[MDEV-25425] Useless message "If the mysqld execution user is authorized page cleaner thread priority can be changed." Created: 2021-04-15  Updated: 2021-04-15  Resolved: 2021-04-15

Status: Closed
Project: MariaDB Server
Component/s: Storage Engine - InnoDB
Affects Version/s: 10.2, 10.3, 10.4, 10.5, 10.6
Fix Version/s: 10.5.10, 10.6.0

Type: Bug Priority: Major
Reporter: Marko Mäkelä Assignee: Marko Mäkelä
Resolution: Fixed Votes: 0
Labels: performance

Issue Links:
Relates
relates to MDEV-23855 InnoDB log checkpointing causes regre... Closed

 Description   

On startup, InnoDB tries to prioritize the page cleaner thread. This usually fails, resulting in a log message like the following:

Apr 15 03:28:17 ubuntu-focal-amd64 mariadbd[4875]: 2021-04-15  3:28:17 0 [Note] InnoDB: If the mysqld execution user is authorized, page cleaner thread priority can be changed. See the man page of setpriority().

A search for that message in this bug reporting system reveals many community user bugs. So, it seems that this code is almost never effective and can be removed:

#ifdef UNIV_LINUX
 
  /* linux might be able to set different setting for each thread.
 
  worth to try to set high priority for the page cleaner thread */
 
  const pid_t tid= static_cast<pid_t>(syscall(SYS_gettid));
 
  setpriority(PRIO_PROCESS, tid, -20);
 
  if (getpriority(PRIO_PROCESS, tid) != -20)
 
    ib::info() << "If the mysqld execution user is authorized,"
 
                  " page cleaner thread priority can be changed."
 
                  " See the man page of setpriority().";
 
#endif /* UNIV_LINUX */

When this code was heavily refactored in MDEV-23855, the throughput and latency were greatly improved even when the buf_flush_page_cleaner thread always ran the same priority with other threads in our benchmarks.

So, this code should have no benefit in MariaDB Server 10.5.7 or later.
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