MDEV-6605 Multiple Clients Inserting Causing Error: Failed to read auto-increment value from storage engine

* handler::get_auto_increment() was not expecting any errors from the storage engine.
  That was wrong, errors could happen.
* ha_partition::get_auto_increment() was doing index lookups in partition under a mutex.
  This was redundant (engine transaction isolation was covering that anyway)
  and harmful (causing deadlocks).

sql/ha_partition.cc

@@ -7854,8 +7854,7 @@ void ha_partition::get_auto_increment(ulonglong offset, ulonglong increment,
     ulonglong first_value_part, max_first_value;
     handler **file= m_file;
     first_value_part= max_first_value= *first_value;
-    /* Must lock and find highest value among all partitions. */
-    lock_auto_increment();
+    /* Must find highest value among all partitions. */
     do
     {
       /* Only nb_desired_values = 1 makes sense */
@@ -7866,7 +7865,6 @@ void ha_partition::get_auto_increment(ulonglong offset, ulonglong increment,
         *first_value= first_value_part;
         /* log that the error was between table/partition handler */
         sql_print_error("Partition failed to reserve auto_increment value");
-        unlock_auto_increment();
         DBUG_VOID_RETURN;
       }
       DBUG_PRINT("info", ("first_value_part: %lu", (ulong) first_value_part));
@@ -7874,7 +7872,6 @@ void ha_partition::get_auto_increment(ulonglong offset, ulonglong increment,
     } while (*(++file));
     *first_value= max_first_value;
     *nb_reserved_values= 1;
-    unlock_auto_increment();
   }
   else
   {

sql/handler.cc

@@ -2819,15 +2819,10 @@ void handler::get_auto_increment(ulonglong offset, ulonglong increment,
   if (error)
   {
     if (error == HA_ERR_END_OF_FILE || error == HA_ERR_KEY_NOT_FOUND)
-    {
-      /* No entry found, start with 1. */
-      nr= 1;
-    }
+      /* No entry found, that's fine */;
     else
-    {
-      DBUG_ASSERT(0);
-      nr= ULONGLONG_MAX;
-    }
+      print_error(error, MYF(0));
+    nr= 1;
   }
   else
     nr= ((ulonglong) table->next_number_field->

storage/tokudb/mysql-test/tokudb_mariadb/r/autoinc.result

@@ -0,0 +1,36 @@
+create table t1 (a int auto_increment, b bigint(20), primary key (b,a)) engine=tokudb;
+start transaction;
+insert t1 (b) values (1);
+set tokudb_lock_timeout=1;
+insert t1 (b) values (1);
+ERROR HY000: Lock wait timeout exceeded; try restarting transaction
+set tokudb_lock_timeout=default;
+insert t1 (b) values (1);
+insert t1 (b) values (1);
+commit;
+commit;
+select * from t1;
+a	b
+1	1
+2	1
+3	1
+alter table t1 partition by range (b) (partition p0 values less than (9));
+start transaction;
+insert t1 (b) values (2);
+set tokudb_lock_timeout=1;
+insert t1 (b) values (2);
+ERROR HY000: Lock wait timeout exceeded; try restarting transaction
+set tokudb_lock_timeout=default;
+insert t1 (b) values (2);
+insert t1 (b) values (2);
+commit;
+commit;
+select * from t1;
+a	b
+1	1
+2	1
+3	1
+1	2
+2	2
+3	2
+drop table t1;

storage/tokudb/mysql-test/tokudb_mariadb/t/autoinc.test

@@ -0,0 +1,51 @@
+#
+# MDEV-6605 Multiple Clients Inserting Causing Error: Failed to read auto-increment value from storage engine
+#
+
+--source include/have_partition.inc
+create table t1 (a int auto_increment, b bigint(20), primary key (b,a)) engine=tokudb;
+
+# first, without partitions
+start transaction;
+insert t1 (b) values (1);
+
+--connect(con2,localhost,root)
+set tokudb_lock_timeout=1;
+# auto-inc value is locked
+--error ER_LOCK_WAIT_TIMEOUT
+insert t1 (b) values (1);
+# but no deadlock
+set tokudb_lock_timeout=default;
+--send insert t1 (b) values (1)
+--connection default
+insert t1 (b) values (1);
+commit;
+--connection con2
+--reap
+commit;
+select * from t1;
+
+# now with partitions
+--connection default
+alter table t1 partition by range (b) (partition p0 values less than (9));
+start transaction;
+insert t1 (b) values (2);
+
+--connection con2
+set tokudb_lock_timeout=1;
+# auto-inc value is locked
+--error ER_LOCK_WAIT_TIMEOUT
+insert t1 (b) values (2);
+# but no deadlock
+set tokudb_lock_timeout=default;
+--send insert t1 (b) values (2)
+--connection default
+insert t1 (b) values (2);
+commit;
+--connection con2
+--reap
+commit;
+select * from t1;
+
+drop table t1;
+