Background My gevent application hangs after issuing a query that yields 1000+ rows and then a COMMIT. After fixing mysqlclient (see Python mysqlclient Doesn’t Work Well with gevent), the COMMIT does not hang the whole application, but it still hangs the greenlet that issues the SQL query.
Setup: Ubuntu 16.04, ProxySQL v1.4.13, Amazon RDS MySQL 5.6 (ProxySQL backend), Python 2.7.12 application running on the same machine as ProxySQL
Symptoms It is always reproducible with the specific query, the backend, and on that machine.Update 21 Mar 2019 There’s a new post Fixing ProxySQL Idle Threads Epoll Hang Heisenbug about fixing a bug of ProxySQL when --idle-threads is enabled.
Problem ProxySQL does not scale with high numbers of connections by default. When there are tens of thousands of client connection to ProxySQL, the CPU usage of ProxySQL may go up to 300%+ because by default it uses 4 threads. Even with 3000 mostly idle connections, it hits ~70% CPU usage.