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From: Derrick Stolee <stolee@gmail.com>
To: Jonathan Tan <jonathantanmy@google.com>, gitgitgadget@gmail.com
Cc: git@vger.kernel.org, sandals@crustytoothpaste.net,
	steadmon@google.com, jrnieder@gmail.com, peff@peff.net,
	congdanhqx@gmail.com, phillip.wood123@gmail.com,
	emilyshaffer@google.com, sluongng@gmail.com,
	derrickstolee@github.com, dstolee@microsoft.com
Subject: Re: [PATCH v3 6/8] maintenance: add incremental-repack task
Date: Thu, 24 Sep 2020 10:05:17 -0400	[thread overview]
Message-ID: <691ac9f0-0678-8c95-18ad-7b54f92ae531@gmail.com> (raw)
In-Reply-To: <20200922232654.914862-1-jonathantanmy@google.com>

On 9/22/2020 7:26 PM, Jonathan Tan wrote:
>> +incremental-repack::
>> +	The `incremental-repack` job repacks the object directory
>> +	using the `multi-pack-index` feature. In order to prevent race
>> +	conditions with concurrent Git commands, it follows a two-step
>> +	process.
> 
> [snip]
> 
>> First, it deletes any pack-files included in the
>> +	`multi-pack-index` where none of the objects in the
>> +	`multi-pack-index` reference those pack-files; this only happens
>> +	if all objects in the pack-file are also stored in a newer
>> +	pack-file. Second, it selects a group of pack-files whose "expected
>> +	size" is below the batch size until the group has total expected
>> +	size at least the batch size; see the `--batch-size` option for
>> +	the `repack` subcommand in linkgit:git-multi-pack-index[1]. The
>> +	default batch-size is zero, which is a special case that attempts
>> +	to repack all pack-files into a single pack-file.
> 
> This lacks the detail of what happens to the selected group of packfiles
> (in the second step) - in particular, that a new packfile is created and
> the MIDX is rewritten so that all references to the selected group are
> updated to refer to the new packfile instead, thus making it possible to
> delete the selected group of packfiles in a subsequent first step. All
> this is explained in the documentation of git-multi-pack-index (expire
> and repack), though, so it might be better to refer to that. E.g.

Here is my attempt to incorporate your recommendations into this doc:

incremental-repack::
	The `incremental-repack` job repacks the object directory
	using the `multi-pack-index` feature. In order to prevent race
	conditions with concurrent Git commands, it follows a two-step
	process. First, it calls `git multi-pack-index expire` to delete
	pack-files unreferenced by the `multi-pack-index` file. Second, it
	calls `git multi-pack-index repack` to select several small
	pack-files and repack them into a bigger one, and then update the
	`multi-pack-index` entries that refer to the small pack-files to
	refer to the new pack-file. This prepares those small pack-files
	for deletion upon the next run of `git multi-pack-index expire`.
	The selection of the small pack-files is such that the expected
	size of the big pack-file is at least the batch size; see the
	`--batch-size` option for the `repack` subcommand in
	linkgit:git-multi-pack-index[1]. The default batch-size is zero,
	which is a special case that attempts to repack all pack-files
	into a single pack-file.

> Do we need get_midx_filename() to be global?

No, that does not appear to be important (to this patch). It _was_
necessary when doing the "verify, then delete if problematic" mode.
Thanks for catching it now that it is not necessary.

Thanks,
-Stolee
 


  reply	other threads:[~2020-09-24 14:05 UTC|newest]

Thread overview: 66+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-08-06 16:30 [PATCH 0/9] Maintenance II: prefetch, loose-objects, incremental-repack tasks Derrick Stolee via GitGitGadget
2020-08-06 16:30 ` [PATCH 1/9] fetch: optionally allow disabling FETCH_HEAD update Junio C Hamano via GitGitGadget
2020-08-12 23:10   ` Emily Shaffer
2020-08-13  0:03     ` Junio C Hamano
2020-08-13  1:45       ` Jonathan Nieder
2020-08-13  4:37       ` [PATCH v3] " Junio C Hamano
2020-08-14  1:13         ` Derrick Stolee
2020-08-14  1:32           ` Junio C Hamano
2020-08-06 16:30 ` [PATCH 2/9] maintenance: add prefetch task Derrick Stolee via GitGitGadget
2020-08-12 23:10   ` Emily Shaffer
2020-08-14  1:28     ` Derrick Stolee
2020-08-06 16:30 ` [PATCH 3/9] maintenance: add loose-objects task Derrick Stolee via GitGitGadget
2020-08-12 23:10   ` Emily Shaffer
2020-08-14  1:46     ` Derrick Stolee
2020-08-06 16:30 ` [PATCH 4/9] maintenance: create auto condition for loose-objects Derrick Stolee via GitGitGadget
2020-08-06 16:30 ` [PATCH 5/9] midx: enable core.multiPackIndex by default Derrick Stolee via GitGitGadget
2020-08-06 16:30 ` [PATCH 6/9] midx: use start_delayed_progress() Derrick Stolee via GitGitGadget
2020-08-06 16:30 ` [PATCH 7/9] maintenance: add incremental-repack task Derrick Stolee via GitGitGadget
2020-08-06 16:30 ` [PATCH 8/9] maintenance: auto-size incremental-repack batch Derrick Stolee via GitGitGadget
2020-08-06 17:02   ` Son Luong Ngoc
2020-08-06 18:13     ` Derrick Stolee
2020-08-06 16:30 ` [PATCH 9/9] maintenance: add incremental-repack auto condition Derrick Stolee via GitGitGadget
2020-08-18 14:25 ` [PATCH v2 0/9] Maintenance II: prefetch, loose-objects, incremental-repack tasks Derrick Stolee via GitGitGadget
2020-08-18 14:25   ` [PATCH v2 1/9] fetch: optionally allow disabling FETCH_HEAD update Junio C Hamano via GitGitGadget
2020-08-18 14:25   ` [PATCH v2 2/9] maintenance: add prefetch task Derrick Stolee via GitGitGadget
2020-08-18 14:25   ` [PATCH v2 3/9] maintenance: add loose-objects task Derrick Stolee via GitGitGadget
2020-08-18 14:25   ` [PATCH v2 4/9] maintenance: create auto condition for loose-objects Derrick Stolee via GitGitGadget
2020-08-18 14:25   ` [PATCH v2 5/9] midx: enable core.multiPackIndex by default Derrick Stolee via GitGitGadget
2020-08-18 14:25   ` [PATCH v2 6/9] midx: use start_delayed_progress() Derrick Stolee via GitGitGadget
2020-08-18 14:25   ` [PATCH v2 7/9] maintenance: add incremental-repack task Derrick Stolee via GitGitGadget
2020-08-18 14:25   ` [PATCH v2 8/9] maintenance: auto-size incremental-repack batch Derrick Stolee via GitGitGadget
2020-08-18 14:25   ` [PATCH v2 9/9] maintenance: add incremental-repack auto condition Derrick Stolee via GitGitGadget
2020-08-25 18:36   ` [PATCH v3 0/8] Maintenance II: prefetch, loose-objects, incremental-repack tasks Derrick Stolee via GitGitGadget
2020-08-25 18:36     ` [PATCH v3 1/8] maintenance: add prefetch task Derrick Stolee via GitGitGadget
2020-09-22 23:05       ` Jonathan Tan
2020-08-25 18:36     ` [PATCH v3 2/8] maintenance: add loose-objects task Derrick Stolee via GitGitGadget
2020-09-22 23:09       ` Jonathan Tan
2020-09-24 13:45         ` Derrick Stolee
2020-08-25 18:36     ` [PATCH v3 3/8] maintenance: create auto condition for loose-objects Derrick Stolee via GitGitGadget
2020-09-22 23:15       ` Jonathan Tan
2020-09-24 13:51         ` Derrick Stolee
2020-08-25 18:36     ` [PATCH v3 4/8] midx: enable core.multiPackIndex by default Derrick Stolee via GitGitGadget
2020-09-22 23:16       ` Jonathan Tan
2020-09-24 13:53         ` Derrick Stolee
2020-08-25 18:36     ` [PATCH v3 5/8] midx: use start_delayed_progress() Derrick Stolee via GitGitGadget
2020-08-25 18:36     ` [PATCH v3 6/8] maintenance: add incremental-repack task Derrick Stolee via GitGitGadget
2020-09-22 23:26       ` Jonathan Tan
2020-09-24 14:05         ` Derrick Stolee [this message]
2020-09-24 22:01           ` Jonathan Tan
2020-08-25 18:36     ` [PATCH v3 7/8] maintenance: auto-size incremental-repack batch Derrick Stolee via GitGitGadget
2020-08-25 18:36     ` [PATCH v3 8/8] maintenance: add incremental-repack auto condition Derrick Stolee via GitGitGadget
2020-09-22 23:52       ` Jonathan Tan
2020-08-25 20:59     ` [PATCH v3 0/8] Maintenance II: prefetch, loose-objects, incremental-repack tasks Junio C Hamano
2020-08-26 15:15     ` Son Luong Ngoc
2020-08-26 16:21       ` Derrick Stolee
2020-09-25 12:33     ` [PATCH v4 " Derrick Stolee via GitGitGadget
2020-09-25 12:33       ` [PATCH v4 1/8] maintenance: add prefetch task Derrick Stolee via GitGitGadget
2020-09-25 12:33       ` [PATCH v4 2/8] maintenance: add loose-objects task Derrick Stolee via GitGitGadget
2020-09-25 12:33       ` [PATCH v4 3/8] maintenance: create auto condition for loose-objects Derrick Stolee via GitGitGadget
2020-09-25 18:00         ` Junio C Hamano
2020-09-25 18:43           ` Derrick Stolee
2020-09-25 12:33       ` [PATCH v4 4/8] midx: enable core.multiPackIndex by default Derrick Stolee via GitGitGadget
2020-09-25 12:33       ` [PATCH v4 5/8] midx: use start_delayed_progress() Derrick Stolee via GitGitGadget
2020-09-25 12:33       ` [PATCH v4 6/8] maintenance: add incremental-repack task Derrick Stolee via GitGitGadget
2020-09-25 12:33       ` [PATCH v4 7/8] maintenance: auto-size incremental-repack batch Derrick Stolee via GitGitGadget
2020-09-25 12:33       ` [PATCH v4 8/8] maintenance: add incremental-repack auto condition Derrick Stolee via GitGitGadget

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