[MDEV-5829] STOP SLAVE resets global status variables Created: 2014-03-12  Updated: 2015-06-11  Resolved: 2014-03-14

Status: Closed
Project: MariaDB Server
Component/s: None
Affects Version/s: 5.5.36, 10.0.9
Fix Version/s: 5.5.37, 10.0.10

Type: Bug Priority: Critical
Reporter: Kolbe Kegel (Inactive) Assignee: Michael Widenius
Resolution: Fixed Votes: 0
Labels: None


 Description   

Using mariadb-10.0.9-linux-x86_64.tar.gz.

MariaDB [test]> show global status like 'com_insert';
 
+---------------+--------+
 
| Variable_name | Value  |
 
+---------------+--------+
 
| Com_insert    | 646298 |
 
+---------------+--------+
 
1 row in set (0.00 sec)
 
 
 
MariaDB [test]> stop slave;
 
Query OK, 0 rows affected (0.00 sec)
 
 
 
MariaDB [test]> show global status like 'com_insert';
 
+---------------+-------+
 
| Variable_name | Value |
 
+---------------+-------+
 
| Com_insert    | 0     |
 
+---------------+-------+
 
1 row in set (0.00 sec)



 Comments   
Comment by Elena Stepanova [ 2014-03-12 ]

The problem was introduced in 5.5 tree by the following revision:

revno: 3601
 
revision-id: wlad@montyprogram.com-20121220231237-0xv7egt3s225bx7j
 
parent: timour@askmonty.org-20121220203840-ofoavsm70g8ouk0m
 
committer: Vladislav Vaintroub <wlad@montyprogram.com>
 
branch nick: 5.5
 
timestamp: Fri 2012-12-21 00:12:37 +0100
 
message:
 
  MDEV-3945 - do not hold LOCK_thread_count when freeing THD.
 
    
  The patch decreases the duration of LOCK_thread_count, so it is not hold during THD destructor and freeing memory.
 
  This mutex  now only protects the integrity of threads list, when removing THD from it,  and thread_count variable.
 
    
  The add_to_status() function that updates global status during client disconnect,  is now correctly protected by the LOCK_status mutex.
 
  
  Benchmark : in a  "non-persistent" sysbench test (oltp_ro with reconnect after each query),  ~ 25% more connects/disconnects were measured

I agree that the effect is bad and must be fixed, but given that it had survived for over an year without affecting anybody heavily enough to be noticed, I demote it from Blocker

Comment by Michael Widenius [ 2014-03-14 ]

Problem was that global status was not updated when slave thread thd was deleted.

Fix pushed into 5.5. Will be in 10.0.10 when we do next merge from 5.5

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