Re: Hacking on PostgreSQL via GIT

Jim C. Nasby wrote:
> Not bad... took you 40 lines to answer my question. Let's see if I can
> beat that...

Sure - it'll be 1 line when it's wrapped in a shell script. And then
we'll be even.

> I understand the argument about metadata and all, and largely agree with
> it. But on the other hand I think a version identifier is a critical
> piece of information; it's just as critical as the file name when it
> comes to identifying the information contained in the file.

Surely. It is important, but it's metadata and belongs elsewhere. That
metadata _is_ important doesn't mean you corrupt _data_ with it.

Just imagine that MySQL users were used to getting their SQL engine
expand $Oid$ $Tablename$ $PrimayKey$ in TEXT fields. And that when
INSERT/UPDATEing those were collapsed. And in comparisons too. Wouldn't
you say "that's metadata, can be queried in a thousand ways, does not
belong in the middle of the data"?

And the _really_ interesting version identifier is usually the "commit"
identifier, which gives you a SHA1 of the whole src directory and the
history. Projects that use git usually include that SHA1 in their build
script, so even if a user compiles off a daily snapshot or a checkout on
a random branch of your SCM, you can just ask them "what's the build
identifier?" and they'll give you a SHA1.

Actually, git can spit a nicer build identifier that includes the latest
tag, so if you see the identifier being

v8.2.<sha1>

You know it's not 8.2 "release" but a commit soon after it, identified
by that SHA1. GIT uses that during its build to insert the version
identifier, so:

$ git --version
git version 1.5.1.gf8ce

With that in your hand, you can say

# show me what commits on top of the tagged 1.5.1 have I got:
$ git log 1.5.1..gf8ce

# file src/lib/foo.c at this exact commit
git show gf8ce:src/lib/foo.c

So if you use this identifier (just call `git version`) to

- name your tarballs
- create a "build-id" file at tarball creation time
- tag your builds with a version id

And then when you have code out there in the wild, and people report
bugs or send you patches, there's a good identifier you can ask for that
covers _all_ the files.

If it happens that someone reports a bug and says they have 8.2.gg998
and you don't seem to have any gg998 commit after 8.2, you can say with
confidence: you are running some a patched Pg - please repro with a
pristine copy (or show us your code!) :-)

cheers,

m
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