Mysql show no more than 5 concurrent connection

Question

I'm performing some load tests on my brand new server Apache/PHP/Mysql (Bitnami LAMP stack. Php 7.0.3/MySQL 5.7.10 ). I'm using AWS with 1 EC2 instance behind a loadBalancer. At the moment I'm using loader.io or jmeter for the tests. I'm testing a very simple API that perform this query:

select *,sleep(0.5) from debug limit 1

I added the sleep(0.5) because I wanted to see how the server behave with multiple concurrent connections and I found a bottleneck: if I run "SHOW PROCESSLIST" I can see only 5 process even if I have 10 concurrent user. The load test show that the connections are queued because the response time is growing during the test from 500 milliseconds to several seconds (depending on the duration of the test and the number of concurrent users).

I checked

select @@max_connections

and it's 151 (the default). max_user_connections is 0. What other parameter should I check to increase the number of concurrent connection on my DB?

If I run the test with 5 concurrent users, each one get a response in 500 milliseconds. If I add more concurrent users than the response time slow down.

If I run the load test on an API that does not access the DB there are no issues even with 400 concurrent users.

EDIT:

Monitoring with HTOP I see:

Tasks: 34, 245 thr; 2 running

Could be here the issue?

Thanks a lot

Can you please describe your PHP/MySQL server in more details? What web server are you using? Apache module, CGI, FCGI? — CodeZombie
How are you running your concurrent tests? Have you tried making the sleep longer to guarantee that the query sticks around long enough? — Mr. Llama
This query will only sleep if there is at least one row of data in the debug table. Also check MAX_USER_CONNECTIONS for the user is also zero as it can be set per user. — Steve E.
I updated the description. I'm using Apache. What do you mean with "guarantee that the query sticks around long enough"? — Stefano Giacone
@Steve: MAX_USER_CONNECTIONS is 0 and there is 1 row of data. If I run the test with 5 concurrent users each one get a response in 500 milliseconds — Stefano Giacone

Somnath Muluk Somnath Muluk · Accepted Answer · 2016-02-24T06:15:18

There are two areas for allowing concurrent connections:

1. Web servers

Check number of concurrent connections allowed by your web server.

See

Select your web server wisely to handle more concurrent connections.

2. Database and Open Files

Check your MySQL DB is capable of handling max concurrent connection coming from WebServer PHP.

Set max_connections to some higher amount.

set global max_connections := 800;

Also check open_files_limit for your OS. On linux, your process is limited to 1024 files, by default. This is very low, since every thread, connection, and, of course, file -- make for a file handle in linux. So set open_files_limit to some generous number (say 10000) to clear up your many connections with the operating system.

Mysql show no more than 5 concurrent connection

2 Answers