Re: [PATCH v3 1/8] maintenance: add prefetch task

From: Jonathan Tan <jonathantanmy@google.com>
To: 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,
	jonathantanmy@google.com, derrickstolee@github.com,
	dstolee@microsoft.com
Subject: Re: [PATCH v3 1/8] maintenance: add prefetch task
Date: Tue, 22 Sep 2020 16:05:35 -0700	[thread overview]
Message-ID: <20200922230535.903375-1-jonathantanmy@google.com> (raw)
In-Reply-To: <da64c51a8182ec13aeed8f0157079fb29a09ee85.1598380599.git.gitgitgadget@gmail.com>

> From: Derrick Stolee <dstolee@microsoft.com>
> 
> When working with very large repositories, an incremental 'git fetch'
> command can download a large amount of data. If there are many other
> users pushing to a common repo, then this data can rival the initial
> pack-file size of a 'git clone' of a medium-size repo.
> 
> Users may want to keep the data on their local repos as close as
> possible to the data on the remote repos by fetching periodically in
> the background. This can break up a large daily fetch into several
> smaller hourly fetches.
> 
> The task is called "prefetch" because it is work done in advance
> of a foreground fetch to make that 'git fetch' command much faster.
> 
> However, if we simply ran 'git fetch <remote>' in the background,
> then the user running a foregroudn 'git fetch <remote>' would lose

-> foreground

I have some more minor comments that I will send as individual replies,
but overall, the patch set looks good to me.

> +static int append_remote(struct remote *remote, void *cbdata)
> +{
> +	struct string_list *remotes = (struct string_list *)cbdata;
> +
> +	string_list_append(remotes, remote->name);
> +	return 0;
> +}
> +
> +static int maintenance_task_prefetch(struct maintenance_run_opts *opts)
> +{
> +	int result = 0;
> +	struct string_list_item *item;
> +	struct string_list remotes = STRING_LIST_INIT_DUP;
> +
> +	if (for_each_remote(append_remote, &remotes)) {
> +		error(_("failed to fill remotes"));
> +		result = 1;
> +		goto cleanup;
> +	}
> +
> +	for_each_string_list_item(item, &remotes)
> +		result |= fetch_remote(item->string, opts);
> +
> +cleanup:
> +	string_list_clear(&remotes, 0);
> +	return result;
> +}

I was wondering why the generation of the list and the iteration was
split up, but I see that you want to attempt to fetch each remote even
if one of them fails.