[Checkins] [zopefoundation/ZODB] 2729f3: Better IMVCCStorage support

[GitHub]

  Branch: refs/heads/no-more-load
  Home:   https://github.com/zopefoundation/ZODB
  Commit: 2729f3a928ea1bf0cc73cce56bd6bc77c032db30
      https://github.com/zopefoundation/ZODB/commit/2729f3a928ea1bf0cc73cce56bd6bc77c032db30
  Author: Jim Fulton <jim at zope.com>
  Date:   2016-05-04 (Wed, 04 May 2016)

  Changed paths:
    M src/ZODB/Connection.py
    M src/ZODB/tests/MVCCMappingStorage.py
    M src/ZODB/tests/PackableStorage.py

  Log Message:
  -----------
  Better IMVCCStorage support

The previous commit, made in anger, made a test pass, but wasn't
really the right fix.

This commit fixes MVCCMappingStorage's loadBefore implementation by
fixing handling of the internal _ltid variable so that it's updated
during poll_invalidations.  This allowed the base class version of
loadBefore to be used and, I'm 97% sure has the right semantics.
Fixing this revealed a problem with the Connection changes.

Fixed Connection.py to poll for invalidations before computing
_txn_time by calling lastTransaction, so as to get a current value.
We still apply invalidations after computing _txn_time, so that
persistent classes can be loaded correctly when they are invalidated.
This was accomplished by weaving _flush_invalidations into
newTransaction.