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refs: write packed_refs file using stdio 

We write each line of a new packed-refs file individually
using a write() syscall (and sometimes 2, if the ref is
peeled). Since each line is only about 50-100 bytes long,
this creates a lot of system call overhead.

We can instead open a stdio handle around our descriptor and
use fprintf to write to it. The extra buffering is not a
problem for us, because nobody will read our new packed-refs
file until we call commit_lock_file (by which point we have
flushed everything).

On a pathological repository with 8.5 million refs, this
dropped the time to run `git pack-refs` from 20s to 6s.

Signed-off-by: Jeff King <peff@peff.net>
Reviewed-by: Michael Haggerty <mhagger@alum.mit.edu>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
This commit is contained in:
Jeff King 2014-09-10 06:03:52 -04:00 committed by Junio C Hamano
parent 0c72b98f31
commit 9540ce5030
3 changed files with 33 additions and 23 deletions
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2
cache.h
View File

@ -1395,6 +1395,8 @@ extern const char *git_mailmap_blob;
/* IO helper functions */
extern void maybe_flush_or_die(FILE *, const char *);
__attribute__((format (printf, 2, 3)))
extern void fprintf_or_die(FILE *, const char *fmt, ...);
extern int copy_fd(int ifd, int ofd);
extern int copy_file(const char *dst, const char *src, int mode);
extern int copy_file_with_time(const char *dst, const char *src, int mode);

39
refs.c
View File

@ -2191,25 +2191,12 @@ struct ref_lock *lock_any_ref_for_update(const char *refname,
* Write an entry to the packed-refs file for the specified refname.
* If peeled is non-NULL, write it as the entry's peeled value.
*/
static void write_packed_entry(int fd, char *refname, unsigned char *sha1,
static void write_packed_entry(FILE *fh, char *refname, unsigned char *sha1,
unsigned char *peeled)
{
char line[PATH_MAX + 100];
int len;
len = snprintf(line, sizeof(line), "%s %s\n",
sha1_to_hex(sha1), refname);
/* this should not happen but just being defensive */
if (len > sizeof(line))
die("too long a refname '%s'", refname);
write_or_die(fd, line, len);
if (peeled) {
if (snprintf(line, sizeof(line), "^%s\n",
sha1_to_hex(peeled)) != PEELED_LINE_LENGTH)
die("internal error");
write_or_die(fd, line, PEELED_LINE_LENGTH);
}
fprintf_or_die(fh, "%s %s\n", sha1_to_hex(sha1), refname);
if (peeled)
fprintf_or_die(fh, "^%s\n", sha1_to_hex(peeled));
}
/*
@ -2217,13 +2204,12 @@ static void write_packed_entry(int fd, char *refname, unsigned char *sha1,
*/
static int write_packed_entry_fn(struct ref_entry *entry, void *cb_data)
{
int *fd = cb_data;
enum peel_status peel_status = peel_entry(entry, 0);
if (peel_status != PEEL_PEELED && peel_status != PEEL_NON_TAG)
error("internal error: %s is not a valid packed reference!",
entry->name);
write_packed_entry(*fd, entry->name, entry->u.value.sha1,
write_packed_entry(cb_data, entry->name, entry->u.value.sha1,
peel_status == PEEL_PEELED ?
entry->u.value.peeled : NULL);
return 0;
@ -2259,15 +2245,22 @@ int commit_packed_refs(void)
get_packed_ref_cache(&ref_cache);
int error = 0;
int save_errno = 0;
FILE *out;
if (!packed_ref_cache->lock)
die("internal error: packed-refs not locked");
write_or_die(packed_ref_cache->lock->fd,
PACKED_REFS_HEADER, strlen(PACKED_REFS_HEADER));
out = fdopen(packed_ref_cache->lock->fd, "w");
if (!out)
die_errno("unable to fdopen packed-refs descriptor");
fprintf_or_die(out, "%s", PACKED_REFS_HEADER);
do_for_each_entry_in_dir(get_packed_ref_dir(packed_ref_cache),
0, write_packed_entry_fn,
&packed_ref_cache->lock->fd);
0, write_packed_entry_fn, out);
if (fclose(out))
die_errno("write error");
packed_ref_cache->lock->fd = -1;
if (commit_lock_file(packed_ref_cache->lock)) {
save_errno = errno;
error = -1;

15
write_or_die.c
View File

@ -49,6 +49,21 @@ void maybe_flush_or_die(FILE *f, const char *desc)
}
}
void fprintf_or_die(FILE *f, const char *fmt, ...)
{
va_list ap;
int ret;
va_start(ap, fmt);
ret = vfprintf(f, fmt, ap);
va_end(ap);
if (ret < 0) {
check_pipe(errno);
die_errno("write error");
}
}
void fsync_or_die(int fd, const char *msg)
{
if (fsync(fd) < 0) {