From: Derrick Stolee Date: Wed, 07 Feb 2018 15:10:29 GMT Subject: Re: [PATCH v2 04/14] commit-graph: implement construct_commit_graph() Message-ID: <31192658-5fe6-fcc6-7b9c-8e6b298e2474@gmail.com> In-Reply-To: On 2/7/2018 10:08 AM, SZEDER Gábor wrote: > On Mon, Feb 5, 2018 at 5:06 PM, Derrick Stolee wrote: >> On 2/2/2018 10:32 AM, SZEDER Gábor wrote: >>> In my git repo, with 9 pack files at the moment, i.e. not that big a >>> repo and not that many pack files: >>> >>> $ time ./git commit-graph --write --update-head >>> 4df41a3d1cc408b7ad34bea87b51ec4ccbf4b803 >>> >>> real 0m27.550s >>> user 0m27.113s >>> sys 0m0.376s >>> >>> In comparison, performing a good old revision walk to gather all the >>> info that is written into the graph file: >>> >>> $ time git log --all --topo-order --format='%H %T %P %cd' |wc -l >>> 52954 >>> >>> real 0m0.903s >>> user 0m0.972s >>> sys 0m0.058s >> >> Two reasons this is in here: >> >> (1) It's easier to get the write implemented this way and add the reachable >> closure later (which I do). >> >> (2) For GVFS, we want to add all commits that arrived in a "prefetch pack" >> to the graph even if we do not have a ref that points to the commit yet. We >> expect many commits to become reachable soon and having them in the graph >> saves a lot of time in merge-base calculations. >> >> So, (1) is for patch simplicity, and (2) is why I want it to be an option in >> the final version. See the --stdin-packs argument later for a way to do this >> incrementally. >> >> I expect almost all users to use the reachable closure method with >> --stdin-commits (and that's how I will integrate automatic updates with >> 'fetch', 'repack', and 'gc' in a later patch). > I see. I was about to ask about the expected use-cases of the > '--stdin-packs' option, considering how much slower it is to enumerate > all objects in pack files, but run out of time after patch 10. > > The run-time using '--stdin-commits' is indeed great: > > $ time { git for-each-ref --format='%(objectname)' refs/heads/ | ./git > commit-graph --write --update-head --stdin-commits ; } > 82fe9a5cd715ff578f01f7f44e0611d7902d20c8 > > real 0m0.985s > user 0m0.916s > sys 0m0.024s > > Considering the run-time difference, I think in the end it would be a > better default for a plain 'git commit-graph --write' to traverse > history from all refs, and it should enumerate pack files only if > explicitly told so via '--stdin-packs'. > > To be clear: I'm not saying that traversing history should already be > the default when introducing construct_commit_graph() and '--write'. If > enumerating pack files keeps the earlier patches simpler and easier to > review, then by all means stick with it, and only change the > '--stdin-*'-less behavior near the end of the series, when all the > building blocks are already in place (but then mention this in the early > commit messages). I will consider this. > I have also noticed a segfault when feeding non-commit object names to > '--stdin-commits', i.e. when I run the above command without restricting > 'git for-each-ref' to branches and it listed object names of tags as > well. > > $ git rev-parse v2.16.1 |./git commit-graph --write --update-head > --stdin-commits > error: Object eb5fcb24f69e13335cf6a6a1b1d4553fa2b0f202 not a commit > error: Object eb5fcb24f69e13335cf6a6a1b1d4553fa2b0f202 not a commit > error: Object eb5fcb24f69e13335cf6a6a1b1d4553fa2b0f202 not a commit > Segmentation fault > > (gdb) bt > #0 __memcpy_avx_unaligned () > at ../sysdeps/x86_64/multiarch/memcpy-avx-unaligned.S:126 > #1 0x00000000004ea97c in sha1write (f=0x356bbf0, buf=0x4, count=20) > at csum-file.c:104 > #2 0x00000000004d98e1 in write_graph_chunk_data (f=0x356bbf0, hash_len=20, > commits=0x3508de0, nr_commits=50615) at commit-graph.c:506 > #3 0x00000000004da9ca in construct_commit_graph ( > pack_dir=0x8ff360 ".git/objects/pack", pack_indexes=0x0, nr_packs=0, > commit_hex=0x8ff790, nr_commits=1) at commit-graph.c:818 > #4 0x000000000044184e in graph_write () at builtin/commit-graph.c:149 > #5 0x0000000000441a8c in cmd_commit_graph (argc=0, argv=0x7fffffffe310, > prefix=0x0) at builtin/commit-graph.c:224 > #6 0x0000000000405a0a in run_builtin (p=0x8ad950 , argc=4, > argv=0x7fffffffe310) at git.c:346 > #7 0x0000000000405ce4 in handle_builtin (argc=4, argv=0x7fffffffe310) > at git.c:555 > #8 0x0000000000405ec8 in run_argv (argcp=0x7fffffffe1cc, argv=0x7fffffffe1c0) > at git.c:607 > #9 0x0000000000406079 in cmd_main (argc=4, argv=0x7fffffffe310) at git.c:684 > #10 0x00000000004a85c8 in main (argc=5, argv=0x7fffffffe308) > at common-main.c:43 I noticed this while preparing v3. I have a fix, but you now remind me that I need to add tags to the test script. Thanks, -Stolee