Merge pull request #4 from mamico/patch-1

[BACKPORT] Avoid potentially expensive `len()` call in value index estimation
zopefoundation · Oct 9, 2014 · e8a1e19 · e8a1e19
2 parents 91bba1a + 7bd631e
commit e8a1e19
Showing 1 changed file with 9 additions and 1 deletion.
diff --git a/src/Products/ZCatalog/plan.py b/src/Products/ZCatalog/plan.py
@@ -201,7 +201,15 @@ def valueindexes(self):
         for name, index in indexes.items():
             if IUniqueValueIndex.providedBy(index):
                 values = index.uniqueValues()
-                if values and len(list(values)) < MAX_DISTINCT_VALUES:
+                i = 0
+                for value in values:
+                    # the total number of unique values might be large and
+                    # expensive to load, so we only check if we can get
+                    # more than MAX_DISTINCT_VALUES
+                    if i >= MAX_DISTINCT_VALUES:
+                        break
+                    i += 1
+                if i > 0 and i < MAX_DISTINCT_VALUES:
                     # Only consider indexes which actually return a number
                     # greater than zero
                     value_indexes.add(name)