This is so true and easy to overlook until a post mortem. A great exercise is to audit how connections are maintained in your application, before it's too late.
Re:About Database Connection Pool Sizing
by macintux on Monday November 12, 2018 @12:46PM
(#18434136)
I'm reminded of a systems failure described in, IIRC, the O'Reilly book "Release It!". Java ODBC exception swallowed resulted in eventually running out of connections.
Very tough problem to troubleshoot without extensive monitoring.
One of the most common performance errors I see in random http applications is grabbing db connections for too long, like in middleware, or too aggressively in parallel queries.