Change the size of the short hash representation
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Change the size of the short hash representation
First note that this number doesn't really matter, as we always check
for ambiguous short hash ids.
Here's the math on collision probability:
>>> import math
>>> def p(f, n): return 1 - (1 / math.exp(n**2/(2*f)))
...
>>> p(2**32, 30000.0)
0.
09947179164613551 # with 30000 changesets (BKCVS), we have a 9% chance
>>> p(2**32, 65000.0)
0.
38850881217977273 # and with a full import from BK, we'd have a 39% chance
>>> p(2**40, 1e6)
0.
36539171908447321 # we'd like to be "safe" for 1M csets, so 40 isn't enough
>>> p(2**48, 1e6)
0.
001774780051374103 # But 48 looks good
>>> p(2**48, 1e7)
0.
16275260939624481
>>> p(2**48, 5e6)
0.
043437281083569146
>>> p(2**48, 2e6)
0.
0070802434913129764
>>> p(2**48, 3e6)
0.
01586009440574343
manifest hash:
24d9f928a463f46708b0e11fb781d5a241851424
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=CNWk
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#!/bin/bash
set -ex
mkdir test
cd test
echo foo>foo
hg init
hg addremove
hg commit -t "1"
hg verify
cd ..
mkdir branch
cd branch
hg init ../test
hg co
echo bar>>foo
hg commit -t "2"
cd ../test
hg pull ../branch
hg verify
hg co
cat foo
hg manifest