On Sun, Mar 05, 2017 at 12:08:45PM +0900, Byungchul Park wrote: > On Fri, Mar 03, 2017 at 09:14:16AM +0100, Peter Zijlstra wrote:
> > > > Now the problem with the above condition is that it makes reports > > harder to decipher, because by avoiding adding redundant links to our > > graph we loose a possible shorter path. > > Let's see the following example: > > A -> B -> C > > where A, B and C are typical lock class. > > Assume the graph above was built and operations happena in the > following order: > > CONTEXT X CONTEXT Y > --------- --------- > acquire DX > acquire A > acquire B > acquire C > > release and commit DX > > where A, B and C are typical lock class, DX is a crosslock class. > > The graph will grow as following _without_ prev_gen_id. > > -> A -> B -> C > / / / > DX ----------- > > where A, B and C are typical lock class, DX is a crosslock class. > > The graph will grow as following _with_ prev_gen_id. > > DX -> A -> B -> C > > where A, B and C are typical lock class, DX is a crosslock class. > > You said the former is better because it has smaller cost in bfs. No, I said the former is better because when you report a DX inversion against C, A and B are not required and the report is easier to understand by _humans_. I don't particularly care about the BFS cost itself. > But it has to use _much_ more memory to keep additional nodes in > graph. Without exaggeration, every crosslock would get linked with all > locks in history locks, on commit, unless redundant. It might be > pretty more than we expect - I will check and let you know how many it > is. Is it still good? Dunno, probably not.. but it would be good to have numbers.
