Re: 8 open connections with a pool_size of 7

Stefan Palme wrote at 2009-4-8 18:30 +0200:
>hierzu habe ich nun doch noch mal eine Verständnisfrage (vor allem,
>weil das Problem nach wie vor besteht):

Ich habe diese Woche ein "ZODB-Connection" Leck entdeckt:
PAS (PluggableAuthenticationService) hat Chancen für jedes
"Unauthorited" eine Connection zu verlieren.

Hier eine Beschreibung mit Workaround:

= Introduction =
The upgrade to Zope 2.11 brought us a nasty ZODB connection leak.
The analysis revealed that the leak was caused by `PluginRegistry` in
cooperation with `PluggableAuthService` and Zope's error handling.

`PluggableAuthService` overrides `Response._unauthorized` to call
its `challenge` method. Zope's error handling reraises `Unauthorized`.
This exception is caught by `ZPublisher.publish_module` '''after''' the
transaction has been aborted. `publish_module` reports caught exceptions
by calling `response.exception` which in turn calls `_unauthorized` for
`Unauthorized` exceptions. Thus, `PluggableAuthService.challenge` is
called after the transaction has been aborted. `challenge` calls
`PluginRegistry._getPlugins` which sometimes changes persistent objects.
When this happens, a new transaction is automatically created and the
connection joins this transaction. When later the request is closed,
the ZODB connection refuses to be close because it is still joined
to a transaction. The corresponding exception is caught by Python, a
message is written to `stderr` (usually redirected to `/dev/null`), then
the exception is forgotten,
as it happens inside of a `__del__` method. The only visible effect
is a leaked connection (the one that refused to get closed).

= Feature =
Change `App.ZApplication.Cleanup.__del__` to abort the transaction
before the connection close is closed.



-- 
Dieter


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