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Re: Log-addressing branch ready for review

From: Stefan Fuhrmann <stefan.fuhrmann_at_wandisco.com>
Date: Mon, 2 Dec 2013 09:59:26 +0100

On Wed, Nov 27, 2013 at 6:55 PM, Julian Foad <julianfoad_at_btopenworld.com>wrote:

> Stefan Fuhrmann wrote:
> >>>>> As of r1516665, work on this branch has been completed.
> >>>>> Please review. See the BRANCH-README for the list of
> >>>>> major changes.
>
> I have not reviewed, but looked at how to review it.
>
> First I am looking for an overall description of the changes. The
> BRANCH-README says:
>
> [[[
> This is an integration / development branch to copy / implement and
> review the logical addressing feature originally developed on the
> fsfs-format7 branch. After review and after the fsfs-improvements
> branch got merged into /trunk, this whole branch will get merged
> into /trunk as well.
>
> Features to implement here:
>
> * support for logical addressing
> * switch to format 7; use log addressing after for new shards created
> after svnadmin upgrade
> * block read / data prefetch for f7 rev / pack file data
> * reorder data upon pack
> * add checksums to index data
> * improve verification to cover all f7 rev / pack file data
>
> More on this here:
> http://svn.haxx.se/dev/archive-2013-06/0755.shtml
> http://svn.haxx.se/dev/archive-2013-07/0059.shtml
> ]]]
>
> I don't know how up to date that is, but anyhow it doesn't precisely
> describe the changes.

I only used it as a TODO list.

> If you could perhaps, starting from this text, turn it into the standard
> log message format that you would eventually include in the merge log
> message, that would be much better. I am in favour of merges having a log
> message that really describes what's being merged, since trying to
> understand it from scanning the original series of branch commits can be
> very inefficient.
>

r1546928 on the fsfs-improvements branch now contains a
summary of all f7 changes. It does not give function-level
detail but describes the intended changes on a per-file level.

> Then, to see the actual changes, we can run a diff if we first discover
> the trunk revision to diff against:

> $ svn mergeinfo ^/subversion/trunk \
> ^/subversion/branches/fsfs-improvements
> youngest common ancestor
> | last full merge
> | | tip of branch
> | | | repository path
>
> 1499980 1545953 1546120
> | | |
> -------| |------------ subversion/trunk
> \ \
> \ \
> --| |------------ subversion/branches/fsfs-improvements
> |
> 1546120
>
> $ svn mergeinfo ^/subversion/branches/fsfs-improvements \
> ^/subversion/branches/log-addressing
> youngest common ancestor
> | last full merge
> | | tip of branch
> | | | repository path
>
> 1509278 1545955 1546118
> | | |
> -------| |------------ subversion/branches/fsfs-improvements
> \ \
> \ \
> --| |------------ subversion/branches/log-addressing
> |
> 1546118
>
> $ svn diff --old=^/subversion/trunk_at_1545953 \
> --new=^/subversion/branches/log-addressing > d
>
> I find it easier to have the changes in a trunk WC and use diff-aware
> editors than to browse the patch file directly. I can apply this patch:
>
> $ svn patch d
> D subversion/libsvn_subr/md5.h
> D subversion/libsvn_subr/sha1.c
> D subversion/libsvn_subr/sha1.h
> U build.conf
> A BRANCH-README
> U subversion/libsvn_fs_base/fs.c
> [...]
>
> OK, fine. (I got a minor text conflict in a test, presumably due to a
> recent trunk change that's not yet sync'd to the branch.)
>
> Alternatively, I usually just run the proposed merge. At first I tried to
> merge it directly to a trunk WC, using automatic merge: "svn merge
> ^/subversion/branches/log-addressing". No go. Major conflicts.
>
> The branching structure is like this (showing only the most recent merges):
>
> ------------------------ trunk
> \ ... \
> +-----------+------- branches/fsfs-improvements
> \ ... \
> +-----------+--- branches/log-addressing
>
> Subversion's automatic merge doesn't support tracking merges going round a
> cycle (trunk -> fsfs-imp. -> log-addr. -> trunk). That's the basic reason
> it produces conflicts when we try. The "proper" way to merge this back to
> trunk, in terms of what Subversion's automatic merge supports, is first to
> merge it to fsfs-improvements. That works fine in my trial. (I only ran the
> merge, didn't try to build the resulting code.) Then I suppose a merge from
> fsfs-improvements to trunk would work fine.
>

Yes, that is a limitation in the way we currently use merge
tracking: Catch-up merges must follow the branch hierarchy.

Cherry-picks are slightly less critical since one would expect
them to cause (trivial) conflicts anyways when resync'ing
the source branch with the target.

It looks like fsfs-improvements itself currently has no changes on it that
> have not been merged to trunk (apart from BRANCH-README and a mergeinfo
> property).
>
> Stefan, does all this match your understanding? Would it make sense for
> you to merge this to fsfs-improvements right away, to make it easier for
> other people to run a trial merge to trunk? And then of course the proposal
> would be to merge fsfs-improvements to trunk, rather than log-addressing to
> trunk. (I'm assuming this is the only active sub-branch off the
> fsfs-improvements branch at the moment.)
>

That is correct. I just merged everything into fsfs-improvements
and dropped the sub-branch.

-- Stefan^2.
Received on 2013-12-02 10:00:05 CET

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