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https://github.com/element-hq/synapse
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SYN-369: Add comments to the sequence number logic in the cache
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1 changed files with 7 additions and 0 deletions
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@ -98,6 +98,8 @@ class Cache(object):
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def update(self, sequence, *args):
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def update(self, sequence, *args):
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self.check_thread()
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self.check_thread()
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if self.sequence == sequence:
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if self.sequence == sequence:
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# Only update the cache if the caches sequence number matches the
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# number that the cache had before the SELECT was started (SYN-369)
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self.prefill(*args)
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self.prefill(*args)
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def prefill(self, *args): # because I can't *keyargs, value
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def prefill(self, *args): # because I can't *keyargs, value
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@ -117,6 +119,8 @@ class Cache(object):
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self.check_thread()
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self.check_thread()
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if len(keyargs) != self.keylen:
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if len(keyargs) != self.keylen:
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raise ValueError("Expected a key to have %d items", self.keylen)
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raise ValueError("Expected a key to have %d items", self.keylen)
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# Increment the sequence number so that any SELECT statements that
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# raced with the INSERT don't update the cache (SYN-369)
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self.sequence += 1
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self.sequence += 1
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self.cache.pop(keyargs, None)
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self.cache.pop(keyargs, None)
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@ -159,6 +163,9 @@ def cached(max_entries=1000, num_args=1, lru=False):
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raise ValueError("Stale cache entry")
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raise ValueError("Stale cache entry")
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defer.returnValue(cached_result)
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defer.returnValue(cached_result)
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except KeyError:
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except KeyError:
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# Get the sequence number of the cache before reading from the
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# database so that we can tell if the cache is invalidated
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# while the SELECT is executing (SYN-369)
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sequence = cache.sequence
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sequence = cache.sequence
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ret = yield orig(self, *keyargs)
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ret = yield orig(self, *keyargs)
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