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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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21
diffcore.h
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@ -65,9 +65,22 @@ void free_filespec(struct diff_filespec *);
void fill_filespec(struct diff_filespec *, const struct object_id *,
int, unsigned short);
/*
* Prefetch the entries in diff_queued_diff. The parameter is a pointer to a
* struct repository.
*/
void diff_queued_diff_prefetch(void *repository);
struct diff_populate_filespec_options {
unsigned check_size_only : 1;
unsigned check_binary : 1;
/*
* If an object is missing, diff_populate_filespec() will invoke this
* callback before attempting to read that object again.
*/
void (*missing_object_cb)(void *);
void *missing_object_data;
};
int diff_populate_filespec(struct repository *, struct diff_filespec *,
const struct diff_populate_filespec_options *);
@ -185,4 +198,12 @@ int diffcore_count_changes(struct repository *r,
unsigned long *src_copied,
unsigned long *literal_added);
/*
* If filespec contains an OID and if that object is missing from the given
* repository, add that OID to to_fetch.
*/
void diff_add_if_missing(struct repository *r,
struct oid_array *to_fetch,
const struct diff_filespec *filespec);
#endif