On Mon, Mar 07, 2022 at 01:34:57PM -0800, Junio C Hamano wrote: > Derrick Stolee <derrickstolee@xxxxxxxxxx> writes: > > > ... Git does not > > support parallel writers doing significant updates like full > > repacks and GCs and instead relies on the user to control the > > concurrency there. > > At least when we set out to give our users Git, allowing such > concurrent writing without corrupting repositories was what we aimed > to achieve. If you did two simultanenous repacks, one of the may > fail while trying to acquire a lock or two, so from waste-avoidance > perspective, there is a strong incentive on the user's side to make > sure such housecleaning tasks are not triggered needlessly and > simultanously, but it shouldn't lead to repository corruption. It is not true that `git repack` does not support parallel writers. Indeed, `repack` doesn't hold any locks on the repository ahead of time, but the concurrent writers situation will at worst leave us in a state where objects appear twice across multiple packs. So yes, users are incentivized to limit multiple repack processes from stomping on each other and wasting effort, but multiple writers running `git repack` cannot corrupt a repository. Thanks, Taylor
