- Concerning Git's Packing Heuristics
- ===================================
+Concerning Git's Packing Heuristics
+===================================
Oh, here's a really stupid question:
Where do I go
to learn the details
- of git's packing heuristics?
+ of Git's packing heuristics?
Be careful what you ask!
-Followers of the git, please open the git IRC Log and turn to
+Followers of the Git, please open the Git IRC Log and turn to
February 10, 2006.
It's a rare occasion, and we are joined by the King Git Himself,
Let's listen in!
<njs`> Oh, here's a really stupid question -- where do I go to
- learn the details of git's packing heuristics? google avails
+ learn the details of Git's packing heuristics? google avails
me not, reading the source didn't help a lot, and wading
through the whole mailing list seems less efficient than any
of that.
<linus> njs, I don't think the docs exist. That's something where
I don't think anybody else than me even really got involved.
- Most of the rest of git others have been busy with (especially
+ Most of the rest of Git others have been busy with (especially
Junio), but packing nobody touched after I did it.
It's cryptic, yet vague. Linus in style for sure. Wise men
And switch. That ought to do it!
- <linus> Remember: git really doesn't follow files. So what it does is
+ <linus> Remember: Git really doesn't follow files. So what it does is
- generate a list of all objects
- sort the list according to magic heuristics
- walk the list, using a sliding window, seeing if an object
<linus> The "magic" is actually in theory totally arbitrary.
ANY order will give you a working pack, but no, it's not
- ordered by SHA1.
+ ordered by SHA-1.
Before talking about the ordering for the sliding delta
window, let's talk about the recency order. That's more
<njs`> (if only it happened more...)
<linus> Anyway, the pack-file could easily be denser still, but
- because it's used both for streaming (the git protocol) and
+ because it's used both for streaming (the Git protocol) and
for on-disk, it has a few pessimizations.
Actually, it is a made-up word. But it is a made-up word being
In fact, Linus reflects on some Basic Engineering Fundamentals,
design options, etc.
- <linus> More importantly, they allow git to still _conceptually_
+ <linus> More importantly, they allow Git to still _conceptually_
never deal with deltas at all, and be a "whole object" store.
Which has some problems (we discussed bad huge-file
- behaviour on the git lists the other day), but it does mean
- that the basic git concepts are really really simple and
+ behaviour on the Git lists the other day), but it does mean
+ that the basic Git concepts are really really simple and
straightforward.
It's all been quite stable.
<njs`> :-)
<njs`> appreciate the infodump, I really was failing to find the
- details on git packs :-)
+ details on Git packs :-)
And now you know the rest of the story.