• Tim Peters's avatar
    Merge rev 28701 from 3.3 branch. · 743ef117
    Tim Peters authored
    Critical bugfix for invalidations during ZEO cache verification.
    
    ClientCache.invalidate():
    
    - This was written not to expect tid=None, which is what happens
      during cache verification, although it didn't catch the tid=None
      case and went on doing really strange things then.  Rewrote so
      that tid=None means "forget everything I think I know about
      the oid".  It was kind-of performing an invalidation wrt the
      in-memory data structures in this case, but leaving the
      invalidated data for oid looking as if it were still current on
      disk.  That was accidental, depending on what various other
      parts of the code thought "None" meant (primarily, an end_tid
      of None is generally taken here to mean "the data is current").
      
    - Also changed the "and we already have version data for oid" case
      to a "forget everything I think I know about the oid" case.  The
      comments seemed to say that's what it thought it was doing, but
      the code actually left non-current revisions sitting around.  I
      really don't want to spend time trying to figure out what versions
      are supposed to do in all cases here, and nuking everything in
      this case is an obviously *safe* thing to do.
    
    - Added more asserts, because the pre- and post-conditions here are
      delicate and non-obvious (indeed, that a new assert failed is how
      I stumbled into the invalidation problem to begin with).
    
    FileCache.remove():  Changed to remove the key from self.key2entry.
    While self.filemap keeps an in-memory map of the entire disk file,
    there's no need to keep info in key2entry for keys that no longer
    exist in the disk file.  I'm not sure a visible bug followed from
    this (but not sure one didn't either!), but it at best wasted
    memory, and violated a documented invariant.
    
    ConnectionTests.py:  New test checkVerificationInvalidationPersists().
    Before the patch, this provokes a persistent ZEO cache into
    delivering stale object state.  Of course the test passes after
    this patch.
    
    stats.py:  Added a trace code meaning "invalidation hit, and the
    object state was discarded".  This is what happens now for
    invalidations produced by verification.  Because of MVCC, that's
    really not needed *except* for the invalidations produced by
    startup verification (invalidations normally just set a new
    ending tid on the validity range for what was current data; but
    validity-range info isn't available from verification invalidations).
    
    743ef117
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