On Mon, Jul 29 2019, Jeff King wrote: > On Thu, Jul 25, 2019 at 07:18:57PM -0700, Gregory Szorc wrote: > >> I think I've found some undesirable behavior with regards to the >> behavior of `git gc --auto`. The tl;dr is that a warning message written >> to gc.log can result in `git gc --auto` effectively disabling itself for >> gc.logExpiry. The problem is easier to trigger in 2.22 as a result of >> enabling bitmap indices for bare repositories by default and the >> behavior can easily result in performance degradation, especially on >> servers. > > Yuck, thanks for reporting this. > > As you note, this is a special case of a much larger problem. The other > common case is the "oops, you still have a lot of loose objects after > repacking" warning. There's more discussion and some patches here: > > https://public-inbox.org/git/20180716172717.237373-1-jonathantanmy@xxxxxxxxxx/ > > though I don't think any of the work that came out of that fundamentally > solves the issue. To add to that Gregory probably finds these two old reports of mine interesting. The former is pretty much his report (but for a different root cause, the loose object issue): https://public-inbox.org/git/87inc89j38.fsf@xxxxxxxxxxxxxxxxxxx/ & https://public-inbox.org/git/87fu6bmr0j.fsf@xxxxxxxxxxxxxxxxxxx/ >> I don't prescribe to know the best way to solve this problem. I just >> know it is a footgun sitting in the default Git configuration. And the >> footgun became a lot easier to fire with the introduction of warning >> messages related to bitmap indices and again when bitmap indices were >> enabled by default for bare repositories in Git 2.22. > > IMHO one way to mitigate this is to simply warn less. In particular, if > we are auto-enabling bitmaps, then it doesn't necessarily make sense for > us to warn about them being disabled. > > In the case of .keep files, we've already got 7328482253 (repack: > disable bitmaps-by-default if .keep files exist, 2019-06-29), which > should be in the next released version of Git. But I suspect that's > racy with respect to somebody creating .keep files, and as you note > there are other config options that might prevent us from generating > bitmaps. > > Instead, it may make sense to turn the --write-bitmap-index option of > pack-objects into a tri-state: true/false/auto. Then pack-objects would > know that we are in best-effort mode, and would avoid warning in that > case. That would also let git-repack express its intentions better to > git-pack-objects, so we could replace 7328482253, and keep more of the > logic in pack-objects, which is ultimately what has to make the decision > about whether it can generate bitmaps. Sounds like pentastate to me :) (penta = 5, had to look it up). I.e. in most cases of "auto" we pick a true/false at the outset, whereas this is true/true-but-dont-care-much/false/false-but-dont-care-much with "auto" picking the "-but-dont-care-much" versions of a "soft" true/false. On this general topic a *soft* poke about relying to https://public-inbox.org/git/8736lnxlig.fsf@xxxxxxxxxxxxxxxxxxx/ if you have time. I think a "loose pack" might be a way forward for the loose object proliferation, but maybe I'm wrong. More generally we're really straining the gc.log pass-along-a-message facility.
