git@vger.kernel.org mailing list mirror (one of many)
 help / color / mirror / code / Atom feed
From: Shawn Pearce <spearce@spearce.org>
To: Colby Ranger <cranger@google.com>
Cc: "Jeff King" <peff@peff.net>, "Vicent Martí" <tanoku@gmail.com>,
	"Junio C Hamano" <gitster@pobox.com>, git <git@vger.kernel.org>
Subject: Re: [PATCH 09/16] documentation: add documentation for the bitmap format
Date: Mon, 1 Jul 2013 12:13:25 -0700	[thread overview]
Message-ID: <CAJo=hJv=rb2S1DqERQ9GJRQkix=Z5pG2jEyghVDcCHPSF7AKDA@mail.gmail.com> (raw)
In-Reply-To: <CAFFbUKKm89n0HG6xUhYMLs_yjRJ8n0jFtOEEN=vXxJfWKLx5FA@mail.gmail.com>

On Mon, Jul 1, 2013 at 11:47 AM, Colby Ranger <cranger@google.com> wrote:
>> But I think we are comparing
>> apples to steaks here, Vincent is (rightfully) concerned about process
>> startup performance, whereas our timings were assuming the process was
>> already running.
>>
>
> I did some timing on loading the reverse index for the kernel and it
> is pretty slow (~1200ms). I just submitted a fix to do a bucket sort
> and reduced that to ~450ms, which is still slow but much better:
> https://eclipse.googlesource.com/jgit/jgit/+/6cc532a43cf28403cb623d3df8600a2542a40a43%5E%21/

A reverse index that is hot in RAM would obviously load in about 0ms.
But a cold load of a reverse index that uses only 4 bytes per object
(as Colby did here) for 3.1M objects could take ~590ms to read from
disk, assuming spinning media moving 20 MiB/s. If 8 byte offsets were
also stored this could be more like 1700ms.

Numbers obviously get better if the spinning media can transfer at 40
MiB/s, now its more like 295ms for 4 bytes/object and 885ms for 12
bytes/object.

I think its still reasonable to compute the reverse index on the fly.
But JGit certainly does have the benefit of reusing it across requests
by relying on process memory based caches. C Git needs to rely on the
kernel buffer cache, which requires this data be written out to a file
to be shared.

  reply	other threads:[~2013-07-01 19:13 UTC|newest]

Thread overview: 64+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2013-06-24 23:22 [PATCH 00/16] Speed up Counting Objects with bitmap data Vicent Marti
2013-06-24 23:22 ` [PATCH 01/16] list-objects: mark tree as unparsed when we free its buffer Vicent Marti
2013-06-24 23:22 ` [PATCH 02/16] sha1_file: refactor into `find_pack_object_pos` Vicent Marti
2013-06-25 13:59   ` Thomas Rast
2013-06-24 23:23 ` [PATCH 03/16] pack-objects: use a faster hash table Vicent Marti
2013-06-25 14:03   ` Thomas Rast
2013-06-26  2:14     ` Jeff King
2013-06-26  4:47       ` Jeff King
2013-06-25 17:58   ` Ramkumar Ramachandra
2013-06-25 22:48   ` Junio C Hamano
2013-06-25 23:09     ` Vicent Martí
2013-06-24 23:23 ` [PATCH 04/16] pack-objects: make `pack_name_hash` global Vicent Marti
2013-06-24 23:23 ` [PATCH 05/16] revision: allow setting custom limiter function Vicent Marti
2013-06-24 23:23 ` [PATCH 06/16] sha1_file: export `git_open_noatime` Vicent Marti
2013-06-24 23:23 ` [PATCH 07/16] compat: add endinanness helpers Vicent Marti
2013-06-25 13:08   ` Peter Krefting
2013-06-25 13:25     ` Vicent Martí
2013-06-27  5:56       ` Peter Krefting
2013-06-24 23:23 ` [PATCH 08/16] ewah: compressed bitmap implementation Vicent Marti
2013-06-25  1:10   ` Junio C Hamano
2013-06-25 22:51     ` Junio C Hamano
2013-06-25 15:38   ` Thomas Rast
2013-06-24 23:23 ` [PATCH 09/16] documentation: add documentation for the bitmap format Vicent Marti
2013-06-25  5:42   ` Shawn Pearce
2013-06-25 19:33     ` Vicent Martí
2013-06-25 21:17       ` Junio C Hamano
2013-06-25 22:08         ` Vicent Martí
2013-06-27  1:11           ` Shawn Pearce
2013-06-27  2:36             ` Vicent Martí
2013-06-27  2:45               ` Jeff King
2013-06-27 16:07                 ` Shawn Pearce
2013-06-27 17:17                   ` Jeff King
2013-07-01 18:47                   ` Colby Ranger
2013-07-01 19:13                     ` Shawn Pearce [this message]
2013-07-07  9:46                     ` Jeff King
2013-07-07 17:27                       ` Shawn Pearce
2013-06-26  5:11       ` Jeff King
2013-06-26 18:41         ` Colby Ranger
2013-06-26 22:33           ` Colby Ranger
2013-06-27  0:53             ` Colby Ranger
2013-06-27  1:32               ` Shawn Pearce
2013-06-27  1:29         ` Shawn Pearce
2013-06-25 15:58   ` Thomas Rast
2013-06-25 22:30     ` Vicent Martí
2013-06-26 23:12       ` Thomas Rast
2013-06-26 23:19         ` Thomas Rast
2013-06-24 23:23 ` [PATCH 10/16] pack-objects: use bitmaps when packing objects Vicent Marti
2013-06-25 12:48   ` Ramkumar Ramachandra
2013-06-25 15:58   ` Thomas Rast
2013-06-25 23:06   ` Junio C Hamano
2013-06-25 23:14     ` Vicent Martí
2013-06-24 23:23 ` [PATCH 11/16] rev-list: add bitmap mode to speed up lists Vicent Marti
2013-06-25 16:22   ` Thomas Rast
2013-06-26  1:45     ` Vicent Martí
2013-06-26 23:13       ` Thomas Rast
2013-06-26  5:22     ` Jeff King
2013-06-24 23:23 ` [PATCH 12/16] pack-objects: implement bitmap writing Vicent Marti
2013-06-24 23:23 ` [PATCH 13/16] repack: consider bitmaps when performing repacks Vicent Marti
2013-06-25 23:00   ` Junio C Hamano
2013-06-25 23:16     ` Vicent Martí
2013-06-24 23:23 ` [PATCH 14/16] sha1_file: implement `nth_packed_object_info` Vicent Marti
2013-06-24 23:23 ` [PATCH 15/16] write-bitmap: implement new git command to write bitmaps Vicent Marti
2013-06-24 23:23 ` [PATCH 16/16] rev-list: Optimize --count using bitmaps too Vicent Marti
2013-06-25 16:05 ` [PATCH 00/16] Speed up Counting Objects with bitmap data Thomas Rast

Reply instructions:

You may reply publicly to this message via plain-text email
using any one of the following methods:

* Save the following mbox file, import it into your mail client,
  and reply-to-all from there: mbox

  Avoid top-posting and favor interleaved quoting:
  https://en.wikipedia.org/wiki/Posting_style#Interleaved_style

  List information: http://vger.kernel.org/majordomo-info.html

* Reply using the --to, --cc, and --in-reply-to
  switches of git-send-email(1):

  git send-email \
    --in-reply-to='CAJo=hJv=rb2S1DqERQ9GJRQkix=Z5pG2jEyghVDcCHPSF7AKDA@mail.gmail.com' \
    --to=spearce@spearce.org \
    --cc=cranger@google.com \
    --cc=git@vger.kernel.org \
    --cc=gitster@pobox.com \
    --cc=peff@peff.net \
    --cc=tanoku@gmail.com \
    /path/to/YOUR_REPLY

  https://kernel.org/pub/software/scm/git/docs/git-send-email.html

* If your mail client supports setting the In-Reply-To header
  via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line before the message body.
Code repositories for project(s) associated with this public inbox

	https://80x24.org/mirrors/git.git

This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for read-only IMAP folder(s) and NNTP newsgroup(s).