The top filter is a filter module for MariaDB MaxScale that monitors every SQL statement that passes through the filter. It measures the duration of that statement, the time between the statement being sent and the first result being returned. The top N times are kept, along with the SQL text itself and a list sorted on the execution times of the query is written to a file upon closure of the client session.
Example minimal configuration:
[MyLogFilter] type=filter module=topfilter [Service] type=service router=readconnroute servers=server1 user=myuser password=mypasswd filters=MyLogFilter
The top filter has one mandatory parameter,
filebase, and a number of optional
The basename of the output file created for each session. The session ID is added to the filename for each file written. This is a mandatory parameter.
The filebase may also be set as the filter, the mechanism to set the filebase via the filter option is superseded by the parameter. If both are set the parameter setting will be used and the filter option ignored.
The number of SQL statements to store and report upon.
The default value for the number of statements recorded is 10.
These regular expression settings limit the queries logged by the top filter.
match=select.*from.*customer.*where exclude=where options=case,extended
The optional source parameter defines an address that is used to match against the address from which the client connection to MariaDB MaxScale originates. Only sessions that originate from this address will be logged.
The optional user parameter defines a user name that is used to match against the user from which the client connection to MariaDB MaxScale originates. Only sessions that are connected using this username will result in results being generated.
Example 1 - Heavily Contended Table
You have an order system and believe the updates of the PRODUCTS table is causing some performance issues for the rest of your application. You would like to know which of the many updates in your application is causing the issue.
Add a filter with the following definition:
[ProductsUpdateTop20] type=filter module=topfilter count=20 match=UPDATE.*PRODUCTS.*WHERE exclude=UPDATE.*PRODUCTS_STOCK.*WHERE filebase=/var/logs/top/ProductsUpdate
Note the exclude entry, this is to prevent updates to the PRODUCTS_STOCK table from being included in the report.
Example 2 - One Application Server is Slow
One of your applications servers is slower than the rest, you believe it is related to database access but you are not sure what is taking the time.
Add a filter with the following definition:
[SlowAppServer] type=filter module=topfilter count=20 source=192.168.0.32 filebase=/var/logs/top/SlowAppServer
In order to produce a comparison with an unaffected application server you can also add a second filter as a control.
[ControlAppServer] type=filter module=topfilter count=20 source=192.168.0.42 filebase=/var/logs/top/ControlAppServer
In the service definition add both filters
[App-Service] type=service router=readconnroute servers=server1 user=myuser password=mypasswd filters=SlowAppServer | ControlAppServer
You will then have two sets of logs files written, one which profiles the top 20 queries of the slow application server and another that gives you the top 20 queries of your control application server. These two sets of files can then be compared to determine what if anything is different between the two.
The following is an example report for a number of fictitious queries executed against the employees example database available for MySQL.
-bash-4.1$ cat /var/logs/top/Employees-top-10.137 Top 10 longest running queries in session. ========================================== Time (sec) | Query -----------+----------------------------------------------------------------- 22.985 | select sum(salary), year(from_date) from salaries s, (select distinct year(from_date) as y1 from salaries) y where (makedate(y.y1, 1) between s.from_date and s.to_date) group by y.y1 5.304 | select d.dept_name as "Department", y.y1 as "Year", count(*) as "Count" from departments d, dept_emp de, (select distinct year(from_date) as y1 from dept_emp order by 1) y where d.dept_no = de.dept_no and (makedate(y.y1, 1) between de.from_date and de.to_date) group by y.y1, d.dept_name order by 1, 2 2.896 | select year(now()) - year(birth_date) as age, gender, avg(salary) as "Average Salary" from employees e, salaries s where e.emp_no = s.emp_no and ("1988-08-01" between from_date AND to_date) group by year(now()) - year(birth_date), gender order by 1,2 2.160 | select dept_name as "Department", sum(salary) / 12 as "Salary Bill" from employees e, departments d, dept_emp de, salaries s where e.emp_no = de.emp_no and de.dept_no = d.dept_no and ("1988-08-01" between de.from_date AND de.to_date) and ("1988-08-01" between s.from_date AND s.to_date) and s.emp_no = e.emp_no group by dept_name order by 1 0.845 | select dept_name as "Department", avg(year(now()) - year(birth_date)) as "Average Age", gender from employees e, departments d, dept_emp de where e.emp_no = de.emp_no and de.dept_no = d.dept_no and ("1988-08-01" between from_date AND to_date) group by dept_name, gender 0.668 | select year(hire_date) as "Hired", d.dept_name, count(*) as "Count" from employees e, departments d, dept_emp de where de.emp_no = e.emp_no and de.dept_no = d.dept_no group by d.dept_name, year(hire_date) 0.249 | select moves.n_depts As "No. of Departments", count(moves.emp_no) as "No. of Employees" from (select de1.emp_no as emp_no, count(de1.emp_no) as n_depts from dept_emp de1 group by de1.emp_no) as moves group by moves.n_depts order by 1 0.245 | select year(now()) - year(birth_date) as age, gender, count(*) as "Count" from employees group by year(now()) - year(birth_date), gender order by 1,2 0.179 | select year(hire_date) as "Hired", count(*) as "Count" from employees group by year(hire_date) 0.160 | select year(hire_date) - year(birth_date) as "Age", count(*) as Count from employees group by year(hire_date) - year(birth_date) order by 1 -----------+----------------------------------------------------------------- Session started Wed Jun 18 18:41:03 2014 Connection from 127.0.0.1 Username massi Total of 24 statements executed. Total statement execution time 35.701 seconds Average statement execution time 1.488 seconds Total connection time 46.500 seconds -bash-4.1$