def __init__(self, maxlen, **kwargs):
# ARC has two caches: a recency cache and a frequency cache
self._recency_cache_top = LinkedSet() # paper: T_1
self._recency_cache_bottom = LinkedSet() # paper: B_1
self._frequency_cache_top = LinkedSet() # paper: T_2
self._frequency_cache_bottom = LinkedSet() # paper: B_2
self._maxlen = int(maxlen) # paper: c
if self._maxlen <= 0:
raise ValueError('maxlen must be positive')
# _p is the target number of elements for the recency cache top
# which means that _maxlen - _p is the target number of elements for the frequency cache top
# It is the target number since it will be a real number at some point and not a natural number.
self._p = 0
def __init__(self, maxlen, **kwargs):
# ARC has two caches: a recency cache and a frequency cache
self._recency_cache_top = LinkedSet() # paper: T_1
self._recency_cache_bottom = LinkedSet() # paper: B_1
self._frequency_cache_top = LinkedSet() # paper: T_2
self._frequency_cache_bottom = LinkedSet() # paper: B_2
self._maxlen = int(maxlen) # paper: c
if self._maxlen <= 0:
raise ValueError('maxlen must be positive')
# _p is the target number of elements for the recency cache top
# which means that _maxlen - _p is the target number of elements for the frequency cache top
# It is the target number since it will be a real number at some point and not a natural number.
self._p = 0
class AdaptiveReplacementCache(Cache):
"""Adaptive Replacement Cache (ARC) eviction policy from
Megiddo, Nimrod, and Dharmendra S. Modha.
"ARC: A Self-Tuning, Low Overhead Replacement Cache."
FAST. Vol. 3. 2003.
"ARC dynamically, adaptively, and continually balances between the recency and frequency components in an online
and self-tuning fashion" (from the paper above)
ARC uses two different lists with observed elements, one of which is based on recently (and only once) observed
elements and one of which is based on frequently (and at least twice) observed elements. The number of observed
elements is twice the actual cache size and the percentage of elements in the actual cache from the two lists
varies based on the stream of requests. In the implementation, the two lists are actually realized as two lists
each with a top part and a bottom part. The top part corresponds to the part of the list that is in the actual
cache, while the bottom part consists solely of observed elements that are not in the cache.
"""
@inheritdoc(Cache)
def __init__(self, maxlen, **kwargs):
# ARC has two caches: a recency cache and a frequency cache
self._recency_cache_top = LinkedSet() # paper: T_1
self._recency_cache_bottom = LinkedSet() # paper: B_1
self._frequency_cache_top = LinkedSet() # paper: T_2
self._frequency_cache_bottom = LinkedSet() # paper: B_2
self._maxlen = int(maxlen) # paper: c
if self._maxlen <= 0:
raise ValueError('maxlen must be positive')
# _p is the target number of elements for the recency cache top
# which means that _maxlen - _p is the target number of elements for the frequency cache top
# It is the target number since it will be a real number at some point and not a natural number.
self._p = 0
@inheritdoc(Cache)
def __len__(self):
return self._frequency_cache_top.__len__() + self._recency_cache_top.__len__()
@property
@inheritdoc(Cache)
def maxlen(self):
return self._maxlen
@inheritdoc(Cache)
def dump(self):
top_parts = deepcopy(list(self._frequency_cache_top))
top_parts.extend(list(self._recency_cache_top))
return top_parts
def position(self, k):
"""Return the current position of an item in the cache. Position *0*
refers to the head of the frequency cache (i.e. most recently used item
that was used at least twice) if there is an element in the frequency cache.
This method does not change the internal state of the cache.
Parameters
----------
k : any hashable type
The item looked up in the cache
Returns
-------
position : int
The current position of the item in the cache
"""
if k in self._frequency_cache_top:
return self._frequency_cache_top.index(k)
elif k in self._recency_cache_top:
return self._recency_cache_top.index(k) + self._frequency_cache_top.__len__()
else:
raise ValueError('The item %s is not in the cache' % str(k))
@inheritdoc(Cache)
def has(self, k):
if k in self._frequency_cache_top:
return True
elif k in self._recency_cache_top:
return True
else:
return False
@inheritdoc(Cache)
def get(self, k, weight):
# two basic cases:
# 1. cache hit
# 2. cache miss
if not self.has(k):
# cache miss - do not change state of cache (subsequent put() operation can do that)
return False
else:
# cache hit - change state of cache by moving up k
if k in self._recency_cache_top:
# move k to top of frequency cache
self._recency_cache_top.remove(k)
self._frequency_cache_top.append_top(k)
else: # k is in frequency cache
self._frequency_cache_top.move_to_top(k)
return True
def put(self, k, weight):
"""Register an item's occurrence with the cache if not already inserted.
This operation changes the state of the cache in that it might influence
the number of elements taken from the recency and frequency caches and
possibly replace an element from one of them.
If the element is already present in the cache, it will pushed to the
top of the cache.
Parameters
----------
k : any hashable type
The item to be inserted
weight : int
The weight of the item (not used here)
Returns
-------
evicted : any hashable type
The evicted object or *None* if no contents were evicted.
"""
# in case of k already being cached, move it to the top of the frequency cache
if self.get(k, weight):
return None
# there are three cases:
# 1. k is in bottom of recency cache (i.e. not cached, only observed)
# 2. k is in bottom of frequency cache (i.e. not cached, only observed)
# 3. k is in neither of the caches (i.e. neither cached nor observed)
if k in self._recency_cache_bottom:
rec = self._recency_cache_bottom.__len__()
freq = self._frequency_cache_bottom.__len__()
delta = 1 if rec >= freq else float(freq) / float(rec)
self._p = min(self._p + delta, self._maxlen)
evicted = self._replace(k, self._p)
self._recency_cache_bottom.remove(k)
self._frequency_cache_top.append_top(k)
return evicted
elif k in self._frequency_cache_bottom:
rec = self._recency_cache_bottom.__len__()
freq = self._frequency_cache_bottom.__len__()
delta = 1 if freq >= rec else float(rec) / float(freq)
self._p = max(self._p - delta, 0)
evicted = self._replace(k, self._p)
self._frequency_cache_bottom.remove(k)
self._frequency_cache_top.append_top(k)
return evicted
else:
# there are two subcases:
# A) recency cache has _maxlen elements, i.e. it is full
# B) recency cache is not full yet
# only in some cases an eviction takes place so the default value is set to None
evicted = None
# A) recency cache full
if self._recency_cache_top.__len__() + self._recency_cache_bottom.__len__() == self._maxlen:
if self._recency_cache_top.__len__() < self._maxlen:
# the actual eviction is from the top of the recency or frequency cache
# dropping from the bottom is not an eviction, it is merely the end of observation
self._recency_cache_bottom.pop_bottom()
evicted = self._replace(k, self._p)
else: # bottom of recency cache is empty
evicted = self._recency_cache_top.pop_bottom()
# B) recency cache not full yet
else:
total_observed = self._frequency_cache_top.__len__() + self._frequency_cache_bottom.__len__() + \
self._recency_cache_top.__len__() + self._recency_cache_bottom.__len__()
if total_observed >= self._maxlen:
if total_observed == 2 * self._maxlen:
self._frequency_cache_bottom.pop_bottom()
evicted = self._replace(k, self._p)
else:
# if the number of observed elements is less than the actual cache size, no removals are necessary
pass
self._recency_cache_top.append_top(k)
return evicted
def _replace(self, k, p):
# REPLACE subroutine from paper - to be used internally only
rec_top_len = self._recency_cache_top.__len__()
if rec_top_len > 0 and (rec_top_len > p or (k in self._frequency_cache_bottom and rec_top_len == p)):
evicted = self._recency_cache_top.pop_bottom()
self._recency_cache_bottom.append_top(evicted)
return evicted
else:
evicted = self._frequency_cache_top.pop_bottom()
self._frequency_cache_bottom.append_top(evicted)
return evicted
@inheritdoc(Cache)
def remove(self, k):
if k in self._frequency_cache_top:
self._frequency_cache_top.remove(k)
return True
elif k in self._frequency_cache_bottom:
self._frequency_cache_bottom.remove(k)
return True
elif k in self._recency_cache_top:
self._recency_cache_top.remove(k)
return True
elif k in self._recency_cache_bottom:
self._recency_cache_bottom.remove(k)
return True
else:
return False
@inheritdoc(Cache)
def clear(self):
self._frequency_cache_bottom.clear()
self._frequency_cache_top.clear()
self._recency_cache_bottom.clear()
self._recency_cache_top.clear()
self._p = 0
def get_p(self):
return self._p
def print_internal_dump(self):
print(("%s %s %s %s" % (str(self._recency_cache_bottom), str(self._recency_cache_top),
str(self._frequency_cache_bottom), str(self._frequency_cache_top))))
class AdaptiveReplacementCache(Cache):
"""Adaptive Replacement Cache (ARC) eviction policy from
Megiddo, Nimrod, and Dharmendra S. Modha.
"ARC: A Self-Tuning, Low Overhead Replacement Cache."
FAST. Vol. 3. 2003.
"ARC dynamically, adaptively, and continually balances between the recency and frequency components in an online
and self-tuning fashion" (from the paper above)
ARC uses two different lists with observed elements, one of which is based on recently (and only once) observed
elements and one of which is based on frequently (and at least twice) observed elements. The number of observed
elements is twice the actual cache size and the percentage of elements in the actual cache from the two lists
varies based on the stream of requests. In the implementation, the two lists are actually realized as two lists
each with a top part and a bottom part. The top part corresponds to the part of the list that is in the actual
cache, while the bottom part consists solely of observed elements that are not in the cache.
"""
@inheritdoc(Cache)
def __init__(self, maxlen, **kwargs):
# ARC has two caches: a recency cache and a frequency cache
self._recency_cache_top = LinkedSet() # paper: T_1
self._recency_cache_bottom = LinkedSet() # paper: B_1
self._frequency_cache_top = LinkedSet() # paper: T_2
self._frequency_cache_bottom = LinkedSet() # paper: B_2
self._maxlen = int(maxlen) # paper: c
if self._maxlen <= 0:
raise ValueError('maxlen must be positive')
# _p is the target number of elements for the recency cache top
# which means that _maxlen - _p is the target number of elements for the frequency cache top
# It is the target number since it will be a real number at some point and not a natural number.
self._p = 0
@inheritdoc(Cache)
def __len__(self):
return self._frequency_cache_top.__len__() + self._recency_cache_top.__len__()
@property
@inheritdoc(Cache)
def maxlen(self):
return self._maxlen
@inheritdoc(Cache)
def dump(self):
top_parts = deepcopy(list(self._frequency_cache_top))
top_parts.extend(list(self._recency_cache_top))
return top_parts
def position(self, k):
"""Return the current position of an item in the cache. Position *0*
refers to the head of the frequency cache (i.e. most recently used item
that was used at least twice) if there is an element in the frequency cache.
This method does not change the internal state of the cache.
Parameters
----------
k : any hashable type
The item looked up in the cache
Returns
-------
position : int
The current position of the item in the cache
"""
if k in self._frequency_cache_top:
return self._frequency_cache_top.index(k)
elif k in self._recency_cache_top:
return self._recency_cache_top.index(k) + self._frequency_cache_top.__len__()
else:
raise ValueError('The item %s is not in the cache' % str(k))
@inheritdoc(Cache)
def has(self, k):
if k in self._frequency_cache_top:
return True
elif k in self._recency_cache_top:
return True
else:
return False
@inheritdoc(Cache)
def get(self, k, weight):
# two basic cases:
# 1. cache hit
# 2. cache miss
if not self.has(k):
# cache miss - do not change state of cache (subsequent put() operation can do that)
return False
else:
# cache hit - change state of cache by moving up k
if k in self._recency_cache_top:
# move k to top of frequency cache
self._recency_cache_top.remove(k)
self._frequency_cache_top.append_top(k)
else: # k is in frequency cache
self._frequency_cache_top.move_to_top(k)
return True
def put(self, k, weight):
"""Register an item's occurrence with the cache if not already inserted.
This operation changes the state of the cache in that it might influence
the number of elements taken from the recency and frequency caches and
possibly replace an element from one of them.
If the element is already present in the cache, it will pushed to the
top of the cache.
Parameters
----------
k : any hashable type
The item to be inserted
weight : int
The weight of the item (not used here)
Returns
-------
evicted : any hashable type
The evicted object or *None* if no contents were evicted.
"""
# in case of k already being cached, move it to the top of the frequency cache
if self.get(k, weight):
return None
# there are three cases:
# 1. k is in bottom of recency cache (i.e. not cached, only observed)
# 2. k is in bottom of frequency cache (i.e. not cached, only observed)
# 3. k is in neither of the caches (i.e. neither cached nor observed)
if k in self._recency_cache_bottom:
rec = self._recency_cache_bottom.__len__()
freq = self._frequency_cache_bottom.__len__()
delta = 1 if rec >= freq else float(freq) / float(rec)
self._p = min(self._p + delta, self._maxlen)
evicted = self._replace(k, self._p)
self._recency_cache_bottom.remove(k)
self._frequency_cache_top.append_top(k)
return evicted
elif k in self._frequency_cache_bottom:
rec = self._recency_cache_bottom.__len__()
freq = self._frequency_cache_bottom.__len__()
delta = 1 if freq >= rec else float(rec) / float(freq)
self._p = max(self._p - delta, 0)
evicted = self._replace(k, self._p)
self._frequency_cache_bottom.remove(k)
self._frequency_cache_top.append_top(k)
return evicted
else:
# there are two subcases:
# A) recency cache has _maxlen elements, i.e. it is full
# B) recency cache is not full yet
# only in some cases an eviction takes place so the default value is set to None
evicted = None
# A) recency cache full
if self._recency_cache_top.__len__() + self._recency_cache_bottom.__len__() == self._maxlen:
if self._recency_cache_top.__len__() < self._maxlen:
# the actual eviction is from the top of the recency or frequency cache
# dropping from the bottom is not an eviction, it is merely the end of observation
self._recency_cache_bottom.pop_bottom()
evicted = self._replace(k, self._p)
else: # bottom of recency cache is empty
evicted = self._recency_cache_top.pop_bottom()
# B) recency cache not full yet
else:
total_observed = self._frequency_cache_top.__len__() + self._frequency_cache_bottom.__len__() + \
self._recency_cache_top.__len__() + self._recency_cache_bottom.__len__()
if total_observed >= self._maxlen:
if total_observed == 2 * self._maxlen:
self._frequency_cache_bottom.pop_bottom()
evicted = self._replace(k, self._p)
else:
# if the number of observed elements is less than the actual cache size, no removals are necessary
pass
self._recency_cache_top.append_top(k)
return evicted
def _replace(self, k, p):
# REPLACE subroutine from paper - to be used internally only
rec_top_len = self._recency_cache_top.__len__()
if rec_top_len > 0 and (rec_top_len > p or (k in self._frequency_cache_bottom and rec_top_len == p)):
evicted = self._recency_cache_top.pop_bottom()
self._recency_cache_bottom.append_top(evicted)
return evicted
else:
evicted = self._frequency_cache_top.pop_bottom()
self._frequency_cache_bottom.append_top(evicted)
return evicted
@inheritdoc(Cache)
def remove(self, k):
if k in self._frequency_cache_top:
self._frequency_cache_top.remove(k)
return True
elif k in self._frequency_cache_bottom:
self._frequency_cache_bottom.remove(k)
return True
elif k in self._recency_cache_top:
self._recency_cache_top.remove(k)
return True
elif k in self._recency_cache_bottom:
self._recency_cache_bottom.remove(k)
return True
else:
return False
@inheritdoc(Cache)
def clear(self):
self._frequency_cache_bottom.clear()
self._frequency_cache_top.clear()
self._recency_cache_bottom.clear()
self._recency_cache_top.clear()
self._p = 0
def get_p(self):
return self._p
def print_internal_dump(self):
print("%s %s %s %s" % (str(self._recency_cache_bottom), str(self._recency_cache_top),
str(self._frequency_cache_bottom), str(self._frequency_cache_top)))