[ZODB-Dev] RelStorage breaks history tab - solution?

[Chris Withers]

Hi Shane,

On 23/05/2012 16:27, Chris Withers wrote:
> Okay, the issue appears to be that, in some circumstances, RelStorage is
> leaving the read connection with an open transaction that isn't rolled
> back.

Upon investigation, this turns out to be the history method itself! :-)

Switching to the following patch also solves the problem:

diff --git a/relstorage/storage.py b/relstorage/storage.py
index 2d592d3..3fa792b 100644
--- a/relstorage/storage.py
+++ b/relstorage/storage.py
@@ -1053,6 +1053,7 @@ class RelStorage(
                          break
              return res
          finally:
+            self._load_conn.rollback()
              self._lock_release()

      def undo(self, transaction_id, transaction):

However, that raised more questions for me:

- How does RelStorage usually rollback the _load_conn in a non-write 
transaction?

- Why doesn't this kick in when viewing the history method?

My guess as to why 
ZODB.tests.HistoryStorage:HistoryStorage.checkSimpleHistory passes is 
that everything is done with the same thread/connection, and so a 
consistent view of the data is seen.

More confusing: having dropped the zserver-threads down to one and from 
looking at the results of:

select * from pg_catalog.pg_stat_activity where datname='myrelstorage';

...it appears that there's:

- one connection for reads

- one connection for writes, which is opened when first used.

Okay, as expected.

- one connection for viewing history.

I can't see where/why this final connection is opened...

Shane, little help?

Chris

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