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From: Shawn Pearce <spearce@spearce.org>
To: Junio C Hamano <gitster@pobox.com>
Cc: git <git@vger.kernel.org>, Jeff King <peff@peff.net>,
	Michael Haggerty <mhagger@alum.mit.edu>,
	David Borowitz <dborowitz@google.com>
Subject: Re: reftable [v4]: new ref storage format
Date: Tue, 1 Aug 2017 09:08:26 -0700	[thread overview]
Message-ID: <CAJo=hJtVat6r6WCghSr3M8PBmEzdjpGt2tgdObvGFKPqQ=myOQ@mail.gmail.com> (raw)
In-Reply-To: <CAJo=hJurMO=eQP3xctwTX9cO3yTZogJsw5HMztWjB8JHHtJ=fQ@mail.gmail.com>

On Mon, Jul 31, 2017 at 4:43 PM, Shawn Pearce <spearce@spearce.org> wrote:
> On Mon, Jul 31, 2017 at 12:42 PM, Junio C Hamano <gitster@pobox.com> wrote:
>>
>> As a block cannot be longer than 16MB, allocating uint32 to a
>> restart offset may be a bit overkill.  I do not know if it is worth
>> attempting to pack 1/3 more restart entries in a block by using
>> uint24, though.
>
> I don't think its worth the annoyance in code that has to deal with
> this field. An example 87k ref repository with a 4k block size has ~9
> restarts per block and ~19 bytes of padding. Using uint24 saves us 9
> bytes, yet the average ref here costs 27 bytes. We aren't likely to
> fill the block with another ref, or another restart point.

I thought about this more. We can fit an additional ref per block in
some cases. It saves ~20 KiB for one of my example repositories if
restart_offset is a uint24.

Given that readers have to deal with these being unaligned loads
anyway, its not significantly harder to work with uint24 vs. uint32.
So I've changed the definition to be uint24.

  reply	other threads:[~2017-08-01 16:12 UTC|newest]

Thread overview: 34+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2017-07-31  3:51 Shawn Pearce
2017-07-31 17:41 ` Dave Borowitz
2017-07-31 19:01 ` Stefan Beller
2017-07-31 23:05   ` Shawn Pearce
2017-07-31 19:42 ` Junio C Hamano
2017-07-31 23:43   ` Shawn Pearce
2017-08-01 16:08     ` Shawn Pearce [this message]
2017-08-01  6:41 ` Michael Haggerty
2017-08-01 20:23   ` Shawn Pearce
2017-08-02  0:49     ` Michael Haggerty
2017-08-01 23:27   ` Shawn Pearce
2017-08-01 23:54     ` Shawn Pearce
2017-08-02  1:51     ` Michael Haggerty
2017-08-02  2:38       ` Shawn Pearce
2017-08-02  9:28         ` Jeff King
2017-08-02 15:17           ` Shawn Pearce
2017-08-02 16:51             ` Junio C Hamano
2017-08-02 17:28             ` Jeff King
2017-08-02 12:20         ` Dave Borowitz
2017-08-02 17:18           ` Jeff King
2017-08-03 18:38         ` Michael Haggerty
2017-08-03 22:26           ` Shawn Pearce
2017-08-03 22:48             ` Michael Haggerty
2017-08-04  2:50               ` Shawn Pearce
2017-08-05 21:00       ` Shawn Pearce
2017-08-01 13:54 ` Dave Borowitz
2017-08-01 15:27   ` Shawn Pearce
2017-08-02 19:50 ` Junio C Hamano
2017-08-02 20:28   ` Jeff King
2017-08-03 22:17     ` Shawn Pearce
2017-08-03  1:50   ` Junio C Hamano
2017-08-03  2:21     ` Shawn Pearce
2017-08-03  2:36       ` Junio C Hamano
2017-08-02 19:54 ` Stefan Beller

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