Re: [RFC PATCH] diff: only prefetch for certain output formats
- From
Jeff King <peff@peff.net>
- Date
- Jan 30, 2020, 05:51 UTC
- Message-ID
- <20200130055136.GA2184413@coredump.intra.peff.net>
- In-Reply-To
- <20200130013900.181477-1-jonathantanmy@google.com>
On Wed, Jan 29, 2020 at 05:39:00PM -0800, Jonathan Tan wrote:
Show 25 quoted lines
> > You could get pretty specific by putting logic inside diffcore_rename(), > > which would know if anything is left over after exact rename detection, > > but I suspect just checking: > > > > (options->break_opt != -1 || options->detect_rename) > > > > in diffcore_std() would be OK in practice. > > Thanks for taking a look at this patch and for the pointers, especially > to rename detection. I investigated and found that in practice, with > respect to rename detection, options->detect_rename is insufficient to > determine exactly when we need to fetch; we need to fetch when > (for example) a file is deleted and another added, but not when a file > is merely changed, and these rules are not reflected in > options->detect_rename. These rules indeed are in diffcore_rename(), as > you mentioned, but putting logic inside diffcore_rename() (or copying > the same logic over to diffcore_std()) complicates things for too little > benefit, I think. > > To add to this, rename detection is turned on by default, so it wouldn't > even fix the original issue with "status". > > So I'll abandon this patch, at least until someone finds a use case for > diffing with no rename detection on a partial clone and would rather not > have a prefetch.
Ah, true, "options->detect_rename" would be overly broad.
I actually don't think it would be that bad to put the logic in diffcore_rename(). If we wait until the right moment (after inexact renames have been resolved, and when we see if there are any candidates left), it should just be a matter of walking over the candidate lists.
Something like this (it would need the add_if_missing() helper from diffcore_std()):
diff --git a/diffcore-rename.c b/diffcore-rename.c index 531d7adeaf..d519ffcc45 100644 --- a/diffcore-rename.c +++ b/diffcore-rename.c @@ -458,6 +458,7 @@ void diffcore_rename(struct diff_options *options) int i, j, rename_count, skip_unmodified = 0; int num_create, dst_cnt; struct progress *progress = NULL; + struct oid_array to_fetch = OID_ARRAY_INIT; if (!minimum_score) minimum_score = DEFAULT_RENAME_SCORE; @@ -538,6 +539,25 @@ void diffcore_rename(struct diff_options *options) break; } + /* + * At this point we know there's actual work to do: we have rename + * destinations that didn't find an exact match, and we have potential + * sources. So we'll have to do inexact rename detection, which + * requires looking at the blobs. It's worth pre-fetching them as a + * group now. + */ + for (i = 0; i < rename_dst_nr; i++) { + if (rename_dst[i].pair) + continue; /* already found exact match */ + add_if_missing(options->repo, &to_fetch, rename_dst[i].two); + } + for (i = 0; i < rename_src_nr; i++) { + add_if_missing(options->repo, &to_fetch, rename_src[i].p->one); + } + if (to_fetch.nr) + promisor_remote_get_direct(options->repo, + to_fetch.oid, to_fetch.nr); + if (options->show_rename_progress) { progress = start_delayed_progress( _("Performing inexact rename detection"),