From: Elijah Newren Date: Thu, 14 May 2026 16:25:27 +0000 (+0000) Subject: builtin/log: prefetch necessary blobs for `git cherry` X-Git-Tag: v2.55.0-rc0~52^2~1 X-Git-Url: http://git.ipfire.org/cgi-bin/gitweb.cgi?a=commitdiff_plain;h=463c1bfc2b65357569055916e348e1bd9c7a5b25;p=thirdparty%2Fgit.git builtin/log: prefetch necessary blobs for `git cherry` In partial clones, `git cherry` fetches necessary blobs on-demand one at a time, which can be very slow. We would like to prefetch all necessary blobs upfront. To do so, we need to be able to first figure out which blobs are needed. `git cherry` does its work in a two-phase approach: first computing header-only IDs (based on file paths and modes), then falling back to full content-based IDs only when header-only IDs collide -- or, more accurately, whenever the oidhash() of the header-only object_ids collide. patch-ids.c handles this by creating an ids->patches hashmap that has all the data we need, but the problem is that any attempt to query the hashmap will invoke the patch_id_neq() function on any colliding objects, which causes the on-demand fetching. Insert a new prefetch_cherry_blobs() function before checking for collisions. Use a temporary replacement on the ids->patches.cmpfn in order to enumerate the blobs that would be needed without yet fetching them, and then fetch them all at once, then restore the old ids->patches.cmpfn. Signed-off-by: Elijah Newren Signed-off-by: Junio C Hamano --- diff --git a/builtin/log.c b/builtin/log.c index 8c0939dd42..e464b30af4 100644 --- a/builtin/log.c +++ b/builtin/log.c @@ -21,10 +21,12 @@ #include "color.h" #include "commit.h" #include "diff.h" +#include "diffcore.h" #include "diff-merges.h" #include "revision.h" #include "log-tree.h" #include "oid-array.h" +#include "oidset.h" #include "tag.h" #include "reflog-walk.h" #include "patch-ids.h" @@ -43,9 +45,11 @@ #include "utf8.h" #include "commit-reach.h" +#include "promisor-remote.h" #include "range-diff.h" #include "tmp-objdir.h" #include "tree.h" +#include "userdiff.h" #include "write-or-die.h" #define MAIL_DEFAULT_WRAP 72 @@ -2602,6 +2606,131 @@ static void print_commit(char sign, struct commit *commit, int verbose, } } +/* + * Enumerate blob OIDs from a single commit's diff, inserting them into blobs. + * Skips files whose userdiff driver explicitly declares binary status + * (drv->binary > 0), since patch-ID uses oid_to_hex() for those and + * never reads blob content. Use userdiff_find_by_path() since + * diff_filespec_load_driver() is static in diff.c. + * + * Clean up with diff_queue_clear() (from diffcore.h). + */ +static void collect_diff_blob_oids(struct commit *commit, + struct diff_options *opts, + struct oidset *blobs) +{ + struct diff_queue_struct *q; + + /* + * Merge commits are filtered out by patch_id_defined() in patch-ids.c, + * so we'll never be called with one. + */ + assert(!commit->parents || !commit->parents->next); + + if (commit->parents) + diff_tree_oid(&commit->parents->item->object.oid, + &commit->object.oid, "", opts); + else + diff_root_tree_oid(&commit->object.oid, "", opts); + diffcore_std(opts); + + q = &diff_queued_diff; + for (int i = 0; i < q->nr; i++) { + struct diff_filepair *p = q->queue[i]; + struct userdiff_driver *drv; + + /* Skip binary files */ + drv = userdiff_find_by_path(opts->repo->index, p->one->path); + if (drv && drv->binary > 0) + continue; + + if (DIFF_FILE_VALID(p->one) && + odb_read_object_info_extended(opts->repo->objects, + &p->one->oid, NULL, + OBJECT_INFO_FOR_PREFETCH)) + oidset_insert(blobs, &p->one->oid); + if (DIFF_FILE_VALID(p->two) && + odb_read_object_info_extended(opts->repo->objects, + &p->two->oid, NULL, + OBJECT_INFO_FOR_PREFETCH)) + oidset_insert(blobs, &p->two->oid); + } + diff_queue_clear(q); +} + +static int always_match(const void *cmp_data UNUSED, + const struct hashmap_entry *entry1 UNUSED, + const struct hashmap_entry *entry2 UNUSED, + const void *keydata UNUSED) +{ + return 0; +} + +/* + * Prefetch blobs for git cherry in partial clones. + * + * Called between the revision walk (which builds the head-side + * commit list) and the has_commit_patch_id() comparison loop. + * + * Uses a cmpfn-swap trick to avoid reading blobs: temporarily + * replaces the hashmap's comparison function with a trivial + * always-match function, so hashmap_get()/hashmap_get_next() match + * any entry with the same oidhash bucket. These are the set of oids + * that would trigger patch_id_neq() during normal lookup and cause + * blobs to be read on demand, and we want to prefetch them all at + * once instead. + */ +static void prefetch_cherry_blobs(struct repository *repo, + struct commit_list *list, + struct patch_ids *ids) +{ + struct oidset blobs = OIDSET_INIT; + hashmap_cmp_fn original_cmpfn; + + /* Exit if we're not in a partial clone */ + if (!repo_has_promisor_remote(repo)) + return; + + /* Save original cmpfn, replace with always_match */ + original_cmpfn = ids->patches.cmpfn; + ids->patches.cmpfn = always_match; + + /* Find header-only collisions, gather blobs from those commits */ + for (struct commit_list *l = list; l; l = l->next) { + struct commit *c = l->item; + bool match_found = false; + for (struct patch_id *cur = patch_id_iter_first(c, ids); + cur; + cur = patch_id_iter_next(cur, ids)) { + match_found = true; + collect_diff_blob_oids(cur->commit, &ids->diffopts, + &blobs); + } + if (match_found) + collect_diff_blob_oids(c, &ids->diffopts, &blobs); + } + + /* Restore original cmpfn */ + ids->patches.cmpfn = original_cmpfn; + + /* If we have any blobs to fetch, fetch them */ + if (oidset_size(&blobs)) { + struct oid_array to_fetch = OID_ARRAY_INIT; + struct oidset_iter iter; + const struct object_id *oid; + + oidset_iter_init(&blobs, &iter); + while ((oid = oidset_iter_next(&iter))) + oid_array_append(&to_fetch, oid); + + promisor_remote_get_direct(repo, to_fetch.oid, to_fetch.nr); + + oid_array_clear(&to_fetch); + } + + oidset_clear(&blobs); +} + int cmd_cherry(int argc, const char **argv, const char *prefix, @@ -2673,6 +2802,8 @@ int cmd_cherry(int argc, commit_list_insert(commit, &list); } + prefetch_cherry_blobs(the_repository, list, &ids); + for (struct commit_list *l = list; l; l = l->next) { char sign = '+'; diff --git a/t/t3500-cherry.sh b/t/t3500-cherry.sh index 78c3eac54b..3e66827d76 100755 --- a/t/t3500-cherry.sh +++ b/t/t3500-cherry.sh @@ -78,4 +78,31 @@ test_expect_success 'cherry ignores whitespace' ' test_cmp expect actual ' +# Reuse the expect file from the previous test, in a partial clone +test_expect_success 'cherry in partial clone does bulk prefetch' ' + test_config uploadpack.allowfilter 1 && + test_config uploadpack.allowanysha1inwant 1 && + test_when_finished "rm -rf copy" && + + git clone --bare --filter=blob:none file://"$(pwd)" copy && + ( + cd copy && + GIT_TRACE2_EVENT="$(pwd)/trace.output" git cherry upstream-with-space feature-without-space >actual && + test_cmp ../expect actual && + + grep "child_start.*fetch.negotiationAlgorithm" trace.output >fetches && + test_line_count = 1 fetches && + test_trace2_data promisor fetch_count 4 actual && + test_cmp ../expect actual && + + ! grep "child_start.*fetch.negotiationAlgorithm" trace2.output && + ! grep "\"key\":\"fetch_count\"" trace2.output + ) +' + test_done