Change the size of the short hash representation
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Hash: SHA1
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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+ mkdir t
+ cd t
+ hg init
+ echo a
+ hg add a
+ hg commit -t test -u test -d '0 0'
+ hg verify
checking changesets
checking manifests
crosschecking files in changesets and manifests
checking files
1 files, 1 changesets, 1 total revisions
+ hg parents
changeset: 0:acb14030fe0a21b60322c440ad2d20cf7685a376
user: test
date: Wed Dec 31 16:00:00 1969
summary: test
+ hg status
+ hg undo
attempting to rollback last transaction
+ hg verify
checking changesets
checking manifests
crosschecking files in changesets and manifests
checking files
0 files, 0 changesets, 0 total revisions
+ hg parents
+ hg status
A a