Bugs Fixed:

  2 BTree bugs, introduced by a bug fix in 3.9.0c2, sometimes caused
  deletion of keys to be improperly handled, resulting in data being
  available via iteraation but not item access.

src/BTrees/BTreeTemplate.c

@@ -720,6 +720,7 @@ _BTree_set(BTree *self, PyObject *keyarg, PyObject *value,
           COPY_KEY(d->key, bucket->keys[0]);
           INCREF_KEY(d->key);
           PER_UNUSE(bucket);
+          if (PER_CHANGED(self) < 0) goto Error;
         }
     }
 

src/BTrees/MergeTemplate.c

@@ -160,6 +160,15 @@ bucket_merge(Bucket *s1, Bucket *s2, Bucket *s3)
             }
           else if (set || (TEST_VALUE(i1.value, i2.value) == 0))
             {                   /* deleted in i3 */
+              if (i3.position == 1)
+                {
+                  /* Deleted the first item.  This will modify the
+                     parent node, so we don't know if merging will be
+                     safe
+                  */
+                  merge_error(i1.position, i2.position, i3.position, 13);
+                  goto err;
+                }
               if (i1.next(&i1) < 0) goto err;
               if (i2.next(&i2) < 0) goto err;
             }
@@ -178,6 +187,15 @@ bucket_merge(Bucket *s1, Bucket *s2, Bucket *s3)
             }
           else if (set || (TEST_VALUE(i1.value, i3.value) == 0))
             {                   /* deleted in i2 */
+              if (i2.position == 1)
+                {
+                  /* Deleted the first item.  This will modify the
+                     parent node, so we don't know if merging will be
+                     safe
+                  */
+                  merge_error(i1.position, i2.position, i3.position, 13);
+                  goto err;
+                }
               if (i1.next(&i1) < 0) goto err;
               if (i3.next(&i3) < 0) goto err;
             }

src/BTrees/tests/testBTrees.py

@@ -1975,7 +1975,11 @@ class InternalKeysMappingTest(TestCase):
         with bucket children.
         """
 
-        tree = self.t_class()
+        from ZODB.MappingStorage import DB
+        db = DB()
+        conn = db.open()
+
+        tree = conn.root.tree = self.t_class()
         i = 0
 
         # Grow the btree until we have multiple buckets
@@ -1986,12 +1990,17 @@ class InternalKeysMappingTest(TestCase):
             if len(data) >= 3:
                 break
 
+        transaction.commit()
+
         # Now, delete the internal key and make sure it's really gone
         key = data[1]
         del tree[key]
         data = tree.__getstate__()[0]
         self.assert_(data[1] != key)
 
+        # The tree should have changed:
+        self.assert_(tree._p_changed)
+
         # Grow the btree until we have multiple levels
         while 1:
             i += 1
@@ -2007,6 +2016,9 @@ class InternalKeysMappingTest(TestCase):
         data = tree.__getstate__()[0]
         self.assert_(data[1] != key)
 
+        transaction.abort()
+        db.close()
+
 class InternalKeysSetTest:
     """There must not be any internal keys not in the TreeSet
     """

src/BTrees/tests/testConflict.py

@@ -49,6 +49,7 @@ class Base:
         n = 'fs_tmp__%s' % os.getpid()
         self.storage = FileStorage(n)
         self.db = DB(self.storage)
+        return self.db
 
 class MappingBase(Base):
     """ Tests common to mappings (buckets, btrees) """
@@ -102,11 +103,11 @@ class MappingBase(Base):
 
     def testMergeDelete(self):
         base, b1, b2, bm, e1, e2, items = self._setupConflict()
-        del b1[items[0][0]]
+        del b1[items[1][0]]
         del b2[items[5][0]]
         del b1[items[-1][0]]
         del b2[items[-2][0]]
-        del bm[items[0][0]]
+        del bm[items[1][0]]
         del bm[items[5][0]]
         del bm[items[-1][0]]
         del bm[items[-2][0]]
@@ -114,11 +115,11 @@ class MappingBase(Base):
 
     def testMergeDeleteAndUpdate(self):
         base, b1, b2, bm, e1, e2, items = self._setupConflict()
-        del b1[items[0][0]]
+        del b1[items[1][0]]
         b2[items[5][0]]=1
         del b1[items[-1][0]]
         b2[items[-2][0]]=2
-        del bm[items[0][0]]
+        del bm[items[1][0]]
         bm[items[5][0]]=1
         del bm[items[-1][0]]
         bm[items[-2][0]]=2
@@ -237,11 +238,11 @@ class SetTests(Base):
 
     def testMergeDelete(self):
         base, b1, b2, bm, e1, e2, items = self._setupConflict()
-        b1.remove(items[0])
+        b1.remove(items[1])
         b2.remove(items[5])
         b1.remove(items[-1])
         b2.remove(items[-2])
-        bm.remove(items[0])
+        bm.remove(items[1])
         bm.remove(items[5])
         bm.remove(items[-1])
         bm.remove(items[-2])
@@ -331,8 +332,8 @@ def test_merge(o1, o2, o3, expect, message='failed to merge', should_fail=0):
         assert merged == expected, message
 
 class NastyConfict(Base, TestCase):
-    def setUp(self):
-        self.t = OOBTree()
+
+    t_type = OOBTree
 
     # This tests a problem that cropped up while trying to write
     # testBucketSplitConflict (below):  conflict resolution wasn't
@@ -765,6 +766,68 @@ class NastyConfict(Base, TestCase):
         else:
             self.fail("expected ConflictError")
 
+    def testConflictOfInsertAndDeleteOfFirstBucketItem(self):
+        """
+        Recently, BTrees became careful about removing internal keys
+        (keys in internal aka BTree nodes) when they were deleted from
+        buckets. This poses a problem for conflict resolution.
+
+        We want to guard against a case in which the first key in a
+        bucket is removed in one transaction while a key is added
+        after that key but before the next key in another transaction
+        with the result that the added key is unreachble
+
+        original:
+
+          Bucket(...), k1, Bucket((k1, v1), (k3, v3), ...)
+
+        tran1
+
+          Bucket(...), k3, Bucket(k3, v3), ...)
+
+        tran2
+
+          Bucket(...), k1, Bucket((k1, v1), (k2, v2), (k3, v3), ...)
+
+          where k1 < k2 < k3
+
+        We don't want:
+
+          Bucket(...), k3, Bucket((k2, v2), (k3, v3), ...)
+
+          as k2 would be unfindable, so we want a conflict.
+
+        """
+        mytype = self.t_type
+        db = self.openDB()
+        tm1 = transaction.TransactionManager()
+        conn1 = db.open(tm1)
+        conn1.root.t = t = mytype()
+        for i in range(0, 200, 2):
+            t[i] = i
+        tm1.commit()
+        k = t.__getstate__()[0][1]
+        assert t.__getstate__()[0][2].keys()[0] == k
+
+        tm2 = transaction.TransactionManager()
+        conn2 = db.open(tm2)
+
+        t[k+1] = k+1
+        del conn2.root.t[k]
+        for i in range(200,300):
+            conn2.root.t[i] = i
+
+        tm1.commit()
+        self.assertRaises(ConflictError, tm2.commit)
+        tm2.abort()
+
+        k = t.__getstate__()[0][1]
+        t[k+1] = k+1
+        del conn2.root.t[k]
+
+        tm2.commit()
+        self.assertRaises(ConflictError, tm1.commit)
+        tm1.abort()
 
 def test_suite():
     suite = TestSuite()

src/CHANGES.txt

@@ -2,6 +2,16 @@
  Change History
 ================
 
+3.9.3 (2009-10-??)
+==================
+
+Bugs Fixed
+----------
+
+- 2 BTree bugs, introduced by a bug fix in 3.9.0c2, sometimes caused
+  deletion of keys to be improperly handled, resulting in data being
+  available via iteraation but not item access.
+
 3.9.2 (2009-10-13)
 ==================
 

src/ZODB/POSException.py

@@ -214,6 +214,9 @@ class BTreesConflictError(ConflictError):
 
             # 12; i2 or i3 was empty
             'Empty bucket in a transaction',
+
+            # 13; delete of first key, which causes change to parent node
+            'Delete of first key',
             ]
 
     def __init__(self, p1, p2, p3, reason):