Summary

When the confluence.cfg.xml  parameter:

<property name="hibernate.c3p0.preferredTestQuery">select 1</property>

differs in a multi node cluster, the instance tends to create thousands of connections within an hour. Though there is no clear indication where these connections originate from. The default value is set as  "select 1" and if this value defers from node to node, we do tend to see high number of connections with no obvious clue from the server logs.

Environment

Confluence 7.4.7.

Diagnosis

If users notice several thousand connections originating from the application in a short duration and if any typical causes such as plugins, automated APIs or user-action is not causing the issue, please check the following parameter value from all nodes. Also ensure that other factors such as external plugins, automated scripts/APIs or other user actions or not causing this pattern. There may not be any discernible root cause identified from the server logs related to these connections. 

<property name="hibernate.c3p0.preferredTestQuery">select 1</property>

Cause

Not identified at this time.

Solution

Shut down the instances (one node at a time in case of a multi node environment ) and ensure that the following value is the same across nodes and also configure the c3p0 value 0. Restart the node(s)

<property name="hibernate.c3p0.timeout">0</property>
<property name="hibernate.c3p0.preferredTestQuery">select 1</property>