While working on bug 1334874, bug 1337865 and bug 1342745 which tried to stop leaking nsMsgDBFolder (and nsMsgNewsFolder) objects since their leakage causes the "dynamic atoms leak" assertion, we noticed - what was known before - that various databases also leak, for example running mozilla/mach xpcshell-test mailnews/base/test/unit/test_nsMsgDBView.js gives "[4932] WARNING: some msg dbs left open: '!m_dbCache.Length()', file c:/mozilla-source/comm-central/mailnews/db/msgdb/src/nsMsgDatabase.cpp, line 87" "db left open c:\\users\\jorgk\\appdata\\local\\temp\\firefox\\xpcshellprofile\\Mail\\Local Folders\\Trash.msf" "db left open c:\\users\\jorgk\\appdata\\local\\temp\\firefox\\xpcshellprofile\\Mail\\Local Folders\\gabba0.msf" (and more) In fact, looking for this warning in a recent Xpcshell test log I found this warning eight times (which not as bad as I thought). It's about time we look into this problem. Chiaki, I know you've been alerting us to this problem for a long time, so finally the penny has dropped ;-) Please don't paste long logs into comments here, if you have logs that you think might help us, please attach them.

Great I will look into this issue finally this week.

From my experiments, the database left open seems to always be the one last one that was open in the window and a message was viewed in it.

(In reply to :aceman from comment #2) > From my experiments, the database left open seems to always be the one last > one that was open in the window and a message was viewed in it. Hmm, I looked at warnings in Xpcshell tests and they don't view a message in a window ;-) BTW, we're down to six of these warnings, all from failing tests from bug 1342745. I've just looked at a Mozmill run and there are also six of these warnings.

Hmm, that stuff is a mystery: Always looking at Windows debug X and Z: First number: Matches on: m_dbCache.Length, second number: Matches on: "left open" Fri Mar 03, 2017 18:05:57 - X:6 - Z:18 - 168 Fri Mar 03, 2017 19:56:17 - X:6 - Z:19 - 171 Mon Mar 06, 2017 11:16:18 - X:6 - Z:17 - 144 Tue Mar 07, 2017 18:44:22 - X:0 - Z:0 - Zero!! Wed Mar 08, 2017 09:00:10 - X:0 - Z:18 - 170 Skipping to the present: Sat Apr 22, 2017 0:53:25 - X:0 - Z:18 - 82 After landing bug 853881: Sat Apr 22, 2017 08:49:35 - X:? - Z:16 - 58 Some try results: Note that with patch (v4) of bug 853881 I get Z: 16 - 59, with patch (v3) it's Z: 18 - 80, but maybe that's because with (v4) the application crashes and some tests aren't run.

Some figures on the 1st of July 2017: Matches on: m_dbCache.Length: 18 Matches on: left open: 187!!! So something has changed in cycle collection. Also, debug builds now crash after reporting the left-open databases, see bug 1377692.