[webkit-dev] Faster Git SVN updates

[Eric Seidel]

I've now posted a patch to fix update-webkit as well:
https://bugs.webkit.org/show_bug.cgi?id=50273

Once that lands, I'll move the EWS bots over to using this "new" setup.
 Assuming those stay working, we can teach the tools to offer to fix "old"
setups.

-eric

On Mon, Nov 22, 2010 at 4:58 PM, Ojan Vafai <ojan at chromium.org> wrote:

> http://trac.webkit.org/changeset/72575 for having scm.py do the right
> thing.
>
> On Thu, Nov 18, 2010 at 4:11 PM, Eric Seidel <eric at webkit.org> wrote:
>
>> OK.  Sounds we should make this setup default.  I'll see if we can't
>> educate update-webkit and webkitpy/common/checkout/scm.py about detecting
>> this setup and doing the right thing in that case.
>>
>> I'll file a separate bug about making scm.py's Git object use --no-rebase
>> during dcommit.
>>
>> -eric
>>
>>
>> On Thu, Nov 18, 2010 at 4:08 PM, Evan Martin <evan at chromium.org> wrote:
>>
>>> On Thu, Nov 18, 2010 at 3:36 PM, David Levin <levin at google.com> wrote:
>>> >> It's some magical setup by which your git svn fetchs will be much
>>> faser.
>>> >>  But I've heard it's buggy?  Can lead to local repository corruption?
>>> >> Can someone set me straight?
>>>
>>> No magic, just standard git: complicated, but logical once you
>>> understand how it works. :\
>>>
>>> It means that both "git pull" and "git svn fetch" will be updating the
>>> same branch.  When the latter sees the former has pulled down new
>>> stuff (quickly, via the fast git protocol), it knows to rebuild its
>>> metadata from the new stuff you fetched (rather than fetching it all
>>> over again via the slow svn protocol).
>>>
>>> There's a catch: if you "git svn fetch", that creates new commits
>>> locally.  When you later "git pull", you get the commits that were
>>> constructed by git.webkit.org, which don't match (due to differing
>>> timestamps).  This may screw up rebase, but I believe it's smart
>>> enough to recognize the commits are "the same" (applied the same diff;
>>> in git jargon, they have the same patch-id).  In practice you don't
>>> even run "git svn fetch" except when the git server is behind, so I
>>> don't know if there are corner cases here that I haven't run into.  (I
>>> also haven't tried this on Windows in a while -- kind of terrified of
>>> git there, though I hear it works for others.)
>>>
>>> In particular for bots that are not committing, I see no catch, other
>>> than that they will be behind whenever git.webkit.org is behind.
>>>
>>> >> The current git svn fetch is *super* slow.  Especially if you're
>>> behind by
>>> >> more than a day or two.
>>> >> If there was a way to make this faster method safe, by wrapping it in
>>> some
>>> >> other (error-checking) command which knew how to fall back to git svn
>>> >> rebase, etc. when necessary I would love to make it the default method
>>> for
>>> >> all WebKit get users.
>>>
>>> I have instructed all Chrome git users to use this method since
>>> (checking the commit history...) Feb 2009 and it seems to work for us.
>>>  Note that you need git >= 1.6.1 or so for it to work properly.  I
>>> also use this method for working on WebKit (though I've only committed
>>> around 60 patches so I mostly use it for pulling down new code).
>>>
>>> PS: our tools also run svn dcommit with "--no-rebase" to avoid
>>> needlessly going out to svn again after committing.
>>>
>>
>>
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>>
>>
>
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