On 3/8/2023 10:55 AM, Taylor Blau wrote: > On Tue, Mar 07, 2023 at 09:52:19AM -0500, Derrick Stolee wrote: >> The prepare_alt_odb() call only _adds_ to the linked odb list. It >> will not remove any existing ODBs. Adding this reprepare_*() method >> makes it such that we can use the union of the alternates available >> across the lifetime of the process. > > Right, that matches my understanding. What I am asking is: since we only > add ODBs to the list, what happens if we can no longer access an > *existing* alternate at the time we call reprepare_alt_odb()? > > It's clear that that now-inaccessible alternate remains in our list of > alternate ODBs, but do all object lookups hitting that ODB fail-over to > the new ODB? I believe so, but it isn't totally clear to me. It's the same as the pack-file list: if we fail to load something from one, then we continue to the next one. If an alternate dir is completely removed during the process, then looking for pack- files again will fail to see any and continue without error. This is already possible by deleting an alternate directory while a Git process is running and might try to open files in it. Git already recovers from this scenario. If you're instead talking about the .git/objects/info/alternates file being modified to remove an alternate from the list, then Git's current behavior is to keep that alternate around for the life of the process, and I recommend continuing that behavior. There's nothing special that we are adding here that doesn't already exist as protections when files are removed beneath the Git process. Thanks, -Stolee
