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https://github.com/tahoe-lafs/tahoe-lafs.git
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85 lines
2.9 KiB
Python
85 lines
2.9 KiB
Python
#!/usr/bin/env python
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import sys, math
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from allmydata import upload, uri, encode, storage
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from allmydata.util import mathutil
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def roundup(size, blocksize=4096):
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return blocksize * mathutil.div_ceil(size, blocksize)
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class BigFakeString:
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def __init__(self, length):
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self.length = length
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self.fp = 0
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def seek(self, offset, whence=0):
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if whence == 0:
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self.fp = offset
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elif whence == 1:
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self.fp += offset
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elif whence == 2:
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self.fp = self.length - offset
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def tell(self):
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return self.fp
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def calc(filesize, params=(3,7,10), segsize=encode.Encoder.MAX_SEGMENT_SIZE):
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num_shares = params[2]
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if filesize <= upload.Uploader.URI_LIT_SIZE_THRESHOLD:
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urisize = len(uri.pack_lit("A"*filesize))
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sharesize = 0
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sharespace = 0
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else:
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u = upload.FileUploader(None)
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u.set_params(params)
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# unfortunately, Encoder doesn't currently lend itself to answering
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# this question without measuring a filesize, so we have to give it a
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# fake one
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data = BigFakeString(filesize)
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u.set_filehandle(data)
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u.set_encryption_key("a"*16)
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sharesize, blocksize = u.setup_encoder()
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# how much overhead?
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# 0x20 bytes of offsets
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# 0x04 bytes of extension length
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# 0x1ad bytes of extension (=429)
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# total is 465 bytes
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num_segments = mathutil.div_ceil(filesize, segsize)
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num_share_hashes = int(math.log(mathutil.next_power_of_k(num_shares, 2),
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2)) + 1
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sharesize = storage.allocated_size(sharesize, num_segments,
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num_share_hashes,
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429)
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sharespace = num_shares * roundup(sharesize)
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urisize = len(uri.pack_uri(storage_index="a"*32,
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key="a"*16,
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uri_extension_hash="a"*32,
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needed_shares=params[0],
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total_shares=params[2],
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size=filesize))
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return urisize, sharesize, sharespace
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def main():
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filesize = int(sys.argv[1])
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urisize, sharesize, sharespace = calc(filesize)
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print "urisize:", urisize
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print "sharesize: %10d" % sharesize
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print "sharespace: %10d" % sharespace
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print "desired expansion: %1.1f" % (1.0 * 10 / 3)
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print "effective expansion: %1.1f" % (1.0 * sharespace / filesize)
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def chart():
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filesize = 2
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while filesize < 2**20:
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urisize, sharesize, sharespace = calc(int(filesize))
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expansion = 1.0 * sharespace / int(filesize)
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print "%d,%d,%d,%1.2f" % (int(filesize), urisize, sharespace, expansion)
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filesize = filesize * 2**0.5
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if __name__ == '__main__':
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if sys.argv[1] == "chart":
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chart()
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else:
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main()
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