Allow LRUSizeTrackingCache to have a max size of 0.

Allowing 1 byte, but disallowing 0 bytes is somewhat silly.

PiperOrigin-RevId: 871814019
Change-Id: I6ebbea20d449bc0c77dc20e8e75615d06b26f76e

Author: svsgoogle

py/koladata/ext/persisted_data/lru_size_tracking_cache.py

@@ -78,9 +78,9 @@ def __init__(
         that the cache should hold. The cache will evict the least recently used
         entries to ensure that it never exceeds this limit.
     """
-    if max_total_bytes_of_entries_in_cache <= 0:
+    if max_total_bytes_of_entries_in_cache < 0:
       raise ValueError(
-          'max_total_bytes_of_entries_in_cache must be positive, but is'
+          'max_total_bytes_of_entries_in_cache must be non-negative, but is'
           f' {max_total_bytes_of_entries_in_cache}'
       )
 
@@ -155,9 +155,9 @@ def set_max_total_bytes_of_entries_in_cache(
       self, max_total_bytes_of_entries_in_cache: int
   ) -> None:
     """Sets the limit on the total size of all entries in the cache."""
-    if max_total_bytes_of_entries_in_cache <= 0:
+    if max_total_bytes_of_entries_in_cache < 0:
       raise ValueError(
-          'max_total_bytes_of_entries_in_cache must be positive, but is'
+          'max_total_bytes_of_entries_in_cache must be non-negative, but is'
           f' {max_total_bytes_of_entries_in_cache}'
       )
     with self._rlock:

py/koladata/ext/persisted_data/lru_size_tracking_cache_test.py

@@ -114,24 +114,29 @@ def test_basic_functionality(self):
     self.assertIsNone(cache.get('d'))
     self.assertIsNone(cache.get('e'))
 
-    # Setting the max size to a non-positive value raises an error.
-    with self.assertRaises(ValueError):
-      cache.set_max_total_bytes_of_entries_in_cache(0)
+    # Setting the max size to a negative value raises an error.
     with self.assertRaises(ValueError):
       cache.set_max_total_bytes_of_entries_in_cache(-1)
     # The max size is not changed.
     self.assertEqual(cache.get_max_total_bytes_of_entries_in_cache(), 10)
 
-    # Creating a new cache with a non-positive max size raises an error.
-    with self.assertRaises(ValueError):
-      lru_size_tracking_cache.LruSizeTrackingCache(
-          max_total_bytes_of_entries_in_cache=0,
-      )
+    # Using zero is fine and evicts all entries, thereby disabling caching.
+    cache.set_max_total_bytes_of_entries_in_cache(0)
+    self.assertEqual(cache.get_max_total_bytes_of_entries_in_cache(), 0)
+
+    # Creating a new cache with a negative max size raises an error.
     with self.assertRaises(ValueError):
       lru_size_tracking_cache.LruSizeTrackingCache(
           max_total_bytes_of_entries_in_cache=-1,
       )
 
+    # We can create a cache with zero max size. Such a cache is not very useful
+    # unless we plan to increase the max size later.
+    cache = lru_size_tracking_cache.LruSizeTrackingCache(
+        max_total_bytes_of_entries_in_cache=0,
+    )
+    self.assertEqual(cache.get_max_total_bytes_of_entries_in_cache(), 0)
+
 
 if __name__ == '__main__':
   absltest.main()