Re: [Bug report] git log shows a wrong history

From: SZEDER Gábor <szeder.dev@gmail.com>
Date: Nov 12, 2022, 07:13 UTC
Message-ID: <20221112071313.GE1159673@szeder.dev>
In-Reply-To: <CABAGCCq-bFYX+9kU-GGWBstjMjOcO1nSQdi6Udugtkd2McO3Tg@mail.gmail.com>

On Sat, Nov 12, 2022 at 12:23:58PM +0800, Adam Lee wrote:

Show 37 quoted lines

> What did you do before the bug happened? (Steps to reproduce your issue)
> 
> ```
> git clone https://github.com/greenplum-db/gpdb-postgres-merge.git
> git_log_reproducer
> 
> cd git_log_reproducer/
> 
> git co -b iteration_REL_12_12 origin/iteration_REL_12_12
> 
> git log
> ```
> 
> What did you expect to happen? (Expected behavior)
> 
> A part of the history is:
> ```
> ...
> commit 9ac9a7fd4138988d744e0b5767883c06c20ffa6f
> commit fe0a9ddbdd7eee572f7321f9680280044fd5f258
> ...
> ```
> 
> What happened instead? (Actual behavior)
> 
> That part of the history is:
> ```
> ...
> commit 9ac9a7fd4138988d744e0b5767883c06c20ffa6f
> commit f9c655d647427b45ae0d7bd9baf3551a013b8ea1
> commit fe0a9ddbdd7eee572f7321f9680280044fd5f258
> ...
> ```
> 
> What's different between what you expected and what actually happened?
> 
> commit f9c655d647427b45ae0d7bd9baf3551a013b8ea1 is at the wrong place.

'git log' shows the commis in reverse chronological order by default, which means that if development happens on multiple parallel running branches, then commits made on different branches might be shown intermixed.

And indeed the commit timestamp of f9c655 is between that of the other two:

  $ git log --format='%H %ct' |grep -A2 ^9ac9a7
  9ac9a7fd4138988d744e0b5767883c06c20ffa6f 1657232286
  f9c655d647427b45ae0d7bd9baf3551a013b8ea1 1657195677
  fe0a9ddbdd7eee572f7321f9680280044fd5f258 1657177514

(Using the seconds since epoch timestamp format here, because those three commits were made in different time zones, making their ordering by simply looking at them not quite that straightforward.)

Showing commits in topographical order "avoids showing commits on multiple lines of history intermixed" (quoting the manpage), although at the cost of slightly more processing time:

  $ git log --format='%H %ct' --topo-order |grep -A2 ^9ac9a7
  9ac9a7fd4138988d744e0b5767883c06c20ffa6f 1657232286
  fe0a9ddbdd7eee572f7321f9680280044fd5f258 1657177514
  5a9a4091ad1a187cec9d7da0faafac15b088fe60 1657172979

> `git log --graph` is fine.

'--graph' implies '--topo-order' by default.