Jira Data Center is restarting/stuttering because of exceeding database/ multiple connections

Question

How to check if Jira Data Center is stuttering/restarting because it is maxing out its connection pools?

Answer

Look in the atlassian-jira.log file for errors like these:

2018-07-04 13:35:27,101 http-nio-8080-exec-19 url:/rest/api/latest/user  WARN anonymous 815x659873x1 - 172.23.169.71:59200,127.0.0.1 /rest/api/latest/user [c.a.jira.ofbiz.ConnectionPoolHealthSqlInterceptor] 
Dangerous use of multiple connections: taken => count=2; marks=[1-0]; pool=315/50
2018-07-04 13:35:27,101 http-nio-8080-exec-19 url:/rest/api/latest/user  WARN anonymous 815x659873x1 - 172.23.169.71:59200,127.0.0.1 /rest/api/latest/user [c.a.jira.ofbiz.ConnectionPoolHealthSqlInterceptor] 
Dangerous use of multiple connections: replaced => count=1; marks=[0-0]; pool=314/50
2018-07-04 13:35:27,116 http-nio-8080-exec-19 url:/rest/api/latest/user  WARN anonymous 815x659873x1 - 172.23.169.71:59200,127.0.0.1 /rest/api/latest/user [c.a.jira.ofbiz.ConnectionPoolHealthSqlInterceptor] 
Dangerous use of multiple connections: taken => count=2; marks=[1-0]; pool=315/50

2018-07-04 13:35:40,793 http-nio-8080-exec-22 url:/rest/tempo-core/1/expense username:NCrowe  WARN NCrowe 815x659912x3 7g6475 172.23.80.30:56705,127.0.0.1 /rest/tempo-core/1/expense [c.a.jira.ofbiz.ConnectionPoolHealthSqlInterceptor] 
Dangerous use of multiple connections: taken => count=2; marks=[1-0]; pool=315/50
2018-07-04 13:35:40,793 http-nio-8080-exec-22 url:/rest/tempo-core/1/expense username:NCrowe  WARN NCrowe 815x659912x3 7g6475 172.23.80.30:56705,127.0.0.1 /rest/tempo-core/1/expense [c.a.jira.ofbiz.ConnectionPoolHealthSqlInterceptor] 
Dangerous use of multiple connections: replaced => count=1; marks=[0-0]; pool=314/50

And for restarts or Broken connection/Broken pipe errors following this.

If found, client need to talk to Atlassian to understand the reason for this connection pools to be full.

More information that can be useful: https://confluence.atlassian.com/jirakb/jira-slow-with-dangerous-use-of-multiple-connections-error-in-log-229179892.html