diff --git a/synapse/util/caches/dictionary_cache.py b/synapse/util/caches/dictionary_cache.py
index cb6933c61c..d4105822b3 100644
--- a/synapse/util/caches/dictionary_cache.py
+++ b/synapse/util/caches/dictionary_cache.py
@@ -23,7 +23,17 @@ import logging
logger = logging.getLogger(__name__)
-class DictionaryEntry(namedtuple("DictionaryEntry", ("full", "value"))):
+class DictionaryEntry(namedtuple("DictionaryEntry", ("full", "known_absent", "value"))):
+ """Returned when getting an entry from the cache
+
+ Attributes:
+ full (bool): Whether the cache has the full or dict or just some keys.
+ If not full then not all requested keys will necessarily be present
+ in `value`
+ known_absent (set): Keys that were looked up in the dict and were not
+ there.
+ value (dict): The full or partial dict value
+ """
def __len__(self):
return len(self.value)
@@ -58,21 +68,31 @@ class DictionaryCache(object):
)
def get(self, key, dict_keys=None):
+ """Fetch an entry out of the cache
+
+ Args:
+ key
+ dict_key(list): If given a set of keys then return only those keys
+ that exist in the cache.
+
+ Returns:
+ DictionaryEntry
+ """
entry = self.cache.get(key, self.sentinel)
if entry is not self.sentinel:
self.metrics.inc_hits()
if dict_keys is None:
- return DictionaryEntry(entry.full, dict(entry.value))
+ return DictionaryEntry(entry.full, entry.known_absent, dict(entry.value))
else:
- return DictionaryEntry(entry.full, {
+ return DictionaryEntry(entry.full, entry.known_absent, {
k: entry.value[k]
for k in dict_keys
if k in entry.value
})
self.metrics.inc_misses()
- return DictionaryEntry(False, {})
+ return DictionaryEntry(False, set(), {})
def invalidate(self, key):
self.check_thread()
@@ -87,19 +107,34 @@ class DictionaryCache(object):
self.sequence += 1
self.cache.clear()
- def update(self, sequence, key, value, full=False):
+ def update(self, sequence, key, value, full=False, known_absent=None):
+ """Updates the entry in the cache
+
+ Args:
+ sequence
+ key
+ value (dict): The value to update the cache with.
+ full (bool): Whether the given value is the full dict, or just a
+ partial subset there of. If not full then any existing entries
+ for the key will be updated.
+ known_absent (set): Set of keys that we know don't exist in the full
+ dict.
+ """
self.check_thread()
if self.sequence == sequence:
# Only update the cache if the caches sequence number matches the
# number that the cache had before the SELECT was started (SYN-369)
+ if known_absent is None:
+ known_absent = set()
if full:
- self._insert(key, value)
+ self._insert(key, value, known_absent)
else:
- self._update_or_insert(key, value)
+ self._update_or_insert(key, value, known_absent)
- def _update_or_insert(self, key, value):
- entry = self.cache.setdefault(key, DictionaryEntry(False, {}))
+ def _update_or_insert(self, key, value, known_absent):
+ entry = self.cache.setdefault(key, DictionaryEntry(False, set(), {}))
entry.value.update(value)
+ entry.known_absent.update(known_absent)
- def _insert(self, key, value):
- self.cache[key] = DictionaryEntry(True, value)
+ def _insert(self, key, value, known_absent):
+ self.cache[key] = DictionaryEntry(True, known_absent, value)
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