sha1_file: only freshen packs once per run

Since 33d4221 (write_sha1_file: freshen existing objects,
2014-10-15), we update the mtime of existing objects that we
would have written out (had they not existed). For the
common case in which many objects are packed, we may update
the mtime on a single packfile repeatedly. This can result
in a noticeable performance problem if calling utime() is
expensive (e.g., because your storage is on NFS).

We can fix this by keeping a per-pack flag that lets us
freshen only once per program invocation.

An alternative would be to keep the packed_git.mtime flag up
to date as we freshen, and freshen only once every N
seconds. In practice, it's not worth the complexity. We are
racing against prune expiration times here, which inherently
must be set to accomodate reasonable program running times
(because they really care about the time between an object
being written and it becoming referenced, and the latter is
typically the last step a program takes).

Signed-off-by: Jeff King <peff@peff.net>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

diff --git a/cache.h b/cache.h
index c7565f6acb34f741ca78dda62e3afa5546dc5be2..e9178333918411771e308a84dff6a8406570ad54 100644 (file)
--- a/cache.h
+++ b/cache.h
@@ -1168,6 +1168,7 @@ extern struct packed_git {
        int pack_fd;
        unsigned pack_local:1,
                 pack_keep:1,
+                freshened:1,
                 do_not_close:1;
        unsigned char sha1[20];
        /* something like ".git/objects/pack/xxxxx.pack" */

diff --git a/sha1_file.c b/sha1_file.c
index cd6c102ccfdcc43e29ead7a07300d5ae18fca2ab..bf1bdbcdf5e4f20c58c338decbaa7506d02c3217 100644 (file)
--- a/sha1_file.c
+++ b/sha1_file.c
@@ -2999,7 +2999,14 @@ static int freshen_loose_object(const unsigned char *sha1)
 static int freshen_packed_object(const unsigned char *sha1)
 {
        struct pack_entry e;
-       return find_pack_entry(sha1, &e) && freshen_file(e.p->pack_name);
+       if (!find_pack_entry(sha1, &e))
+               return 0;
+       if (e.p->freshened)
+               return 1;
+       if (!freshen_file(e.p->pack_name))
+               return 0;
+       e.p->freshened = 1;
+       return 1;
 }
 
 int write_sha1_file(const void *buf, unsigned long len, const char *type, unsigned char *returnsha1)