| Bug #97358 | The log.flush_notifier_mutex in log_sys is useless | ||
|---|---|---|---|
| Submitted: | 24 Oct 2019 11:59 | Modified: | 25 Oct 2019 11:53 |
| Reporter: | Zongzhi Chen (OCA) | Email Updates: | |
| Status: | Verified | Impact on me: | |
| Category: | MySQL Server: InnoDB storage engine | Severity: | S5 (Performance) |
| Version: | 8.0.* | OS: | Any |
| Assigned to: | CPU Architecture: | Any | |
[24 Oct 2019 12:36]
MySQL Verification Team
Hello Mr. zongzhi, Thank you for your bug report. What you write is true, but there is one detail that you miss. That code, which you are referring to, can run in several threads. Hence, the mutex lock is necessary. Let us know if you disagree ........
[24 Oct 2019 19:06]
Zongzhi Chen
No, I am not agree.
There is only one log_flush_notifier..
The log_flush_notifier thread is created in log_start_background_threads() function
```
srv_threads.m_log_flush_notifier =
os_thread_create(log_flush_notifier_thread_key, log_flush_notifier, &log);
```
[25 Oct 2019 11:53]
MySQL Verification Team
Hi Mr. zongzhi, I have revisited the code and I think that you are right. Verified as a performance improvement contribution.
Description: Hello The MySQL code version is 8.0.17 There is only three places that call log_flush_notifier_mutex_enter(log), all of these places ad in log_flush_notifier function(). And there is only one log_flush_notifier thread that will call this function. The log_flush_notifier thread is used for notifier user thread if the redo log that it write has flush to disk The whole there place is below: ``` 2397 void log_flush_notifier(log_t *log_ptr) { 2398 ut_a(log_ptr != nullptr); 2399 2400 log_t &log = *log_ptr; 2401 lsn_t lsn = log.flushed_to_disk_lsn.load() + 1; 2402 2403 log_flush_notifier_mutex_enter(log); 2404 2405 Log_thread_waiting waiting{log, log.flush_notifier_event, 2406 srv_log_flush_notifier_spin_delay, 2407 srv_log_flush_notifier_timeout}; 2408 ........ 2422 2423 auto stop_condition = [&log, lsn, &released](bool wait) { 2424 LOG_SYNC_POINT("log_flush_notifier_after_event_reset"); 2425 if (released) { 2426 log_flush_notifier_mutex_enter(log); 2427 released = false; 2428 } 2429 2430 LOG_SYNC_POINT("log_flush_notifier_before_check"); 2431 ... 2441 2442 if (wait) { 2443 log_flush_notifier_mutex_exit(log); 2444 released = true; 2445 } 2446 LOG_SYNC_POINT("log_flush_notifier_before_wait"); 2447 2448 return (false); 2449 }; ``` How to repeat: read the code