MySQL Bugs: #71275: Manual is wrong when explaining PROCESSLIST

Bug #71275	Manual is wrong when explaining PROCESSLIST_ID for background thread
Submitted:	2 Jan 2014 14:42	Modified:	8 Jan 2014 13:17
Reporter:	Valeriy Kravchuk	Email Updates:
Status:	Closed	Impact on me:	None
Category:	MySQL Server: Documentation	Severity:	S3 (Non-critical)
Version:	5.6	OS:	Any
Assigned to:	Paul DuBois	CPU Architecture:	Any
Tags:	missing manual, performance_schema, threads

Description:
This manual page, http://dev.mysql.com/doc/refman/5.6/en/threads-table.html, says:

"PROCESSLIST_ID

For threads that are displayed in the INFORMATION_SCHEMA.PROCESSLIST table, this is the PROCESSLIST.ID value, which is also the value that CONNECTION_ID() would return within that thread. For background threads (threads not associated with a user connection), PROCESSLIST_ID is 0, so the values are not unique."

Unfortunately, PROCESSLIST_ID is NOT 0, but NULL for background threads.

How to repeat:
mysql> select thread_id, processlist_id, name from performance_schema.threads where type='BACKGROUND';
+-----------+----------------+----------------------------------------+
| thread_id | processlist_id | name                                   |
+-----------+----------------+----------------------------------------+
|         1 |           NULL | thread/sql/main                        |
|         2 |           NULL | thread/innodb/io_handler_thread        |
|         3 |           NULL | thread/innodb/io_handler_thread        |
|         4 |           NULL | thread/innodb/io_handler_thread        |
|         5 |           NULL | thread/innodb/io_handler_thread        |
|         6 |           NULL | thread/innodb/io_handler_thread        |
|         7 |           NULL | thread/innodb/io_handler_thread        |
|         8 |           NULL | thread/innodb/io_handler_thread        |
|         9 |           NULL | thread/innodb/io_handler_thread        |
|        10 |           NULL | thread/innodb/io_handler_thread        |
|        11 |           NULL | thread/innodb/io_handler_thread        |
|        14 |           NULL | thread/innodb/srv_lock_timeout_thread  |
|        15 |           NULL | thread/innodb/srv_monitor_thread       |
|        16 |           NULL | thread/innodb/srv_purge_thread         |
|        17 |           NULL | thread/innodb/srv_error_monitor_thread |
|        18 |           NULL | thread/innodb/srv_master_thread        |
|        19 |           NULL | thread/innodb/page_cleaner_thread      |
|        20 |           NULL | thread/sql/shutdown                    |
|        21 |           NULL | thread/sql/con_sockets                 |
+-----------+----------------+----------------------------------------+
19 rows in set (0.00 sec)

mysql> select thread_id, processlist_id, name from performance_schema.threads where processlist_id=0;
Empty set (0.04 sec)

Suggested fix:
Fix the manual to explain PROCESSLIST_ID properly for background threads.

Corrected synopsis.

Hello Valeriy,

Thank you for the bug report.
Verified as described.

Thanks,
Umesh

// 5.6.16
// Confirmed from the latest build..

mysql> select version();
+---------------------------------------+
| version()                             |
+---------------------------------------+
| 5.6.16-enterprise-commercial-advanced |
+---------------------------------------+
1 row in set (0.00 sec)

mysql> select thread_id, processlist_id, name from performance_schema.threads where type='BACKGROUND';
+-----------+----------------+----------------------------------------+
| thread_id | processlist_id | name                                   |
+-----------+----------------+----------------------------------------+
|         1 |           NULL | thread/sql/main                        |
|         2 |           NULL | thread/innodb/io_handler_thread        |
|         3 |           NULL | thread/innodb/io_handler_thread        |
|         4 |           NULL | thread/innodb/io_handler_thread        |
|         5 |           NULL | thread/innodb/io_handler_thread        |
|         6 |           NULL | thread/innodb/io_handler_thread        |
|         7 |           NULL | thread/innodb/io_handler_thread        |
|         8 |           NULL | thread/innodb/io_handler_thread        |
|         9 |           NULL | thread/innodb/io_handler_thread        |
|        10 |           NULL | thread/innodb/io_handler_thread        |
|        11 |           NULL | thread/innodb/io_handler_thread        |
|        13 |           NULL | thread/innodb/srv_lock_timeout_thread  |
|        14 |           NULL | thread/innodb/srv_error_monitor_thread |
|        15 |           NULL | thread/innodb/srv_monitor_thread       |
|        16 |           NULL | thread/innodb/srv_master_thread        |
|        17 |           NULL | thread/innodb/srv_purge_thread         |
|        18 |           NULL | thread/innodb/page_cleaner_thread      |
|        19 |           NULL | thread/sql/signal_handler              |
+-----------+----------------+----------------------------------------+
18 rows in set (0.00 sec)

mysql> select thread_id, processlist_id, name from performance_schema.threads where processlist_id=0;
Empty set (0.00 sec)

mysql>

You are correct. I asked Marc about this and it changed in MySQL 5.6.9.

Thank you for your bug report. This issue has been addressed in the documentation. The updated documentation will appear on our website shortly, and will be included in the next release of the relevant products.