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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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12
diffcore-break.c
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@ -4,6 +4,7 @@
#include "cache.h"
#include "diff.h"
#include "diffcore.h"
#include "promisor-remote.h"
static int should_break(struct repository *r,
struct diff_filespec *src,
@ -49,6 +50,8 @@ static int should_break(struct repository *r,
unsigned long delta_size, max_size;
unsigned long src_copied, literal_added, src_removed;
struct diff_populate_filespec_options options = { 0 };
*merge_score_p = 0; /* assume no deletion --- "do not break"
* is the default.
*/
@ -62,8 +65,13 @@ static int should_break(struct repository *r,
oideq(&src->oid, &dst->oid))
return 0; /* they are the same */
if (diff_populate_filespec(r, src, NULL) ||
diff_populate_filespec(r, dst, NULL))
if (r == the_repository && has_promisor_remote()) {
options.missing_object_cb = diff_queued_diff_prefetch;
options.missing_object_data = r;
}
if (diff_populate_filespec(r, src, &options) ||
diff_populate_filespec(r, dst, &options))
return 0; /* error but caught downstream */
max_size = ((src->size > dst->size) ? src->size : dst->size);