlock, ensure that for every
instance of reporting ER_LOCK_DEADLOCK, a message will be output
to the server error log if the log_warnings level is more than 2.

To enable the output: SET GLOBAL log_warnings=3;

8 files changed, 25 insertions, 3 deletions

diff --git a/sql/handler.cc b/sql/handler.cc
index 79ccf272a1a..e2ad605bf77 100644
--- a/sql/handler.cc
+++ b/sql/handler.cc
@@ -3669,6 +3669,7 @@ void handler::print_error(int error, myf errflag)
     get_error_message(error, &str);
     full_err_msg.append(str);
     my_printf_error(ER_LOCK_DEADLOCK, "%s", errflag, full_err_msg.c_ptr_safe());
+    if (global_system_variables.log_warnings > 2) errflag|= MYF(ME_ERROR_LOG);
     DBUG_VOID_RETURN;
   }
   case HA_ERR_READ_ONLY_TRANSACTION:
diff --git a/sql/mdl.cc b/sql/mdl.cc
index ce2e29bc66f..671943299ef 100644
--- a/sql/mdl.cc
+++ b/sql/mdl.cc
@@ -2172,6 +2172,8 @@ MDL_context::acquire_lock(MDL_request *mdl_request, double lock_wait_timeout)
     {
     case MDL_wait::VICTIM:
       my_error(ER_LOCK_DEADLOCK, MYF(0));
+      if (global_system_variables.log_warnings > 2)
+        sql_print_information("MDL deadlock victim killed");
       break;
     case MDL_wait::TIMEOUT:
       my_error(ER_LOCK_WAIT_TIMEOUT, MYF(0));
diff --git a/sql/rpl_parallel.cc b/sql/rpl_parallel.cc
index 34f9113f7fe..9f279433bc1 100644
--- a/sql/rpl_parallel.cc
+++ b/sql/rpl_parallel.cc
@@ -629,6 +629,8 @@ convert_kill_to_deadlock_error(rpl_group_info *rgi)
   {
     thd->clear_error();
     my_error(ER_LOCK_DEADLOCK, MYF(0));
+    if (global_system_variables.log_warnings > 2)
+      sql_print_information("convert_kill_to_deadlock_error");
     thd->reset_killed();
   }
 }
diff --git a/sql/sql_base.cc b/sql/sql_base.cc
index 986064129d6..70c1f11ffd4 100644
--- a/sql/sql_base.cc
+++ b/sql/sql_base.cc
@@ -2401,8 +2401,11 @@ Locked_tables_list::reopen_tables(THD *thd)
                          mysql_lock_merge(thd->lock, lock)) == NULL)
     {
       unlink_all_closed_tables(thd, lock, reopen_count);
-      if (! thd->killed)
+      if (! thd->killed) {
         my_error(ER_LOCK_DEADLOCK, MYF(0));
+        if (global_system_variables.log_warnings > 2)
+          sql_print_information("deadlock in Locked_tables_list");
+      }
       DBUG_RETURN(TRUE);
     }
     thd->lock= merged_lock;
@@ -2825,6 +2828,8 @@ request_backoff_action(enum_open_table_action action_arg,
   if (action_arg == OT_BACKOFF_AND_RETRY && m_has_locks)
   {
     my_error(ER_LOCK_DEADLOCK, MYF(0));
+    if (global_system_variables.log_warnings > 2)
+      sql_print_information("deadlock in request_backoff_action");
     m_thd->mark_transaction_to_rollback(true);
     return TRUE;
   }
diff --git a/sql/sql_parse.cc b/sql/sql_parse.cc
index 09bb628ea8b..060d1e2005d 100644
--- a/sql/sql_parse.cc
+++ b/sql/sql_parse.cc
@@ -7841,7 +7841,8 @@ static void wsrep_mysql_parse(THD *thd, char *rawbuf, uint length,
                       thd->wsrep_retry_counter, 
                       thd->variables.wsrep_retry_autocommit, thd->query());
           my_message(ER_LOCK_DEADLOCK, "Deadlock: wsrep aborted transaction",
-                     MYF(0));
+                     global_system_variables.log_warnings > 2
+                     ? MYF(ME_ERROR_LOG) : MYF(0));
           thd->reset_killed();
           thd->wsrep_conflict_state= NO_CONFLICT;
           if (thd->wsrep_conflict_state != REPLAYING)
diff --git a/sql/table.cc b/sql/table.cc
index ce6c7d4ddb8..72e9707ea6d 100644
--- a/sql/table.cc
+++ b/sql/table.cc
@@ -4459,6 +4459,8 @@ bool TABLE_SHARE::wait_for_old_version(THD *thd, struct timespec *abstime,
     return FALSE;
   case MDL_wait::VICTIM:
     my_error(ER_LOCK_DEADLOCK, MYF(0));
+    if (global_system_variables.log_warnings > 2)
+      sql_print_information("deadlock in wait_for_old_version");
     return TRUE;
   case MDL_wait::TIMEOUT:
     my_error(ER_LOCK_WAIT_TIMEOUT, MYF(0));
diff --git a/sql/transaction.cc b/sql/transaction.cc
index a6db204c45b..d89b4d5c18b 100644
--- a/sql/transaction.cc
+++ b/sql/transaction.cc
@@ -106,7 +106,8 @@ static bool xa_trans_rolled_back(XID_STATE *xid_state)
       my_error(ER_XA_RBTIMEOUT, MYF(0));
       break;
     case ER_LOCK_DEADLOCK:
-      my_error(ER_XA_RBDEADLOCK, MYF(0));
+      my_error(ER_XA_RBDEADLOCK, global_system_variables.log_warnings > 2
+               ? MYF(ME_ERROR_LOG) : MYF(0));
       break;
     default:
       my_error(ER_XA_RBROLLBACK, MYF(0));
diff --git a/storage/innobase/handler/ha_innodb.cc b/storage/innobase/handler/ha_innodb.cc
index 0e5af0b1f6a..ece8dda6fb5 100644
--- a/storage/innobase/handler/ha_innodb.cc
+++ b/storage/innobase/handler/ha_innodb.cc
@@ -2023,6 +2023,14 @@ convert_error_code_to_mysql(
 
 		if (thd != NULL) {
 			thd_mark_transaction_to_rollback(thd, 1);
+			if (global_system_variables.log_warnings > 2) {
+				size_t len;
+				const char* q = innobase_get_stmt_unsafe(
+					thd, &len);
+				sql_print_information(
+					"InnoDB deadlock for %s",
+					q ? q : "(unknown)");
+			}
 		}
 
 		return(HA_ERR_LOCK_DEADLOCK);