> On Feb 11, 2015, at 7:23 AM, Richard Hipp <d...@sqlite.org> wrote: > > On 2/11/15, j. van den hoff <veedeeh...@googlemail.com> wrote: >> >> whatever the reason, the netbsd example (a worst case scenario, really) >> would suggest to chose 12 instead of 10 as the future default length >> to avoid collisions these next some hundred years. > > Maybe the default prefix lengths should auto-adjust depending on the > number of artifacts in the repository?
That could work. If you rearrange the square approximation formula from the Wikipedia article to solve for m, then take the base-2 log of that to get bits, then divide by 4 to get bits per nibble (i.e. hex digits), you get: d = log2(n^2 / 2p) / 4 That is to say, it gives you the number of digits d required to achieve a given chance of collision p in a hash set size n. So for my 97,000 hash repo, we need 13 digits to approach p=1e-6. I suggest making the p value configurable, with a reasonable default. 1e-6 sounds good to me. _______________________________________________ fossil-users mailing list fossil-users@lists.fossil-scm.org http://lists.fossil-scm.org:8080/cgi-bin/mailman/listinfo/fossil-users
