If the slow query log is enabled and FILE  is selected as an output destination, each statement written to the log is preceded by a line that begins with a #  character and has these fields (with all fields on a single line): 

• Query_time: duration 

The statement execution time in seconds. 

• Lock_time: duration 

The time to acquire locks in seconds. 

• Rows_sent: N 

The number of rows sent to the client. 

• Rows_examined: 

The number of rows examined by the server layer (not counting any processing internal to storage engines). 

Enabling the log_slow_extra  system variable (available as of MySQL 8.0.14) causes the server to write the following extra fields to FILE  output in addition to those just listed ( TABLE  output is unaffected). Some field descriptions refer to status variable names. Consult the status variable descriptions for more information. However, in the slow query log, the counters are per-statement values, not cumulative per- session values. 

• Thread_id: ID 

The statement thread identifier. 

• Errno: error_number 

The statement error number, or 0 if no error occurred. 

• Killed: N 

If the statement was terminated, the error number indicating why, or 0 if the statement terminated normally. 

• Bytes_received: N 

The Bytes_received  value for the statement. 

• Bytes_sent: N 

The Bytes_sent  value for the statement. 

• Read_first: N 

The Handler_read_first  value for the statement. 

• Read_last: N 

The Handler_read_last  value for the statement. 

• Read_key: N 

The Handler_read_key  value for the statement. 

