I haven't looked at it, but would like to ask if you've tested when
you have multiple .mcd's in succession?  Like, if you have,

    Kernel-cmm.100.mcz
    Kernel-cmm.101.mcd
    Kernel-cmm.102.mcd

Does 102 need to have ancestry at least back to 101 (or, 100?) still stored?


On Fri, Apr 7, 2017 at 6:38 AM, Milan Vavra via Squeak-dev
<squeak-dev at lists.squeakfoundation.org> wrote:
> Hi Tobias,
>
> Thanks for asking.
>
> So what is this Monticello-mva.667.mcz good for?
>
> The idea is...
> ... let's make mcd files smaller.
> As small as they can be.
>
> Only containing information relevant to the diff.
>
> No more. No less.
>
> And they can be. A lot smaller.
>
> An order of magnitude smaller compared with the in-trunk version.
> Think 8K instead of 80K for a mcd with one-line changes.
>
> If you have followed the instructions in
> http://lists.squeakfoundation.org/pipermail/squeak-dev/2017-April/194029.html
> to get a current squeak6.0 alpha, you will have seen files like
> Collections-eem.743(ul.742).mcd in your package-cache directory.
>
> If you look at their sizes, you will notice that they are much smaller than
> regular mcz files.
>
> For example.
> A standard snapshot mcz, Collections-ul.742.mcz is 485K.
> A diff mcd, Collections-eem.743(ul.742).mcd is only 84K.
>
> How do you create such files?
>
> Select a version in a Repository Browser, click Diff, select the
> version against which the diff should be made and you get a 'diffy version'.
> If you now click 'Copy' and copy it to a different directory repository,
> an mcd file will be stored there not an mcz file.
>
> Or if you yellow-click a directory repository in Monticello Browser and
> select 'store diffs' then whenever you select a version in Repository
> browser, click 'Copy' to copy to that directory repository, the version
> will be stored there as an mcd file.
>
>
> But what if I told you that that Collections-eem.743(ul.742).mcd could have
> been even smaller. A lot smaller. An order of magnitude smaller.
> Not 84K. Only 4.9K.
> With no loss of information?
>
> I have that converted version sitting on my disk right now.
>
> It were written out with this modification
> http://forum.world.st/The-Inbox-Monticello-mva-667-mcz-tt4941466.html
> http://source.squeak.org/inbox/Monticello-mva.667.mcz to Monticello.
>
> How could it be so small?
>
> Well, by trimming the information stored in the 'version' file in the mcd
> zip archive.
>
> This information grows over time as new versions are added and commit
> comments written. And if not trimmed will gradually take up a significant
> portion of the file's size. Especially for small changes. One-liners. And
> there's no real need to store it all in each mcd file.
>
>
> No information is lost. Because the information that is trimmed is
> readily available in the monticello version against which the diff mcd was
> made.
>
> So the trick is to trim on writing. And attach back from base version on
> reading.
>
> Disk space, network bandwidth is saved.
>
> The version's history appears the same as before when all that redundant
> information were saved in the mcd archive.
>
> So you can write out much smaller mcd files with this modification.
>
> Read them back in and the system will not know the difference.
>
> And if you have old mcd files sitting around with full version info history
> they are read in as before with no surprises.
>
> Does it make sense or which part needs better explanation?
>
> Best Regards,
>
> Milan Vavra
>
>
>
>
>
> --
> View this message in context: http://forum.world.st/The-Inbox-Monticello-mva-667-mcz-tp4941466p4941532.html
> Sent from the Squeak - Dev mailing list archive at Nabble.com.
>