From: David Gudeman To: email@example.com Cc: Philip Oakley Sent: Sunday, June 16, 2013 11:31 PM Subject: Re: [git-users] what is the point of rebase?
Thanks for taking the time for such a detailed reply, Philip, but everything you say seems to be true of merge as well so I still don't get what is special about rebase. Is it just merge+throw away history? And if so, why throw away the history rather than just hide it? On Thursday, June 13, 2013 12:31:07 PM UTC-7, Philip Oakley wrote: From: David Gdeman Sent: Thursday, June 13, 2013 7:12 PM Subject: [git-users] what is the point of rebase? I've been getting to know git recently as part of some work I needed to do, and I love the easy branching and merging, but I have to admit that rebase is confusing me. I'm not confused about what it does (I don't think); I'm confused about what the point is. As far as I can tell, rebase is just the same as doing a merge and then throwing away some history. Why throw away the history? All of the documentation I can find just refers to making history "clean", but the history doesn't have to actually BE clean to LOOK clean. So why? Or here is another way to ask the question. Suppose git repositories had a special flag that you could put on a branch that said, "don't show this branch in histories or push it or allow it to be pulled unless the user does something special to ask for hidden branches". Then suppose git had a merge-and-hide command that would do a merge and then set this flag on the topic branch to effectively hide it unless the user really wants to see it. What does rebase accomplish that merge-and-hide would not? I keep feeling that there must be something else, otherwise why deal with the potential negative consequences of deleting history unrecoverably? All of the documentation on rebase talks about the problem of rebasing a branch out from under someone who is still working on it. So what is the advantage of rebase over merge-and-hide that makes it worth dealing with this problem. Rebase is a way, within a distributed system, of noticing that the world has moved on since you started on your magic topic branch. So you want your magic topic branch to cleanly apply to the New World Order of the upstream repo, hence you 'rebase', or transfer, your series of nice small changes (commits) to the latest upstream reference point (often tip of master/production), and while doing the rebase, you fix all the conflicts (with the NWO changes) as you go to create a clean sequence, and then you will have a commit/patch series that can either be fast forward applied, or merged without conflict. Obviously (?), having done your rebase you will have to style check, compile and test you new magic code to see if it actually works as planned without any regressions (and fix a few minor mistakes). By which time the NWO has moved on again, so another quick rebase gets you to the head of the queue, and you are awarded tea and medals. The other scenario is that you are working on say git itself and you send in patches for review, which end up with fixups and comments, so you have to continue to rebase your own work forward to the relevant start point, especially if there is an overlap with other patch series. The "problem" doesn't exist in other, non-distributed, systems because of the restrictive check-out - check-in process which nails both feet to the floor to stop you going round in circles (and limits progress!). Rebase lets you leap ahead and catch up with the latest and greatest code release, or a collaborators code, or wherever. Philip Hi david, Interesting question. The distinction is about 'who does what', and how is the hsitory to be presented. If it is just you on your own, then a rebase is likely to be rare. You would use it if you started a piece of work from the wrong start point and wanted to make that commit series start from the right point. Otherwise you can merge your way forward anyway you please. In a multi-developer situation there are often rules and conventions that mean you have to 'keep up' with the work of others, so you have to sort out the conflicts *before* your commits are merged into the main workflow (with the merge having minimal conflicts), so you rebase your work, in your local repo, onto the tip of the fetched mainline (which had moved on), fixing the conflicts as the commmits are rebased, leaving you with a clean series that obviously can be either fast forwarded, or merged without conflict, into the main line. Summary. In a rebase you fix conflicts before the merge, while in a regular merge you usually have conflicts to fixup afterwards (after the auto-merge step). Philip -- You received this message because you are subscribed to the Google Groups "Git for human beings" group. To unsubscribe from this group and stop receiving emails from it, send an email to git-users+unsubscr...@googlegroups.com. For more options, visit https://groups.google.com/groups/opt_out.