Re: Antw: Re: non-smooth progress indication for git fsck and git gc
- From
- Ulrich Windl <ulrich.windl@rz.uni-regensburg.de>
- Date
- Aug 20, 2018, 09:37 UTC
- Message-ID
- <5B7A8BD3020000A10002CDE1@gwsmtp1.uni-regensburg.de>
- In-Reply-To
- <87woslpg9i.fsf@evledraar.gmail.com>
Hi!
Here are some stats from the repository. First the fast import ones (which had good performance, but probably all cached, also):
% git fast-import <../git-stream
/usr/lib/git/git-fast-import statistics:
---------------------------------------------------------------------
Alloc'd objects: 55000
Total objects: 51959 ( 56 duplicates )
blobs : 47991 ( 0 duplicates 0 deltas of
0 attempts)
trees : 3946 ( 56 duplicates 994 deltas of
3929 attempts)
commits: 22 ( 0 duplicates 0 deltas of
0 attempts)
tags : 0 ( 0 duplicates 0 deltas of
0 attempts)
Total branches: 15 ( 15 loads )
marks: 1048576 ( 48013 unique )
atoms: 43335
Memory total: 9611 KiB
pools: 7033 KiB
objects: 2578 KiB
---------------------------------------------------------------------
pack_report: getpagesize() = 4096
pack_report: core.packedGitWindowSize = 1073741824
pack_report: core.packedGitLimit = 8589934592
pack_report: pack_used_ctr = 1780
pack_report: pack_mmap_calls = 23
pack_report: pack_open_windows = 1 / 1
pack_report: pack_mapped = 2905751 / 2905751
---------------------------------------------------------------------Then the output from git-sizer:
Processing blobs: 47991 Processing trees: 3946 Processing commits: 22 Matching commits to trees: 22 Processing annotated tags: 0 Processing references: 15 | Name | Value | Level of concern | | ---------------------------- | --------- | ------------------------------ | | Overall repository size | | | | * Blobs | | | | * Total size | 13.7 GiB | * | | | | | | Biggest objects | | | | * Trees | | | | * Maximum entries [1] | 13.4 k | ************* | | * Blobs | | | | * Maximum size [2] | 279 MiB | ***************************** | | | | | | Biggest checkouts | | | | * Maximum path depth [3] | 10 | * | | * Maximum path length [3] | 130 B | * | | * Total size of files [3] | 8.63 GiB | ********* |
[1] b701345cbd4317276568b9d9890fd77f38933bdc (refs/heads/master:Resources/default/CIFP) [2] 19f54c4a7595667329c1be23200234f0fe50ac56 (refs/heads/master:Resources/default/apt.dat) [3] b0e3d3a2b7f2504117408f13486c905a8eb8fb1e (refs/heads/master^{tree})
Some notes: [1] is a directory with many short (typically < 1kB) text files [2] is a very large text file with many changes [3] Yes, some paths are long
Regards, Ulrich
>>> Ævar Arnfjörð Bjarmason <avarab@gmail.com> schrieb am 20.08.2018 um 10:57
in Nachricht <87woslpg9i.fsf@evledraar.gmail.com>:
Show 23 quoted lines
> On Mon, Aug 20 2018, Ulrich Windl wrote: > >>>>> Jeff King <peff@peff.net> schrieb am 16.08.2018 um 22:55 in Nachricht >> <20180816205556.GA8257@sigill.intra.peff.net>: >>> On Thu, Aug 16, 2018 at 10:35:53PM +0200, Ævar Arnfjörð Bjarmason wrote: >>> >>>> This is all interesting, but I think unrelated to what Ulrich is talking >>>> about. Quote: >>>> >>>> Between the two phases of "git fsck" (checking directories and >>>> checking objects) there was a break of several seconds where no >>>> progress was indicated >>>> >>>> I.e. it's not about the pause you get with your testcase (which is >>>> certainly another issue) but the break between the two progress bars. >>> >>> I think he's talking about both. What I said responds to this: >> >> Hi guys! >> >> Yes, I was wondering what git does between the two visible phases, and > between >> the lines I was suggesting another progress message between those phases.
At
Show 30 quoted lines
>> least the maximum unspecific three-dot-message "Thinking..." could be > displayed >> ;-) Of course anything more appropriate would be welcome. >> Also that message should only be displayed if it's foreseeable that the >> operation will take significant time. In my case (I just repeated it a few >> minutes ago) the delay is significant (at least 10 seconds). As noted > earlier I >> was hoping to capture the timing in a screencast, but it seems all the > delays >> were just optimized away in the recording. >> >>> >>>> >> During "git gc" the writing objects phase did not update for some >>>> >> seconds, but then the percentage counter jumped like from 15% to 42%. >>> >>> But yeah, I missed that the fsck thing was specifically about a break >>> between two meters. That's a separate problem, but also worth >>> discussing (and hopefully much easier to address). >>> >>>> If you fsck this repository it'll take around (on my spinning rust >>>> server) 30 seconds between 100% of "Checking object directories" before >>>> you get any output from "Checking objects". >>>> >>>> The breakdown of that is (this is from approximate eyeballing): >>>> >>>> * We spend 1-3 seconds just on this: >>>> >>> >> >
https://github.com/git/git/blob/63749b2dea5d1501ff85bab7b8a7f64911d21dea/pack
Show 10 quoted lines
>> >>> -check.c#L181 >>> >>> OK, so that's checking the sha1 over the .idx file. We could put a meter >>> on that. I wouldn't expect it to generally be all that slow outside of >>> pathological cases, since it scales with the number of objects (and 1s >>> is our minimum update anyway, so that might be OK as-is). Your case has >>> 13M objects, which is quite large. >> >> Sometimes an oldish CPU could bring performance surprises, maybe. Anyway
my
>> CPU is question is an AMD Phenom2 quad-core with 3.2GHz nominal, and there
Show 9 quoted lines
> is a >> classic spinning disk with 5400RPM built in... >> >>> >>>> * We spend the majority of the ~30s on this: >>>> >>> >> >
https://github.com/git/git/blob/63749b2dea5d1501ff85bab7b8a7f64911d21dea/pack
Show 27 quoted lines
>> >>> -check.c#L70-L79 >>> >>> This is hashing the actual packfile. This is potentially quite long, >>> especially if you have a ton of big objects. >> >> That seems to apply. BTW: Is there a way go get some repository statistics >> like a histogram of object sizes (or whatever that might be useful to help >> making decisions)? > > The git-sizer program is really helpful in this regard: > https://github.com/github/git-sizer > >>> >>> I wonder if we need to do this as a separate step anyway, though. Our >>> verification is based on index-pack these days, which means it's going >>> to walk over the whole content as part of the "Indexing objects" step to >>> expand base objects and mark deltas for later. Could we feed this hash >>> as part of that walk over the data? It's not going to save us 30s, but >>> it's likely to be more efficient. And it would fold the effort naturally >>> into the existing progress meter. >>> >>>> * Wes spend another 3-5 seconds on this QSORT: >>>> >>> >> >
https://github.com/git/git/blob/63749b2dea5d1501ff85bab7b8a7f64911d21dea/pack
Show 27 quoted lines
>>
>>> -check.c#L105
>>>
>>> That's a tough one. I'm not sure how we'd count it (how many compares we
>>> do?). And each item is doing so little work that hitting the progress
>>> code may make things noticeably slower.
>>
>> If it's sorting, maybe add some code like (wild guess):
>>
>> if (objects_to_sort > magic_number)
>> message("Sorting something...");
>
> I think a good solution to these cases is to just introduce something to
> the progress.c mode where it learns how to display a counter where we
> don't know what the end-state will be. Something like your proposed
> magic_number can just be covered under the more general case where we
> don't show the progress bar unless it's been 1 second (which I believe
> is the default).
>
>>>
>>> Again, your case is pretty big. Just based on the number of objects,
>>> linux.git should be 1.5-2.5 seconds on your machine for the same
>>> operation. Which I think may be small enough to ignore (or even just
>>> print a generic before/after). It's really the 30s packfile hash that's
>>> making the whole thing so terrible.
>>>
>>> -Peff