Subject Re: High "Mutex wait" value, after increase in "Hash Slots" to 90001
Author Dmitry Yemanov
10.03.2017 23:58, 'Leyne, Sean' wrote:
> We have a client with 320GB database (running FB CS v2.5)

Is it really so? FB does not support LockHashSlots more than 64K, it
would truncate your 90001 down to 65521.

> Yesterday, I ran fb_lock_print to check on the database and found a
> “Mutex wait” value of 20.9%, which I knew that a “bad thing”. So, I
> increased (by 50%) the “Hash slots” value from 60011 to 90001.

These value are not directly related. Most probably, you didn't need to
change that setting.

> Now, today, I checked the lock print values again, and got even worse
> numbers!!!

The change didn't help, the reason is elsewhere. 21% vs 23% could be
explained by e.g. printing the stats at 3PM and 5PM. And we don't know
what was the mutex wait ratio before they reported the performance issues.

> Hash slots: 90001, Hash lengths (min/avg/max): 0/
> 0/ 5

Hash stats looks good.

> Owners (288): forward: 732776, backward: 29775680
> Free owners (400): forward: 9817904, backward: 9548560

688 peak connections. Is this expected? Could the load be growing recently?

> Any suggestions on how I can improve the numbers?

Nothing based on this lock print.