stable version 1 that made an index only when a flush was constructed at
https://lists.cpunks.org/pipermail/cypherpunks/2022-July/102291.html
attached wip version is behaving consistently and retains a running index
updated every write, but makes less optimized trees because i have not
implemented branch merging or making branches shallower when they get
skinnier, and am using recursion and excessive heap construction to shorten
the implementation for my confused mind.
I seem to have more inhibition when I try to make dependecy components with
suites of methods. very hard to reuse these. so I redid it a different way.
Just implemented write merging.
from collections import namedtuple
import bisect
class Chunk:
def __init__(self, start, end, data, height=0, leaf_count=1, age=0):
self.start = start
self.end = end
self.data = data
self.height = height
self.leaf_count = leaf_count
self.age = age
def __len__(self):
return self.end - self.start
#
#class ChunkSlice:
# def __init__(self, chunk, start, end):
# super().__init__(start, end)
# self.chunk = chunk
class Flush(Chunk):
class Entry(Chunk):
def __init__(self, start, end, chunk):
super().__init__(start, end, chunk, height=0, leaf_count=1, age=chunk.age)
if type(chunk) is Flush:
self.leaf_count = 0
self.height = 0
for entry in self.flush_entries():
self.leaf_count += entry.leaf_count
self.height = max(self.height, entry.height + 1)
def flush_entries(self):
assert type(self.data) is Flush
return (
Flush.Entry(max(entry.start, self.start), min(entry.end, self.end), entry.data)
for entry in self.data.data
if entry.start < self.end and entry.end > self.start
)
def chunk_data(self):
assert type(self.data) is Chunk
return self.data.data[self.start - self.data.start : self.end - self.data.start]
def __init__(self, prev_flush = None):
if prev_flush is not None:
leaf_count = prev_flush.leaf_count
max_height = prev_flush.leaf_count.bit_length()
super().__init__(prev_flush.start, prev_flush.end, [], leaf_count=0, age=prev_flush.age+1)
self.add(prev_flush)
for entry in prev_flush.data:
if entry.height >= max_height:
#while type(entry.data) is Flush:
# # reduce depth when only one subentry is used
# count = 0
# for subentry in entry:
# count += 1
# if count > 1:
# break
# if count <= 1:
# entry = subentry
# else:
# break
self.add(entry)
else:
super().__init__(None, None, [], height=1, leaf_count=0)
def add(self, *adjacents):
adjacents = [
adjacent if type(adjacent) is Flush.Entry
else Flush.Entry(adjacent.start, adjacent.end, adjacent)
for adjacent in adjacents
]
if self.start is None:
self.start = adjacents[0].start
self.end = adjacents[-1].end
else:
self.start = min(self.start, adjacents[0].start)
self.end = max(self.end, adjacents[-1].end)
# first idx with end >= start
start_idx = bisect.bisect_left([entry.end for entry in self.data], adjacents[0].start)
# first idx with start > end
end_idx = bisect.bisect_right([entry.start for entry in self.data], adjacents[-1].end, start_idx)
replaced = self.data[start_idx:end_idx]
if len(replaced):
if replaced[0].start < adjacents[0].start:
adjacents = [
Flush.Entry(
replaced[0].start, adjacents[0].start, replaced[0].data
),
*adjacents
]
if replaced[-1].end > adjacents[-1].end:
adjacents = [
*adjacents,
Flush.Entry(
adjacents[-1].end, replaced[-1].end, replaced[-1].data
)
]
for idx, (left_adjacent, right_adjacent) in reversed([*enumerate(zip(adjacents[:-1], adjacents[1:]))]):
# merge writes
if (
type(left_adjacent.data) is Chunk and
type(right_adjacent.data) is Chunk and
left_adjacent.age == self.age and
right_adjacent.age == self.age and
left_adjacent.end == right_adjacent.start
):
left_adjacent.data = Chunk(
left_adjacent.start,
right_adjacent.end,
left_adjacent.chunk_data() + right_adjacent.chunk_data()
)
left_adjacent.end = right_adjacent.end
adjacents.pop(idx+1)
self.leaf_count += sum((adjacent.leaf_count for adjacent in adjacents))
self.leaf_count -= sum((old.leaf_count for old in replaced))
self.data[start_idx:end_idx] = adjacents
self.height = max((entry.height for entry in self.data)) + 1
#self.check_leaf_count(self.start, self.end)
def write(self, offset, data):
chunk = Chunk(offset, offset + len(data), data, age=self.age)
return self.add(chunk)
def read(self, start, max_end = float('inf')):
# first idx with end > start
idx = bisect.bisect_right([entry.end for entry in self.data], start)
if idx == len(self.data):
return bytes(4096)
entry = self.data[idx]
if entry.start > start:
end = min(max_end, entry.start)
return bytes(end - start)
end = min(max_end, entry.end)
if type(entry.data) is Flush:
return entry.data.read(start, end)
elif type(entry.data) is Chunk:
datastart = start - entry.data.start
dataend = end - entry.data.start
return entry.data.data[datastart : dataend]
#def check_leaf_count(self, start, end):
# leaf_count = 0
# wrapper = Flush.Entry(start, end, self)
# for entry in wrapper.flush_entries():
# if type(entry.data) is Flush:
# entry_leaf_count = entry.data.check_leaf_count(entry.start, entry.end)
# assert entry_leaf_count == entry.leaf_count
# leaf_count += entry_leaf_count
# else:
# leaf_count += entry.data.leaf_count
# assert leaf_count == wrapper.leaf_count
# if start == self.start and end == self.end:
# assert leaf_count == self.leaf_count
# return leaf_count
if __name__ == '__main__':
import random
random.seed(2)
SIZE=4096
comparison = bytearray(SIZE)
store = Flush()
def compare(store, comparison):
offset = 0
while offset < len(comparison):
data = store.read(offset)[:len(comparison) - offset]
assert data == comparison[offset:offset+len(data)]
offset += len(data)
#store.check_leaf_count(store.start, store.end)
return True
for flushes in range(1024):
for writes in range(random.randint(1,16)):
start = random.randint(0, SIZE)
end = random.randint(0, SIZE)
if end < start:
start, end = end, start
end = (end + start) // 2
size = end - start
data = random.randint(0, (1<<(size*8))-1).to_bytes(size, 'little')
store.write(start, data)
comparison[start:end] = data
#compare(store, comparison)
#print('OK', flushes, writes)#, offset)
compare(store, comparison)
print('OK', len(store.data), 'x', store.height, 'count =', store.leaf_count, 'flushes =', flushes)#, writes)#, offset)
store = Flush(prev_flush = store)
compare(store, comparison)
