From: Brian Warner Date: Sun, 22 Oct 2006 03:10:04 +0000 (-0700) Subject: tool to generate an overhead/alacrity table for various hashing schemes X-Git-Tag: tahoe_v0.1.0-0-UNSTABLE~554 X-Git-Url: https://git.rkrishnan.org/a?a=commitdiff_plain;h=4968ca98ccfd6732a5344411a2c404cb298c65a6;p=tahoe-lafs%2Ftahoe-lafs.git tool to generate an overhead/alacrity table for various hashing schemes --- 4968ca98ccfd6732a5344411a2c404cb298c65a6 diff --git a/sizes.py b/sizes.py new file mode 100644 index 00000000..cf19b076 --- /dev/null +++ b/sizes.py @@ -0,0 +1,204 @@ +#! /usr/bin/python + +import random, math, os, re +from twisted.python import usage + +class Args(usage.Options): + optParameters = [ + ["mode", "m", "alpha", "validation scheme"], + ["arity", "k", 2, "k (airty) for hash tree"], + ] + def opt_arity(self, option): + self['arity'] = int(option) + def parseArgs(self, *args): + if len(args) > 0: + self['mode'] = args[0] + + +def charttest(): + import gdchart + sizes = [random.randrange(10, 20) for i in range(10)] + x = gdchart.Line() + x.width = 250 + x.height = 250 + x.xtitle = "sample" + x.ytitle = "size" + x.title = "Example Graph" + #x.ext_color = [ "white", "yellow", "red", "blue", "green"] + x.setData(sizes) + #x.setLabels(["Mon", "Tue", "Wed", "Thu", "Fri"]) + x.draw("simple.png") + +KiB=1024 +MiB=1024*KiB +GiB=1024*MiB +TiB=1024*GiB + +class Sizes: + def __init__(self, mode, file_size, arity=2): + MAX_SEGSIZE = 1*MiB + self.mode = mode + self.file_size = file_size + self.seg_size = seg_size = 1.0 * min(MAX_SEGSIZE, file_size) + self.num_segs = num_segs = math.ceil(file_size / seg_size) + self.num_subblocks = num_subblocks = num_segs + + self.num_blocks = num_blocks = 100 + self.blocks_needed = blocks_needed = 25 + + self.subblock_size = subblock_size = seg_size / blocks_needed + self.block_size = block_size = subblock_size * num_subblocks + + # none of this includes the block-level hash chain yet, since that is + # only a function of the number of blocks. All overhead numbers + # assume that the block-level hash chain has already been sent, + # including the root of the subblock-level hash tree. + + if mode == "alpha": + # no hash tree at all + self.subblock_arity = 0 + self.subblock_tree_depth = 0 + self.subblock_overhead = 0 + self.bytes_until_some_data = 20 + block_size + self.block_storage_overhead = 0 + self.block_transmission_overhead = 0 + + elif mode == "beta": + # k=num_subblocks, d=1 + # each subblock has a 20-byte hash + self.subblock_arity = num_subblocks + self.subblock_tree_depth = 1 + self.subblock_overhead = 20 + # the block has a list of hashes, one for each subblock + self.block_storage_overhead = (self.subblock_overhead * + num_subblocks) + # we can get away with not sending the hash of the block that + # we're sending in full, once + self.block_transmission_overhead = self.block_storage_overhead - 20 + # we must get the whole list (so it can be validated) before + # any data can be validated + self.bytes_until_some_data = (self.block_transmission_overhead + + subblock_size) + + elif mode == "gamma": + self.subblock_arity = k = arity + d = math.ceil(math.log(num_subblocks, k)) + self.subblock_tree_depth = d + num_leaves = k ** d + # to make things easier, we make the pessimistic assumption that + # we have to store hashes for all the empty places in the tree + # (when the number of blocks is not an exact exponent of k) + self.subblock_overhead = 20 + # the subblock hashes are organized into a k-ary tree, which + # means storing (and eventually transmitting) more hashes. This + # count includes all the low-level block hashes and the root. + hash_nodes = (num_leaves*k - 1) / (k - 1) + #print "hash_depth", d + #print "num_leaves", num_leaves + #print "hash_nodes", hash_nodes + # the storage overhead is this + self.block_storage_overhead = 20 * (hash_nodes - 1) + # the transmission overhead is smaller: if we actually transmit + # every subblock, we don't have to transmit 1/k of the + # lowest-level subblock hashes, and we don't have to transmit the + # root because it was already sent with the block-level hash tree + self.block_transmission_overhead = 20 * (hash_nodes + - 1 # the root + - num_leaves / k) + # we must get a full sibling hash chain before we can validate + # any data + sibling_length = d * (k-1) + self.bytes_until_some_data = 20 * sibling_length + subblock_size + + + + else: + raise RuntimeError("unknown mode '%s" % mode) + + self.storage_overhead = self.block_storage_overhead * num_blocks + self.storage_overhead_percentage = 100.0 * self.storage_overhead / file_size + + def dump(self): + for k in ("mode", "file_size", "seg_size", + "num_segs", "num_subblocks", "num_blocks", "blocks_needed", + "subblock_size", "block_size", + "subblock_arity", "subblock_tree_depth", + "subblock_overhead", + "block_storage_overhead", "block_transmission_overhead", + "storage_overhead", "storage_overhead_percentage", + "bytes_until_some_data"): + print k, getattr(self, k) + +def fmt(num, trim=False): + if num < KiB: + s = str(num) + "#" + elif num < MiB: + s = "%.2fk" % (num / KiB) + elif num < GiB: + s = "%.2fM" % (num / MiB) + elif num < TiB: + s = "%.2fG" % (num / GiB) + else: + s = "big" + if trim: + s = re.sub(r'(\.0+)([kMG#])', + lambda m: m.group(2), + s) + else: + s = re.sub(r'(\.0+)([kMG#])', + lambda m: (" "*len(m.group(1))+m.group(2)), + s) + if s.endswith("#"): + s = s[:-1] + " " + return s + +def text(): + opts = Args() + opts.parseOptions() + mode = opts["mode"] + arity = opts["arity"] + # 0123456789012345678901234567890123456789012345678901234567890123456 + print "mode=%s" % mode, " arity=%d" % arity + print " storage storage" + print "Size blocksize overhead overhead k d alacrity" + print " (bytes) (%)" + print "------- ------- -------- -------- ---- -- --------" + sizes = [2 ** i for i in range(7, 32)] + for file_size in sizes: + s = Sizes(mode, file_size, arity) + out = "" + out += "%7s " % fmt(file_size, trim=True) + out += "%7s " % fmt(s.block_size) + out += "%8s" % fmt(s.storage_overhead) + out += "%10.2f " % s.storage_overhead_percentage + out += " %4d" % int(s.subblock_arity) + out += " %2d" % int(s.subblock_tree_depth) + out += " %8s" % fmt(s.bytes_until_some_data) + print out + + +def graph(): + # doesn't work yet + import Gnuplot + opts = Args() + opts.parseOptions() + mode = opts["mode"] + arity = opts["arity"] + g = Gnuplot.Gnuplot(debug=1) + g.title("overhead / alacrity tradeoffs") + g.xlabel("file size") + g.ylabel("stuff") + sizes = [2 ** i for i in range(7, 32)] + series = {"overhead": {}, "alacrity": {}} + for file_size in sizes: + s = Sizes(mode, file_size, arity) + series["overhead"][file_size] = s.storage_overhead_percentage + series["alacrity"][file_size] = s.bytes_until_some_data + g.plot([ (fs, series["overhead"][fs]) + for fs in sizes ]) + raw_input("press return") + + +if __name__ == '__main__': + text() + #graph()