[Monotone-devel] Re: results of mercurial user survey

[Bruce Stephens]

"Justin Patrin" <address@hidden> writes:

[...]

> Doing a pull and waiting for hours while their machine computes SHA
> hashes is a very large up-front cost to pay for being able to try
> out some new code and a new SCM.

OK, here's some back of the envelope costs.  "openssl speed" says it
can do 632761 64 byte SHA1's per second, 194433 1K per second.  The
current repository contains 6084 revisions, so double that (for a
revision and a roster) and call it 20000.  

Roughly 25000 files and certs to check, so a grand total of 70000
things that need to be SHA1ed.  So the actual SHA1 cost looks not
significant.

I'd guess reconstructing the bytes to check (applying the xdelta
patches and things) is vastly more costly.

RSA verification also seems not too bad: openssl says it can do about
7000 verifies of 1024 bit keys per second, so for 25000 certs that's
less than 10s.  Maybe more (maybe the openssl speed test uses just one
key or something, which might end up in a cache), but it doesn't seem
worth worrying about, IMHO.

(My gut feeling is that storing the text of files (the bulk of the
data) in files rather than in the database ought to be a
win---something like hg.  That should make fiddling with the database
faster, and ought to make looking at the texts faster.  On the other
hand, Graydon didn't find it a win, so it's quite possible I'm wrong.)

[...]