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peel_ref: check object type before loading
The point of peel_ref is to dereference tags; if the base object is not a tag, then we can return early without even loading the object into memory. This patch accomplishes that by checking sha1_object_info for the type. For a packed object, we can get away with just looking in the pack index. For a loose object, we only need to inflate the first couple of header bytes. This is a bit of a gamble; if we do find a tag object, then we will end up loading the content anyway, and the extra lookup will have been wasteful. However, if it is not a tag object, then we save loading the object entirely. Depending on the ratio of non-tags to tags in the input, this can be a minor win or minor loss. However, it does give us one potential major win: if a ref points to a large blob (e.g., via an unannotated tag), then we can avoid looking at it entirely. Signed-off-by: Jeff King <peff@peff.net> Signed-off-by: Junio C Hamano <gitster@pobox.com>
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refs.c
11
refs.c
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@ -1225,8 +1225,15 @@ int peel_ref(const char *refname, unsigned char *sha1)
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}
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fallback:
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o = parse_object(base);
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if (o && o->type == OBJ_TAG) {
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o = lookup_unknown_object(base);
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if (o->type == OBJ_NONE) {
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int type = sha1_object_info(base, NULL);
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if (type < 0)
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return -1;
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o->type = type;
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}
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if (o->type == OBJ_TAG) {
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o = deref_tag_noverify(o);
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if (o) {
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hashcpy(sha1, o->sha1);
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