git-annex/doc/bugs/copy_doesn__39__t_scale.mdwn
Joey Hess c3fbe07d7a do a cleanup commit after moving data from or to a git remote
Added Annex.cleanup, which is a general purpose interface for adding
actions to run at the end.

Remotes with the old git-annex-shell will commit every time, and have no
commit command, so hide stderr when running the commit command.
2012-02-25 18:02:49 -04:00

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Markdown

It seems that git-annex copies every individual file in a separate
transaction. This is quite costly for mass transfers: each file involves a
separate rsync invocation and the creation of a new commit. Even with a
meager thousand files or so in the annex, I have to wait for fifteen
minutes to copy the contents to another disk, simply because every
individual file involves some disk thrashing. Also, it seems suspicious
that the git-annex branch would get a thousands commits of history from the
simple procedure of copying everything to a new repository. Surely it would
be better to first copy everything and then create only a single commit
that registers the changes to the files' availability?
> git-annex is very careful to commit as infrequently as possible,
> and the current version makes *1* commit after all the copies are
> complete, even if it transferred a billion files. The only overhead
> incurred for each file is writing a journal file.
> You must have an old version.
> --[[Joey]]
(I'm also not quite clear on why rsync is being used when both repositories
are local. It seems to be just overhead.)
> Even when copying to another disk it's often on
> some slow bus, and the file is by definition large. So it's
> nice to support resumes of interrupted transfers of files.
> Also because rsync has a handy progress display that is hard to get with cp.
>
> (However, if the copy is to another directory in the same disk, it does
> use cp, and even supports really fast copies on COW filesystems.)
> --[[Joey]]
---
Oneshot mode is now implemented, making git-annex-shell and other
short lifetime processes not bother with committing changes.
[[done]] --[[Joey]]
Update: Now it makes one commit at the very end of such a mass transfer.
--[[Joey]]