# Funny repack behaviour

3 messages from 2006-04-08 to 2006-04-08. Participants: Johannes Schindelin, Nicolas Pitre.
Thread: https://gitlist.dev/t/3830

## Johannes Schindelin, 2006-04-08 10:41

Subject: Funny repack behaviour
Message-ID: <Pine.LNX.4.63.0604081233170.3283@wbgn013.biozentrum.uni-wuerzburg.de>
URL: https://gitlist.dev/e/Pine.LNX.4.63.0604081233170.3283%40wbgn013.biozentrum.uni-wuerzburg.de

```
Hi,

I just accidentally reran "git-repack -a -d" on a repository, where I just 
had run it. And I noticed a funny thing: Of about 4000 objects, it reused 
all but 8. So I reran it, and it reused all but 2. I ran it once again, 
and it reused all.

The really funny thing is: it created the same pack every time!

It is not critical, evidently, but I'd like to know what is causing this 
rather undeterministic behaviour. (Before you ask: no, I did not make a 
backup before running the tests, so I unfortunately cannot reproduce it).

Ciao,
Dscho

P.S.: This is the output:

$ git-repack -a -d
Generating pack...
Done counting 4259 objects.
Deltifying 4259 objects.
 100% (4259/4259) done
Writing 4259 objects.
 100% (4259/4259) done
Total 4259, written 4259 (delta 3391), reused 4241 (delta 3379)
Pack pack-66bd976bbdc2ac6da623b8af02037218ecd72ef0 created.
$ git-repack -a -d
Generating pack...
Done counting 4259 objects.
Deltifying 4259 objects.
 100% (4259/4259) done
Writing 4259 objects.
 100% (4259/4259) done
Total 4259, written 4259 (delta 3393), reused 4257 (delta 3391)
Pack pack-66bd976bbdc2ac6da623b8af02037218ecd72ef0 created.
$ git-repack -a -d
Generating pack...
Done counting 4259 objects.
Deltifying 4259 objects.
 100% (4259/4259) done
Writing 4259 objects.
 100% (4259/4259) done
Total 4259, written 4259 (delta 3393), reused 4259 (delta 3393)
Pack pack-66bd976bbdc2ac6da623b8af02037218ecd72ef0 created.

```

## Nicolas Pitre, 2006-04-08 19:44

Subject: Re: Funny repack behaviour
Message-ID: <Pine.LNX.4.64.0604081528070.2215@localhost.localdomain>
URL: https://gitlist.dev/e/Pine.LNX.4.64.0604081528070.2215%40localhost.localdomain
In-Reply-To: <Pine.LNX.4.63.0604081233170.3283@wbgn013.biozentrum.uni-wuerzburg.de>

```
On Sat, 8 Apr 2006, Johannes Schindelin wrote:

> Hi,
> 
> I just accidentally reran "git-repack -a -d" on a repository, where I just 
> had run it. And I noticed a funny thing: Of about 4000 objects, it reused 
> all but 8. So I reran it, and it reused all but 2. I ran it once again, 
> and it reused all.
> 
> The really funny thing is: it created the same pack every time!

Probably not.  Subsequent packs were most probably even smaller !

> It is not critical, evidently, but I'd like to know what is causing this 
> rather undeterministic behaviour. (Before you ask: no, I did not make a 
> backup before running the tests, so I unfortunately cannot reproduce it).

To reproduce, or rather to reset the pack state, just use
"git-repack -a -f -d" then  "git-repack -a -d" multiple times again.

For example, on the current git archive:

$ git-repack -a -f -d
[...]
Total 16548, written 16548 (delta 11007), reused 5390 (delta 0)
Pack pack-af9d39abfcb5fd6fd554f7fc8d1704f8dd2329e0 created.

pack size = 6032083 bytes.

$ git-repack -a -d
[...]
Total 16548, written 16548 (delta 11030), reused 16525 (delta 11007)
Pack pack-af9d39abfcb5fd6fd554f7fc8d1704f8dd2329e0 created.

pack size = 5976610 bytes

$ git-repack -a -d
[...]
Total 16548, written 16548 (delta 11030), reused 16548 (delta 11030)
Pack pack-af9d39abfcb5fd6fd554f7fc8d1704f8dd2329e0 created.

Pack size =  5976610 bytes

So in this case it took 2 itterations before converging on a smaller 
pack by 55473 bytes.

I thought the reuse logic might sacrifice a bit on compression given the 
speed boost, but I don't get why it is the opposite in practice and that 
-f doesn't produce the smallest pack up front.


Nicolas

```

## Johannes Schindelin, 2006-04-08 22:11

Subject: Re: Funny repack behaviour
Message-ID: <Pine.LNX.4.63.0604090010120.9176@wbgn013.biozentrum.uni-wuerzburg.de>
URL: https://gitlist.dev/e/Pine.LNX.4.63.0604090010120.9176%40wbgn013.biozentrum.uni-wuerzburg.de
In-Reply-To: <Pine.LNX.4.64.0604081528070.2215@localhost.localdomain>

```
Hi,

On Sat, 8 Apr 2006, Nicolas Pitre wrote:

> On Sat, 8 Apr 2006, Johannes Schindelin wrote:
> 
> > Hi,
> > 
> > I just accidentally reran "git-repack -a -d" on a repository, where I just 
> > had run it. And I noticed a funny thing: Of about 4000 objects, it reused 
> > all but 8. So I reran it, and it reused all but 2. I ran it once again, 
> > and it reused all.
> > 
> > The really funny thing is: it created the same pack every time!
> 
> Probably not.  Subsequent packs were most probably even smaller !

Oh, you're right. I was tricked by the identical pack-names. Somehow I 
forgot that the pack name just reflects a hash of the _unpacked_ objects, 
not the pack file itself.

Sorry for the noise.

Ciao,
Dscho

```