Bug #79809 "ROW OPERATIONS" print by `SHOW ENGINE INNODB STATUS` is not correct
Submitted: 30 Dec 2015 8:09 Modified: 30 Dec 2015 18:22
Reporter: zhai weixiang (OCA) Email Updates:
Status: Verified Impact on me:
Category:MySQL Server: InnoDB storage engine Severity:S3 (Non-critical)
Version:5.7 5.6 OS:Any
Assigned to: CPU Architecture:Any

[30 Dec 2015 8:09] zhai weixiang
While executing `show engine innodb status`, it will calculate the average DML rates per second.  But if I execute `show engine innodb status` twice in less than one second. It will print wrong number like this:
8 queries inside InnoDB, 0 queries in queue
8 read views open inside InnoDB
Process ID=52440, Main thread ID=46949392733952, state: sleeping
Number of rows inserted 1527921, updated 3025374, deleted 1512681, read 615480446
2380000.00 inserts/s, 4765000.00 updates/s, 2383000.00 deletes/s, 968512000.00 reads/s

Check the code:
                "%.2f inserts/s, %.2f updates/s,"
                " %.2f deletes/s, %.2f reads/s\n",
                ((ulint) srv_stats.n_rows_inserted - srv_n_rows_inserted_old)
                / time_elapsed,
                ((ulint) srv_stats.n_rows_updated - srv_n_rows_updated_old)
                / time_elapsed,
                ((ulint) srv_stats.n_rows_deleted - srv_n_rows_deleted_old)
                / time_elapsed,
                ((ulint) srv_stats.n_rows_read - srv_n_rows_read_old)
                / time_elapsed);

Here time_elapsed is calculated by current time minus srv_last_monitor_time and add 0.001.  And if I execute the command in less than one second, time_elapsed equals to 0.001.

How to repeat:
Described above

Suggested fix:
Use a higher precision unit (for example, millisecond) to calculate the time interval.
[30 Dec 2015 18:22] MySQL Verification Team
I could verify this without checking as it's plagued us for years...
A quick test proves it..

Number of rows inserted 45374, updated 9595, deleted 45288, read 144428
1972.03 inserts/s, 378.62 updates/s, 1973.03 deletes/s, 6437.56 reads/s
Number of rows inserted 47087, updated 10082, deleted 46997, read 150446
1711.29 inserts/s, 486.51 updates/s, 1707.29 deletes/s, 6011.99 reads/s
Number of rows inserted 48548, updated 10343, deleted 48460, read 155317
1461000.00 inserts/s, 261000.00 updates/s, 1463000.00 deletes/s, 4871000.00 reads/s
[30 Dec 2015 18:38] MySQL Verification Team
people have to ignore the per/second values when top of innodb status says 
"Per second averages calculated from the last 0 seconds".

fwiw, tools can rather use information_schema.innodb_metrics to get the data far easier.