[MDEV-22682] [Warning] Could not open mysql.plugin table. Some options may be missing from the help text Created: 2020-05-23  Updated: 2020-07-14  Resolved: 2020-05-28

Status: Closed
Project: MariaDB Server
Component/s: Configuration
Affects Version/s: 10.4
Fix Version/s: N/A

Type: Bug Priority: Major
Reporter: Nuno Assignee: Unassigned
Resolution: Not a Bug Votes: 0
Labels: need_feedback

Attachments: Text File bug-strace.txt    

 Description   

Upgraded to MariaDB 10.4 (from 10.3) on a new server. Used MariaBackup to restore, and then ran mysql_upgrade.

Everything loads well, MariaDB works, but I get the following warning:

[root@server ~]# mysqld --verbose --help 1>/dev/null
 
2020-05-20  0:56:22 0 [Note] Plugin 'FEEDBACK' is disabled.
 
2020-05-20  0:56:22 0 [Warning] Could not open mysql.plugin table. Some options may be missing from the help text

I'm just worried that this might cause a problem, even though it's just a warning.

By searching other people having this warning (sometimes as an 'error'), all of them said that it was solved by deleting the datadir and restarting, which is obviously not what I want...

This doesn't seem to be a permission problem, as the table is well visible (but empty):

[root@server ~]# mysql -e "show create table mysql.plugin"
 
+--------+------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+
 
| Table  | Create Table                                                                                                                                                                                                                 |
 
+--------+------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+
 
| plugin | CREATE TABLE `plugin` (
 
  `name` varchar(64) NOT NULL DEFAULT '',
 
  `dl` varchar(128) NOT NULL DEFAULT '',
 
  PRIMARY KEY (`name`)
 
) ENGINE=Aria DEFAULT CHARSET=utf8 PAGE_CHECKSUM=1 TRANSACTIONAL=1 COMMENT='MySQL plugins' |
 
+--------+------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+
 
[root@server ~]# mysql -e "select count(*) from mysql.plugin"
 
+----------+
 
| count(*) |
 
+----------+
 
|        0 |
 
+----------+
 
[root@server ~]#

How can I fix the warning? Or... is this just a false positive that can safely be ignored?

 Comments   
Comment by Sergei Golubchik [ 2020-05-27 ]

The warning only means exactly what it is saying — that your help output might be incomplete. It does not mean that anything will be wrong when you start the server.

To include plugin options into the --help output mysqld needs to read the plugin table to know what plugins you have installed. When it fails to do so, it warns you that the --help output may be incomplete.

Why it failed to read the table? May be you have another mysqld running and it prevented the first one from reading the table. May be you start your mysqld with the --datadir option and it knows how to find your tables, but just with simple --help it doesn't.

Either way, the warning in --help concerns only --help output.

Comment by Nuno [ 2020-05-28 ]

Thanks Sergei.

Well, yeah, you might be correct then, that it might be because another mysqld is running.

This "--help" command runs as part of validating our my.cnf file for syntax, while the actual Server is running for production.

This warning wasn't appearing before the 10.4 upgrade, but it could be a change made on this version.

Have a great day.

Comment by Wayne Davison (Inactive) [ 2020-07-14 ]

On docker I always get this error for 10.4 when running mysqld --verbose --help. It doesn't matter if the server is running or stopped, or if I run the command as root or mysql. I've attached some strace output that shows that the file is opened twice and read twice, and then the warning occurs, at which point the command-line options for various plugins is not included in the output.

Generated at Thu Feb 08 09:16:39 UTC 2024 using Jira 8.20.16#820016-sha1:9d11dbea5f4be3d4cc21f03a88dd11d8c8687422.