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author | Patrick Steinhardt <ps@pks.im> | 2022-03-01 09:33:54 (GMT) |
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committer | Junio C Hamano <gitster@pobox.com> | 2022-03-01 18:13:46 (GMT) |
commit | 0a7b38707d5d5c8a7baeb88a85d6259cee4f4e4d (patch) | |
tree | c233e2c2ba016d8e3b21389290eedec7aad4ec0c /refs/files-backend.c | |
parent | 1553f5e76c72243f61b454412b651706a869388f (diff) | |
download | git-0a7b38707d5d5c8a7baeb88a85d6259cee4f4e4d.zip git-0a7b38707d5d5c8a7baeb88a85d6259cee4f4e4d.tar.gz git-0a7b38707d5d5c8a7baeb88a85d6259cee4f4e4d.tar.bz2 |
refs/files-backend: optimize reading of symbolic refs
When reading references via `files_read_raw_ref()` we always consult
both the loose reference, and if that wasn't found, we also consult the
packed-refs file. While this makes sense to read a generic reference, it
is wasteful in the case where we only care about symbolic references:
the packed-refs backend does not support them, and thus it cannot ever
return one for us.
Special-case reading of symbolic references for the files backend such
that we always skip asking the packed-refs backend.
We use `refs_read_symbolic_ref()` extensively to determine whether we
need to skip updating local symbolic references during a fetch, which is
why the change results in a significant speedup when doing fetches in
repositories with huge numbers of references. The following benchmark
executes a mirror-fetch in a repository with about 2 million references
via `git fetch --prune --no-write-fetch-head +refs/*:refs/*`:
Benchmark 1: HEAD~
Time (mean ± σ): 68.372 s ± 2.344 s [User: 65.629 s, System: 8.786 s]
Range (min … max): 65.745 s … 70.246 s 3 runs
Benchmark 2: HEAD
Time (mean ± σ): 60.259 s ± 0.343 s [User: 61.019 s, System: 7.245 s]
Range (min … max): 60.003 s … 60.649 s 3 runs
Summary
'HEAD' ran
1.13 ± 0.04 times faster than 'HEAD~'
Signed-off-by: Patrick Steinhardt <ps@pks.im>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
Diffstat (limited to 'refs/files-backend.c')
-rw-r--r-- | refs/files-backend.c | 34 |
1 files changed, 28 insertions, 6 deletions
diff --git a/refs/files-backend.c b/refs/files-backend.c index f3428a9..0457ecd 100644 --- a/refs/files-backend.c +++ b/refs/files-backend.c @@ -338,9 +338,9 @@ static struct ref_cache *get_loose_ref_cache(struct files_ref_store *refs) return refs->loose; } -static int files_read_raw_ref(struct ref_store *ref_store, const char *refname, - struct object_id *oid, struct strbuf *referent, - unsigned int *type, int *failure_errno) +static int read_ref_internal(struct ref_store *ref_store, const char *refname, + struct object_id *oid, struct strbuf *referent, + unsigned int *type, int *failure_errno, int skip_packed_refs) { struct files_ref_store *refs = files_downcast(ref_store, REF_STORE_READ, "read_raw_ref"); @@ -381,7 +381,7 @@ stat_ref: if (lstat(path, &st) < 0) { int ignore_errno; myerr = errno; - if (myerr != ENOENT) + if (myerr != ENOENT || skip_packed_refs) goto out; if (refs_read_raw_ref(refs->packed_ref_store, refname, oid, referent, type, &ignore_errno)) { @@ -425,7 +425,8 @@ stat_ref: * ref is supposed to be, there could still be a * packed ref: */ - if (refs_read_raw_ref(refs->packed_ref_store, refname, oid, + if (skip_packed_refs || + refs_read_raw_ref(refs->packed_ref_store, refname, oid, referent, type, &ignore_errno)) { myerr = EISDIR; goto out; @@ -470,6 +471,27 @@ out: return ret; } +static int files_read_raw_ref(struct ref_store *ref_store, const char *refname, + struct object_id *oid, struct strbuf *referent, + unsigned int *type, int *failure_errno) +{ + return read_ref_internal(ref_store, refname, oid, referent, type, failure_errno, 0); +} + +static int files_read_symbolic_ref(struct ref_store *ref_store, const char *refname, + struct strbuf *referent) +{ + struct object_id oid; + int failure_errno, ret; + unsigned int type; + + ret = read_ref_internal(ref_store, refname, &oid, referent, &type, &failure_errno, 1); + if (ret) + return ret; + + return !(type & REF_ISSYMREF); +} + int parse_loose_ref_contents(const char *buf, struct object_id *oid, struct strbuf *referent, unsigned int *type, int *failure_errno) @@ -3286,7 +3308,7 @@ struct ref_storage_be refs_be_files = { files_ref_iterator_begin, files_read_raw_ref, - NULL, + files_read_symbolic_ref, files_reflog_iterator_begin, files_for_each_reflog_ent, |