mailing list mirror (one of many)
 help / color / mirror / code / Atom feed
From: Jeff King <>
To: Junio C Hamano <>
Cc: Matt McCutchen <>, git <>
Subject: Re: Protecting old temporary objects being reused from concurrent "git gc"?
Date: Wed, 16 Nov 2016 17:04:50 -0800	[thread overview]
Message-ID: <> (raw)
In-Reply-To: <>

On Wed, Nov 16, 2016 at 10:58:30AM -0800, Junio C Hamano wrote:

> Jeff King <> writes:
> > I suspect the issue is that read-tree populates the cache-tree index
> > extension, and then write-tree omits the object write before it even
> > gets to write_sha1_file().
> Wait a minute.  The entries in the index and trees in the cache-tree
> are root of "still in use" traversal for the purpose of pruning,
> which makes the "something like this" patch unnecessary for the real
> index file.
> And for temporary index files that is kept for 6 months, touching
> tree objects that cache-tree references is irrelevant---the blobs
> recorded in the "list of objects" part of the index will go stale,
> which is a lot more problematic.

I think the case that is helped here is somebody who runs "git
write-tree" and expects that the timestamp on those trees is fresh. So
even more a briefly used index, like:

  export GIT_INDEX_FILE=/tmp/foo
  git read-tree ...
  git write-tree

we'd expect that a "git gc" which runs immediately after would see those
trees as recent and avoid pruning them (and transitively, any blobs that
are reachable from the trees). But I don't think that write-tree
actually freshens them (it sees "oh, we already have these; there is
nothing to write").

I could actually see an argument that the read-tree operation should
freshen the blobs themselves (because we know those blobs are now in
active use, and probably shouldn't be pruned), but I am not sure I agree
there. If only because it is weird that an operation which is otherwise
read-only with respect to the repository would modify the object


  reply	other threads:[~2016-11-17  1:04 UTC|newest]

Thread overview: 13+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2016-11-15 14:13 Protecting old temporary objects being reused from concurrent "git gc"? Matt McCutchen
2016-11-15 17:06 ` Jeff King
2016-11-15 17:33   ` Matt McCutchen
2016-11-15 17:40     ` Jeff King
2016-11-15 19:08       ` [PATCH] git-gc.txt: expand discussion of races with other processes Matt McCutchen
2016-11-15 19:12       ` Protecting old temporary objects being reused from concurrent "git gc"? Matt McCutchen
2016-11-15 20:01       ` Junio C Hamano
2016-11-16  8:07         ` Jeff King
2016-11-16 18:18           ` Junio C Hamano
2016-11-16 18:58       ` Junio C Hamano
2016-11-17  1:04         ` Jeff King [this message]
2016-11-17  1:35           ` Re* " Junio C Hamano
2016-11-17  1:43             ` Jeff King

Reply instructions:

You may reply publicly to this message via plain-text email
using any one of the following methods:

* Save the following mbox file, import it into your mail client,
  and reply-to-all from there: mbox

  Avoid top-posting and favor interleaved quoting:

  List information:

* Reply using the --to, --cc, and --in-reply-to
  switches of git-send-email(1):

  git send-email \ \ \ \ \ \

* If your mail client supports setting the In-Reply-To header
  via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line before the message body.
Code repositories for project(s) associated with this public inbox

This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for read-only IMAP folder(s) and NNTP newsgroup(s).