On 9/25/2018 2:01 PM, Stefan Beller wrote:
On Tue, Sep 25, 2018 at 7:30 AM Derrick Stolee <stolee@xxxxxxxxx> wrote:
On 9/25/2018 3:06 AM, Patrick Steinhardt wrote:
On Mon, Sep 24, 2018 at 11:32:23PM +0200, SZEDER Gábor wrote:
On Mon, Sep 24, 2018 at 02:15:30PM -0700, Derrick Stolee via GitGitGadget wrote:
From: Derrick Stolee <dstolee@xxxxxxxxxxxxx>
The index v4 format has been available since 2012 with 9d22778
"reach-cache.c: write prefix-compressed names in the index". Since
the format has been stable for so long, almost all versions of Git
in use today understand version 4, removing one barrier to upgrade
-- that someone may want to downgrade and needs a working repo.
What about alternative implementations, like JGit, libgit2, etc.?
Speaking of libgit2, we are able to read and write index v4 since
commit c1b370e93
This is a good point, Szeder.
Patrick: I'm glad LibGit2 is up-to-date with index formats.
Unfortunately, taking a look (for the first time) at the JGit code
reveals that they don't appear to have v4 support. In
org.eclipse.jgit/src/org/eclipse/jgit/dircache/DirCache.java, the
DirCache.readFrom() method: lines 488-494, I see the following snippet:
final int ver = NB.decodeInt32(hdr, 4);
boolean extended = false;
if (ver == 3)
extended = true;
else if (ver != 2)
throw new
CorruptObjectException(MessageFormat.format(
JGitText.get().unknownDIRCVersion, Integer.valueOf(ver)));
It looks like this will immediately throw with versions other than 2 or 3.
I'm adding Jonathan Nieder to CC so he can check with JGit people about
the impact of this change.
JGit is used both on the server (which doesn't use index/staging area)
as well as client side as e.g. an Eclipse integration, which would
very much like to use the index.
Adding Matthias Sohn as well, who is active in JGit and cares
more about the client side than Googlers who only make use
of the server side part of JGit.
Stefan
In addition to the compatibility with other implementations of git
question, I think we should include Duy's patch [1] to "optimize reading
index format v4" before flipping the default to V4.
In my testing, this reduced the index load time of V4 by 10%-15% making
the CPU cost only ~2% more expensive than V2 or V3 indexes. This
increase in CPU cost is more than offset by the significant reduction in
file IO due to the reduced index file size.
[1] https://public-inbox.org/git/20180825064458.28484-1-pclouds@xxxxxxxxx/
