Hi Ludo, On Wed, 20 May 2020 at 23:39, Ludovic Courtès wrote: > By default ‘guix pull’ would now error out if the target commit of a > channel is not a descendant of the currently-used commit, according to > the commit graph. There’s an option to bypass that. ‘guix > time-machine’ behavior is unchanged though: it never complains. What is the extra time cost of such check? Well, it depends on the "distance" between the 2 commits and maybe the complexity of the graph -- it it not clear what happen for complex merge -- but say pulling once a month. It is not easy -- nor impossible -- to evaluate such cost at the level of "guix pull". And I failed to evaluate it using 'commit-relation' with "guix repl" -- Segmentation fault with commit c81457a5883ea43950eb2ecdcbb58a5b144bcd11 and 4bdf4182fe080c3409f6ef9b410146b67cfa2595; probably because I did used correctly the API. Well, what will be the timing impact of checking the "fast-fowardness"? All the best, simon