path: root/builtin/cat-file.c
diff options
authorJeff King <>2013-07-12 06:20:05 (GMT)
committerJunio C Hamano <>2013-07-12 17:09:56 (GMT)
commit25fba78d36be6297bb17aed5f3e21ed850ce3e03 (patch)
tree4f1d4e1685ed7c3ce591b60aa9bd15a5976ef233 /builtin/cat-file.c
parentee6e5843c11ca5cba0d5ce964325a3b529299e0d (diff)
cat-file: disable object/refname ambiguity check for batch mode
A common use of "cat-file --batch-check" is to feed a list of objects from "rev-list --objects" or a similar command. In this instance, all of our input objects are 40-byte sha1 ids. However, cat-file has always allowed arbitrary revision specifiers, and feeds the result to get_sha1(). Fortunately, get_sha1() recognizes a 40-byte sha1 before doing any hard work trying to look up refs, meaning this scenario should end up spending very little time converting the input into an object sha1. However, since 798c35f (get_sha1: warn about full or short object names that look like refs, 2013-05-29), when we encounter this case, we spend the extra effort to do a refname lookup anyway, just to print a warning. This is further exacerbated by ca91993 (get_packed_ref_cache: reload packed-refs file when it changes, 2013-06-20), which makes individual ref lookup more expensive by requiring a stat() of the packed-refs file for each missing ref. With no patches, this is the time it takes to run: $ git rev-list --objects --all >objects $ time git cat-file --batch-check='%(objectname)' <objects on the linux.git repository: real 1m13.494s user 0m25.924s sys 0m47.532s If we revert ca91993, the packed-refs up-to-date check, it gets a little better: real 0m54.697s user 0m21.692s sys 0m32.916s but we are still spending quite a bit of time on ref lookup (and we would not want to revert that patch, anyway, which has correctness issues). If we revert 798c35f, disabling the warning entirely, we get a much more reasonable time: real 0m7.452s user 0m6.836s sys 0m0.608s This patch does the moral equivalent of this final case (and gets similar speedups). We introduce a global flag that callers of get_sha1() can use to avoid paying the price for the warning. Signed-off-by: Jeff King <> Signed-off-by: Junio C Hamano <>
Diffstat (limited to 'builtin/cat-file.c')
1 files changed, 9 insertions, 0 deletions
diff --git a/builtin/cat-file.c b/builtin/cat-file.c
index 0e64b41..fe5c77f 100644
--- a/builtin/cat-file.c
+++ b/builtin/cat-file.c
@@ -266,6 +266,15 @@ static int batch_objects(struct batch_options *opt)
strbuf_expand(&buf, opt->format, expand_format, &data);
data.mark_query = 0;
+ /*
+ * We are going to call get_sha1 on a potentially very large number of
+ * objects. In most large cases, these will be actual object sha1s. The
+ * cost to double-check that each one is not also a ref (just so we can
+ * warn) ends up dwarfing the actual cost of the object lookups
+ * themselves. We can work around it by just turning off the warning.
+ */
+ warn_on_object_refname_ambiguity = 0;
while (strbuf_getline(&buf, stdin, '\n') != EOF) {
char *p;
int error;