MySQL Master Long Running `set @slave_uuid = ?`

Question

My MySQL master DB is replicating to my slave just fine, but I have a long running query that does not go away after a reboot:  
  
`set @slave_uuid = ?`  
  
My `show processlist` doesn't have anything suspicious or long running, so I don't know where this is coming from.  
  
Curiously, my `show slave status` query returns an empty list. Not sure why it wouldn't show the slave that's configured already.  
  
Anyone have any ideas or areas I could poke on to help figure this out? I'm puzzled.  
  
Thanks!

Answer

Greetings,  
  
This may be related to a bug in MySQL Performance Schema \[1] if you are using any of the following MySQL versions:  
=>5.6.46  
=>5.7.28  
=>8.0.18  
  
It's not really a long running query, just a misrepresentation on the PI dashboard as the query is not actually executing or consuming any resources. Since, Performance Insights is capturing thread information from "performance_schema.threads", the PI console displays this query "SET @slave_uuid= ?" as being executed and consuming resources on the instance.   
It doesn't really affect instance performance and is safe to be ignored. If you wish to remove it, take logical dump of the database and restore it to an RDS MySQL version not mentioned in the above list.   
  
\[1] PSI thread info not getting updated after statement execution - https://bugs.mysql.com/bug.php?id=99039  
  
Hope this helps!  
  
- Dhanraj  
  
Edited by: DhanrajAtAWS on Oct 23, 2020 10:47 AM

Answer

Probably related and what I'm currently investigating, the top wait is:  
  
wait/synch/cond/sql/MYSQL_BIN_LOG::update_cond  
  
Again, all related to master/slave, but still not sure what's causing this or how to clear it.

MySQL Master Long Running `set @slave_uuid = ?`

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