From ec370c85daf5e2b63c056ad8b23b54142efb9b3c Mon Sep 17 00:00:00 2001
From: Jim Fulton <jim@zope.com>
Date: Mon, 6 Jun 2016 10:20:17 -0400
Subject: [PATCH] Fixed: the ZEO cache loadBefore method failed to utilize
 current data.

---
 src/ZEO/cache.py            | 30 +++++++++++++++++++++++-------
 src/ZEO/tests/test_cache.py | 19 ++++++++++++++++++-
 2 files changed, 41 insertions(+), 8 deletions(-)

diff --git a/src/ZEO/cache.py b/src/ZEO/cache.py
index 0126dbdce..482a9a7b7 100644
--- a/src/ZEO/cache.py
+++ b/src/ZEO/cache.py
@@ -494,7 +494,7 @@ def getLastTid(self):
     # @defreturn 3-tuple: (string, string, string)
 
     @locked
-    def load(self, oid):
+    def load(self, oid, before_tid=None):
         ofs = self.current.get(oid)
         if ofs is None:
             self._trace(0x20, oid)
@@ -509,6 +509,9 @@ def load(self, oid):
         assert end_tid == z64, (ofs, self.f.tell(), oid, tid, end_tid)
         assert lver == 0, "Versions aren't supported"
 
+        if before_tid and tid >= before_tid:
+            return None
+
         data = read(ldata)
         assert len(data) == ldata, (ofs, self.f.tell(), oid, len(data), ldata)
 
@@ -550,13 +553,22 @@ def load(self, oid):
     def loadBefore(self, oid, before_tid):
         noncurrent_for_oid = self.noncurrent.get(u64(oid))
         if noncurrent_for_oid is None:
-            self._trace(0x24, oid, "", before_tid)
-            return None
+            result = self.load(oid, before_tid)
+            if result:
+                return result[0], result[1], None
+            else:
+                self._trace(0x24, oid, "", before_tid)
+                return result
 
         items = noncurrent_for_oid.items(None, u64(before_tid)-1)
         if not items:
-            self._trace(0x24, oid, "", before_tid)
-            return None
+            result = self.load(oid, before_tid)
+            if result:
+                return result[0], result[1], None
+            else:
+                self._trace(0x24, oid, "", before_tid)
+                return result
+
         tid, ofs = items[-1]
 
         self.f.seek(ofs)
@@ -577,8 +589,12 @@ def loadBefore(self, oid, before_tid):
         assert read(8) == oid, (ofs, self.f.tell(), oid)
 
         if end_tid < before_tid:
-            self._trace(0x24, oid, "", before_tid)
-            return None
+            result = self.load(oid, before_tid)
+            if result:
+                return result[0], result[1], None
+            else:
+                self._trace(0x24, oid, "", before_tid)
+                return result
 
         self._n_accesses += 1
         self._trace(0x26, oid, "", saved_tid)
diff --git a/src/ZEO/tests/test_cache.py b/src/ZEO/tests/test_cache.py
index bff388497..ca69c4210 100644
--- a/src/ZEO/tests/test_cache.py
+++ b/src/ZEO/tests/test_cache.py
@@ -314,7 +314,9 @@ def testChangingCacheSize(self):
             # We use large-2 for the same reason we used small-1 above.
             expected_len = large-2
             self.assertEquals(len(cache), expected_len)
-            expected_oids = set(list(range(11, 50))+list(range(106, 110))+list(range(200, 305)))
+            expected_oids = set(list(range(11, 50)) +
+                                list(range(106, 110)) +
+                                list(range(200, 305)))
             self.assertEquals(set(u64(oid) for (oid, tid) in cache.contents()),
                               expected_oids)
 
@@ -336,6 +338,21 @@ def testSetAnyLastTidOnEmptyCache(self):
         self.cache.setLastTid(p64(3))
         self.cache.setLastTid(p64(4))
 
+    def test_loadBefore_doesnt_miss_current(self):
+        # Make sure that loadBefore get's current data if there
+        # isn't non-current data
+
+        cache = self.cache
+        oid = n1
+        cache.store(oid, n1, None, b'first')
+        self.assertEqual(cache.loadBefore(oid, n1), None)
+        self.assertEqual(cache.loadBefore(oid, n2), (b'first', n1, None))
+        self.cache.invalidate(oid, n2)
+        cache.store(oid, n2, None, b'second')
+        self.assertEqual(cache.loadBefore(oid, n1), None)
+        self.assertEqual(cache.loadBefore(oid, n2), (b'first', n1, n2))
+        self.assertEqual(cache.loadBefore(oid, n3), (b'second', n2, None))
+
 def kill_does_not_cause_cache_corruption():
     r"""