Re: [PATCH v2 2/2] diff: batch fetching of missing blobs

[Johannes Schindelin <Johannes.Schindelin@gmx.de>]

Hi Jonathan,

On Fri, 29 Mar 2019, Jonathan Tan wrote:

> When running a command like "git show" or "git diff" in a partial clone,
> batch all missing blobs to be fetched as one request.
>
> This is similar to c0c578b33c ("unpack-trees: batch fetching of missing
> blobs", 2017-12-08), but for another command.

Still makes sense ;-)

> diff --git a/diff.c b/diff.c
> index ec5c095199..1eccefb4ef 100644
> --- a/diff.c
> +++ b/diff.c
> @@ -25,6 +25,7 @@
>  #include "packfile.h"
>  #include "parse-options.h"
>  #include "help.h"
> +#include "fetch-object.h"
>
>  #ifdef NO_FAST_WORKING_DIRECTORY
>  #define FAST_WORKING_DIRECTORY 0
> @@ -6366,8 +6367,39 @@ void diffcore_fix_diff_index(void)
>  	QSORT(q->queue, q->nr, diffnamecmp);
>  }
>
> +static void add_if_missing(struct oid_array *to_fetch,
> +			   const struct diff_filespec *filespec)
> +{
> +	if (filespec && filespec->oid_valid &&
> +	    oid_object_info_extended(the_repository, &filespec->oid, NULL,
> +				     OBJECT_INFO_FOR_PREFETCH))
> +		oid_array_append(to_fetch, &filespec->oid);
> +}

Thank you for introducing this, in looks more elegant to my eyes than the
previous iteration.

> +
>  void diffcore_std(struct diff_options *options)
>  {
> +	if (repository_format_partial_clone) {
> +		/*
> +		 * Prefetch the diff pairs that are about to be flushed.
> +		 */
> +		int i;
> +		struct diff_queue_struct *q = &diff_queued_diff;
> +		struct oid_array to_fetch = OID_ARRAY_INIT;
> +
> +		for (i = 0; i < q->nr; i++) {
> +			struct diff_filepair *p = q->queue[i];
> +			add_if_missing(&to_fetch, p->one);
> +			add_if_missing(&to_fetch, p->two);
> +		}
> +		if (to_fetch.nr)
> +			/*
> +			 * NEEDSWORK: Consider deduplicating the OIDs sent.
> +			 */
> +			fetch_objects(repository_format_partial_clone,
> +				      to_fetch.oid, to_fetch.nr);
> +		oid_array_clear(&to_fetch);
> +	}
> +
>  	/* NOTE please keep the following in sync with diff_tree_combined() */
>  	if (options->skip_stat_unmatch)
>  		diffcore_skip_stat_unmatch(options);
> diff --git a/t/t4067-diff-partial-clone.sh b/t/t4067-diff-partial-clone.sh
> new file mode 100755

Also: thank you very much for introducing this test script, to make sure
that things work as expected. Without it, we would not have detected any
regression wrt multi-promisor.

This iteration looks good to me, thank you so much!
Dscho

> index 0000000000..349851be7d
> --- /dev/null
> +++ b/t/t4067-diff-partial-clone.sh
> @@ -0,0 +1,103 @@
> +#!/bin/sh
> +
> +test_description='behavior of diff when reading objects in a partial clone'
> +
> +. ./test-lib.sh
> +
> +test_expect_success 'git show batches blobs' '
> +	test_when_finished "rm -rf server client trace" &&
> +
> +	test_create_repo server &&
> +	echo a >server/a &&
> +	echo b >server/b &&
> +	git -C server add a b &&
> +	git -C server commit -m x &&
> +
> +	test_config -C server uploadpack.allowfilter 1 &&
> +	test_config -C server uploadpack.allowanysha1inwant 1 &&
> +	git clone --bare --filter=blob:limit=0 "file://$(pwd)/server" client &&
> +
> +	# Ensure that there is exactly 1 negotiation by checking that there is
> +	# only 1 "done" line sent. ("done" marks the end of negotiation.)
> +	GIT_TRACE_PACKET="$(pwd)/trace" git -C client show HEAD &&
> +	grep "git> done" trace >done_lines &&
> +	test_line_count = 1 done_lines
> +'
> +
> +test_expect_success 'diff batches blobs' '
> +	test_when_finished "rm -rf server client trace" &&
> +
> +	test_create_repo server &&
> +	echo a >server/a &&
> +	echo b >server/b &&
> +	git -C server add a b &&
> +	git -C server commit -m x &&
> +	echo c >server/c &&
> +	echo d >server/d &&
> +	git -C server add c d &&
> +	git -C server commit -m x &&
> +
> +	test_config -C server uploadpack.allowfilter 1 &&
> +	test_config -C server uploadpack.allowanysha1inwant 1 &&
> +	git clone --bare --filter=blob:limit=0 "file://$(pwd)/server" client &&
> +
> +	# Ensure that there is exactly 1 negotiation by checking that there is
> +	# only 1 "done" line sent. ("done" marks the end of negotiation.)
> +	GIT_TRACE_PACKET="$(pwd)/trace" git -C client diff HEAD^ HEAD &&
> +	grep "git> done" trace >done_lines &&
> +	test_line_count = 1 done_lines
> +'
> +
> +test_expect_success 'diff skips same-OID blobs' '
> +	test_when_finished "rm -rf server client trace" &&
> +
> +	test_create_repo server &&
> +	echo a >server/a &&
> +	echo b >server/b &&
> +	git -C server add a b &&
> +	git -C server commit -m x &&
> +	echo another-a >server/a &&
> +	git -C server add a &&
> +	git -C server commit -m x &&
> +
> +	test_config -C server uploadpack.allowfilter 1 &&
> +	test_config -C server uploadpack.allowanysha1inwant 1 &&
> +	git clone --bare --filter=blob:limit=0 "file://$(pwd)/server" client &&
> +
> +	echo a | git hash-object --stdin >hash-old-a &&
> +	echo another-a | git hash-object --stdin >hash-new-a &&
> +	echo b | git hash-object --stdin >hash-b &&
> +
> +	# Ensure that only a and another-a are fetched.
> +	GIT_TRACE_PACKET="$(pwd)/trace" git -C client diff HEAD^ HEAD &&
> +	grep "want $(cat hash-old-a)" trace &&
> +	grep "want $(cat hash-new-a)" trace &&
> +	! grep "want $(cat hash-b)" trace
> +'
> +
> +test_expect_success 'diff with rename detection batches blobs' '
> +	test_when_finished "rm -rf server client trace" &&
> +
> +	test_create_repo server &&
> +	echo a >server/a &&
> +	printf "b\nb\nb\nb\nb\n" >server/b &&
> +	git -C server add a b &&
> +	git -C server commit -m x &&
> +	rm server/b &&
> +	printf "b\nb\nb\nb\nbX\n" >server/c &&
> +	git -C server add c &&
> +	git -C server commit -a -m x &&
> +
> +	test_config -C server uploadpack.allowfilter 1 &&
> +	test_config -C server uploadpack.allowanysha1inwant 1 &&
> +	git clone --bare --filter=blob:limit=0 "file://$(pwd)/server" client &&
> +
> +	# Ensure that there is exactly 1 negotiation by checking that there is
> +	# only 1 "done" line sent. ("done" marks the end of negotiation.)
> +	GIT_TRACE_PACKET="$(pwd)/trace" git -C client diff -M HEAD^ HEAD >out &&
> +	grep "similarity index" out &&
> +	grep "git> done" trace >done_lines &&
> +	test_line_count = 1 done_lines
> +'
> +
> +test_done
> --
> 2.21.0.197.gd478713db0
>
>