"Derrick Stolee via GitGitGadget" <[email protected]> writes:
> As I was testing the release candidate, I stumbled across a regression in > 'git merge-base' as a result of the switch to generation numbers. The commit > message in [PATCH 1/1] describes the topology involved, but you can test it > yourself by comparing 'git merge-base v4.8 v4.9' in the Linux kernel. The > regression does not show up when running merge-base for tags at least v4.9, > which is why I didn't see it when I was testing earlier. Strange that it happens; I'll take a look. > The solution is simple, but also will conflict with ds/reachable in next. I > can send a similar patch that applies the same diff into commit-reach.c. > > With the integration of generation numbers into most commit walks coming to > a close [1], it will be time to re-investigate other options for > reachability indexes [2]. As I was digging into the issue with this > regression, I discovered a way we can modify our generation numbers and pair > them with commit dates to give us a simple-to-compute, immutable > two-dimensional reachability index that would be immune to this regression. > I will investigate that more and report back, but it is more important to > fix this regression now. I am interested in what you have created, especially because commit creation dates are imperfect indicators because of clock skew etc. > > Thanks, -Stolee > > [1] https://public-inbox.org/git/[email protected]/[PATCH > 0/6] Use generation numbers for --topo-order > > [2] https://public-inbox.org/git/[email protected]/[RFC] Other chunks > for commit-graph, part 2 - reachability indexes Since then I have found few more possible approaches: - working with repository metagraph[1], where all chains of commits were replaced by edge, perhaps together with DAG Reduction[2] boosting framework on this metagraph - using FELINE-like index (the Graph+Label approch, also known as online search), and for those where this index have false results, use Labels only approach[3] [1] Xian Tang et. al., "An Optimized Labeling Scheme for Reachability Queries", CMC, vol.55, no.2, pp.267-283, 2018 [2] Marco Biazzini, Martin Monperrus, Benoit Baudry "On Analyzing the Topology of Commit Histories in Decentralized Version Control Systems", ICSME 2014 (conference paper) [3] Junfeng Zhou et. al., "Accelerating reachability query processing based on DAG reduction", The VLDB Journal (2018) 27: 271 -- Jakub Narębski
