Use smaller cache if it cannot allocate

database.py

@@ -227,10 +227,19 @@ class Database(Profiler):
             self.log.warning("Allocating more than 512 MiB of RAM for "
                              "the Ip4 cache is not necessary.")
         max_cache_width = int(math.log2(max(1, max_size*8)))
+        allocated = False
         cache_width = min(2**32, max_cache_width)
+        while not allocated:
+            cache_size = 2**cache_width
+            try:
+                self.ip4cache = numpy.zeros(cache_size, dtype=numpy.bool)
+            except MemoryError:
+                self.log.exception(
+                    "Could not allocate cache. Retrying a smaller one.")
+                cache_width -= 1
+                continue
+            allocated = True
         self.ip4cache_shift = 32-cache_width
-        cache_size = 2**cache_width
-        self.ip4cache = numpy.zeros(cache_size, dtype=numpy.bool)
         for _ in self.exec_each_ip4(self._set_ip4cache):
             pass