Junio C Hamano <gitster@xxxxxxxxx> writes: > Jonathan Tan <jonathantanmy@xxxxxxxxxx> writes: > > > Yes - if the bloom filter contained junk data (in our example, created > > using a different hash function on filenames that have characters that > > exceed 0x7f), the bloom filter would report "no, this commit does not > > contain a change in such-and-such path" and then we would skip the > > commit, even if the commit did have a change in that path. > > Just to help my understanding (read: I am not suggesting this as one > of the holes to exploit to help a smooth transition), does the above > mean that, as long as the path we are asking about does not have a > byte with the high-bit set, we would be OK, even if the Bloom filter > were constructed with a bad function and there were other paths that > had such a byte? Ah, thanks for asking. Yes, the false negative I describe above only happens when the path we're querying for contains a character >0x7f (so if there is no byte with the high-bit set, it is still OK). > > I don't have statistics on this, but if the majority of repos have > > only <=0x7f filenames (which seems reasonable to me), this might save > > sufficient work that we can proceed with bumping the version number and > > ignoring old data. > > > >> Better yet, we should be able to reuse existing Bloom filter data for > >> paths that have all characters <=0xff, and only recompute them where > > "ff" -> "7f" I presume? That was my assumption too, but Taylor can clarify.
