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speed up alt_odb_usable() with many alternates

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With many alternates, the duplicate check in alt_odb_usable()
wastes many cycles doing repeated fspathcmp() on every existing
alternate.  Use a khash to speed up lookups by odb->path.

Since the kh_put_* API uses the supplied key without
duplicating it, we also take advantage of it to replace both
xstrdup() and strbuf_release() in link_alt_odb_entry() with
strbuf_detach() to avoid the allocation and copy.

In a test repository with 50K alternates and each of those 50K
alternates having one alternate each (for a total of 100K total
alternates); this speeds up lookup of a non-existent blob from
over 16 minutes to roughly 2.7 seconds on my busy workstation.

Note: all underlying git object directories were small and
unpacked with only loose objects and no packs.  Having to load
packs increases times significantly.

Signed-off-by: Eric Wong <e@80x24.org>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
This commit is contained in:
Eric Wong
2021-07-07 23:10:15 +00:00
committed by Junio C Hamano
parent 670b81a890
commit cf2dc1c238
5 changed files with 43 additions and 13 deletions
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2
dir.h
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@@ -489,7 +489,9 @@ int remove_dir_recursively(struct strbuf *path, int flag);
int remove_path(const char *path);
int fspathcmp(const char *a, const char *b);
int fspatheq(const char *a, const char *b);
int fspathncmp(const char *a, const char *b, size_t count);
unsigned int fspathhash(const char *str);
/*
* The prefix part of pattern must not contains wildcards.