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diff: restrict when prefetching occurs

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Commit 7fbbcb21b1 ("diff: batch fetching of missing blobs", 2019-04-08)
optimized "diff" by prefetching blobs in a partial clone, but there are
some cases wherein blobs do not need to be prefetched. In these cases,
any command that uses the diff machinery will unnecessarily fetch blobs.

diffcore_std() may read blobs when it calls the following functions:
 (1) diffcore_skip_stat_unmatch() (controlled by the config variable
     diff.autorefreshindex)
 (2) diffcore_break() and diffcore_merge_broken() (for break-rewrite
     detection)
 (3) diffcore_rename() (for rename detection)
 (4) diffcore_pickaxe() (for detecting addition/deletion of specified
     string)

Instead of always prefetching blobs, teach diffcore_skip_stat_unmatch(),
diffcore_break(), and diffcore_rename() to prefetch blobs upon the first
read of a missing object. This covers (1), (2), and (3): to cover the
rest, teach diffcore_std() to prefetch if the output type is one that
includes blob data (and hence blob data will be required later anyway),
or if it knows that (4) will be run.

Helped-by: Jeff King <peff@peff.net>
Signed-off-by: Jonathan Tan <jonathantanmy@google.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
This commit is contained in:
Jonathan Tan
2020-04-07 15:11:43 -07:00
committed by Junio C Hamano
parent c14b6f83ec
commit 95acf11a3d
5 changed files with 181 additions and 28 deletions
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55
diffcore-rename.c
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@ -1,4 +1,5 @@
/*
*
* Copyright (C) 2005 Junio C Hamano
*/
#include "cache.h"
@ -7,6 +8,7 @@
#include "object-store.h"
#include "hashmap.h"
#include "progress.h"
#include "promisor-remote.h"
/* Table of rename/copy destinations */
@ -128,10 +130,46 @@ struct diff_score {
short name_score;
};
struct prefetch_options {
struct repository *repo;
int skip_unmodified;
};
static void prefetch(void *prefetch_options)
{
struct prefetch_options *options = prefetch_options;
int i;
struct oid_array to_fetch = OID_ARRAY_INIT;
for (i = 0; i < rename_dst_nr; i++) {
if (rename_dst[i].pair)
/*
* The loop in diffcore_rename() will not need these
* blobs, so skip prefetching.
*/
continue; /* already found exact match */
diff_add_if_missing(options->repo, &to_fetch,
rename_dst[i].two);
}
for (i = 0; i < rename_src_nr; i++) {
if (options->skip_unmodified &&
diff_unmodified_pair(rename_src[i].p))
/*
* The loop in diffcore_rename() will not need these
* blobs, so skip prefetching.
*/
continue;
diff_add_if_missing(options->repo, &to_fetch,
rename_src[i].p->one);
}
promisor_remote_get_direct(options->repo, to_fetch.oid, to_fetch.nr);
oid_array_clear(&to_fetch);
}
static int estimate_similarity(struct repository *r,
struct diff_filespec *src,
struct diff_filespec *dst,
int minimum_score)
int minimum_score,
int skip_unmodified)
{
/* src points at a file that existed in the original tree (or
* optionally a file in the destination tree) and dst points
@ -151,6 +189,12 @@ static int estimate_similarity(struct repository *r,
struct diff_populate_filespec_options dpf_options = {
.check_size_only = 1
};
struct prefetch_options prefetch_options = {r, skip_unmodified};
if (r == the_repository && has_promisor_remote()) {
dpf_options.missing_object_cb = prefetch;
dpf_options.missing_object_data = &prefetch_options;
}
/* We deal only with regular files. Symlink renames are handled
* only when they are exact matches --- in other words, no edits
@ -190,9 +234,11 @@ static int estimate_similarity(struct repository *r,
if (max_size * (MAX_SCORE-minimum_score) < delta_size * MAX_SCORE)
return 0;
if (!src->cnt_data && diff_populate_filespec(r, src, NULL))
dpf_options.check_size_only = 0;
if (!src->cnt_data && diff_populate_filespec(r, src, &dpf_options))
return 0;
if (!dst->cnt_data && diff_populate_filespec(r, dst, NULL))
if (!dst->cnt_data && diff_populate_filespec(r, dst, &dpf_options))
return 0;
if (diffcore_count_changes(r, src, dst,
@ -569,7 +615,8 @@ void diffcore_rename(struct diff_options *options)
this_src.score = estimate_similarity(options->repo,
one, two,
minimum_score);
minimum_score,
skip_unmodified);
this_src.name_score = basename_same(one, two);
this_src.dst = i;
this_src.src = j;