You can ignore this version. I realized I forgot to address some
feedback while I was sending mails out. I'll resend in some minutes.
Patrick
On Mon, Aug 09, 2021 at 10:00:39AM +0200, Patrick Steinhardt wrote:
> Hi,
>
> this is the fifth version of my series to speed up connectivity checks
> in the context of repos with many refs. While the original goal has been
> to speed up connectivity checks only, the series is now optimizing
> git-rev-list(1) in general to be able to more efficiently load
> references. Like this, `--not --all` is a lot faster in the context of
> many refs, but other usecases benefit, too.
>
> Changes compared to v4:
>
> - I've changed the interface to load commits via the commit-graph.
> Instead of the previous version where you'd had to pass in a
> `struct object`, which forced us to use `lookup_unknown_object()`,
> one now only passes in an object ID. If the object ID is found in
> the commit graph and if the corresponding object exists in the
> ODB, then we return the parsed commit object.
>
> This also avoids a previous pitfal: we'd have parsed the commit
> via the graph and thus had allocated the object even if the
> corresponding object didn't exist. While we knew to handle this in
> `get_reference()` by asserting object existence, any other caller
> which executes `lookup_commit()` would get the parsed commit and
> assume that it exists. This now cannot happen anymore given that
> we only create the commit object in case we know the ID exists in
> the ODB.
>
> - With this change, I could now drop the patch which avoided loading
> objects multiple times: we don't need `lookup_unknown_object()`
> anymore and thus don't thave the memory/perf tradeoff. And with
> the new interface to load commits via the graph, the deduplication
> only resulted in a ~1% speedup.
>
> Patrick
>
> Patrick Steinhardt (5):
> revision: separate walk and unsorted flags
> connected: do not sort input revisions
> revision: stop retrieving reference twice
> commit-graph: split out function to search commit position
> revision: avoid hitting packfiles when commits are in commit-graph
>
> Documentation/rev-list-options.txt | 8 ++-
> builtin/log.c | 2 +-
> builtin/revert.c | 3 +-
> commit-graph.c | 79 ++++++++++++++++++++----------
> commit-graph.h | 8 +++
> connected.c | 1 +
> revision.c | 42 +++++++++-------
> revision.h | 7 +--
> t/t6000-rev-list-misc.sh | 38 ++++++++++++++
> 9 files changed, 138 insertions(+), 50 deletions(-)
>
> Range-diff against v4:
> 1: 67232910ac = 1: 67232910ac revision: separate walk and unsorted flags
> 2: 9d7f484907 = 2: 9d7f484907 connected: do not sort input revisions
> 3: d8e63d0943 = 3: d8e63d0943 revision: stop retrieving reference twice
> 4: ba8df5cad0 < -: ---------- revision: avoid loading object headers multiple times
> 5: e33cd51ebf = 4: 549d85e5c2 commit-graph: split out function to search commit position
> 6: 900c5a9c60 ! 5: 4b893d943f revision: avoid hitting packfiles when commits are in commit-graph
> @@ Metadata
> ## Commit message ##
> revision: avoid hitting packfiles when commits are in commit-graph
>
> - When queueing references in git-rev-list(1), we try to either reuse an
> - already parsed object or alternatively we load the object header from
> - disk in order to determine its type. This is inefficient for commits
> - though in cases where we have a commit graph available: instead of
> - hitting the real object on disk to determine its type, we may instead
> - search the object graph for the object ID. In case it's found, we can
> - directly fill in the commit object, otherwise we can still hit the disk
> - to determine the object's type.
> + When queueing references in git-rev-list(1), we try to optimize parsing
> + of commits via the commit-graph. To do so, we first look up the object's
> + type, and if it is a commit we call `repo_parse_commit()` instead of
> + `parse_object()`. This is quite inefficient though given that we're
> + always uncompressing the object header in order to determine the type.
> + Instead, we can opportunistically search the commit-graph for the object
> + ID: in case it's found, we know it's a commit and can directly fill in
> + the commit object without having to uncompress the object header.
>
> - Expose a new function `parse_commit_in_graph_gently()`, which fills in
> - an object of unknown type in case we find its object ID in the graph.
> - This provides a big performance win in cases where there is a
> - commit-graph available in the repository in case we load lots of
> - references. The following has been executed in a real-world repository
> - with about 2.2 million refs:
> + Expose a new function `lookup_commit_in_graph()`, which tries to find a
> + commit in the commit-graph by ID, and convert `get_reference()` to use
> + this function. This provides a big performance win in cases where we
> + load references in a repository with lots of references pointing to
> + commits. The following has been executed in a real-world repository with
> + about 2.2 million refs:
>
> Benchmark #1: HEAD~: rev-list --unsorted-input --objects --quiet --not --all --not $newrev
> - Time (mean ± σ): 4.508 s ± 0.039 s [User: 4.131 s, System: 0.377 s]
> - Range (min … max): 4.455 s … 4.576 s 10 runs
> + Time (mean ± σ): 4.458 s ± 0.044 s [User: 4.115 s, System: 0.342 s]
> + Range (min … max): 4.409 s … 4.534 s 10 runs
>
> Benchmark #2: HEAD: rev-list --unsorted-input --objects --quiet --not --all --not $newrev
> - Time (mean ± σ): 3.072 s ± 0.031 s [User: 2.707 s, System: 0.365 s]
> - Range (min … max): 3.040 s … 3.144 s 10 runs
> + Time (mean ± σ): 3.089 s ± 0.015 s [User: 2.768 s, System: 0.321 s]
> + Range (min … max): 3.061 s … 3.105 s 10 runs
>
> Summary
> 'HEAD: rev-list --unsorted-input --objects --quiet --not --all --not $newrev' ran
> - 1.47 ± 0.02 times faster than 'HEAD~: rev-list --unsorted-input --objects --quiet --not --all --not $newrev'
> + 1.44 ± 0.02 times faster than 'HEAD~: rev-list --unsorted-input --objects --quiet --not --all --not $newrev'
>
> Signed-off-by: Patrick Steinhardt <ps@xxxxxx>
>
> @@ commit-graph.c: static int find_commit_pos_in_graph(struct commit *item, struct
> }
> }
>
> -+int parse_commit_in_graph_gently(struct repository *repo, struct object *object)
> ++struct commit *lookup_commit_in_graph(struct repository *repo, const struct object_id *id)
> +{
> + struct commit *commit;
> + uint32_t pos;
> +
> -+ if (object->parsed) {
> -+ if (object->type != OBJ_COMMIT)
> -+ return -1;
> -+ return 0;
> -+ }
> -+
> + if (!repo->objects->commit_graph)
> -+ return -1;
> ++ return NULL;
> ++ if (!search_commit_pos_in_graph(id, repo->objects->commit_graph, &pos))
> ++ return NULL;
> ++ if (!repo_has_object_file(repo, id))
> ++ return NULL;
> +
> -+ if (!search_commit_pos_in_graph(&object->oid, repo->objects->commit_graph, &pos))
> -+ return -1;
> -+
> -+ commit = object_as_type(object, OBJ_COMMIT, 1);
> ++ commit = lookup_commit(repo, id);
> + if (!commit)
> -+ return -1;
> -+ if (!fill_commit_in_graph(repo, commit, repo->objects->commit_graph, pos))
> -+ return -1;
> ++ return NULL;
> ++ if (commit->object.parsed)
> ++ return commit;
> +
> -+ return 0;
> ++ if (!fill_commit_in_graph(repo, commit, repo->objects->commit_graph, pos))
> ++ return NULL;
> ++
> ++ return commit;
> +}
> +
> static int parse_commit_in_graph_one(struct repository *r,
> @@ commit-graph.h: int open_commit_graph(const char *graph_file, int *fd, struct st
> int parse_commit_in_graph(struct repository *r, struct commit *item);
>
> +/*
> -+ * Given an object of unknown type, try to fill in the object in case it is a
> -+ * commit part of the commit-graph. Returns 0 if the object is a parsed commit
> -+ * or if it could be filled in via the commit graph, otherwise it returns -1.
> ++ * Look up the given commit ID in the commit-graph. This will only return a
> ++ * commit if the ID exists both in the graph and in the object database such
> ++ * that we don't return commits whose object has been pruned. Otherwise, this
> ++ * function returns `NULL`.
> + */
> -+int parse_commit_in_graph_gently(struct repository *repo, struct object *object);
> ++struct commit *lookup_commit_in_graph(struct repository *repo, const struct object_id *id);
> +
> /*
> * It is possible that we loaded commit contents from the commit buffer,
> @@ commit-graph.h: int open_commit_graph(const char *graph_file, int *fd, struct st
>
> ## revision.c ##
> @@ revision.c: static struct object *get_reference(struct rev_info *revs, const char *name,
> - struct object *object = lookup_unknown_object(revs->repo, oid);
> + unsigned int flags)
> + {
> + struct object *object;
> ++ struct commit *commit;
>
> - if (object->type == OBJ_NONE) {
> -- int type = oid_object_info(revs->repo, oid, NULL);
> -- if (type < 0 || !object_as_type(object, type, 1)) {
> -+ /*
> -+ * It's likely that the reference points to a commit, so we
> -+ * first try to look it up via the commit-graph. If successful,
> -+ * then we know it's a commit and don't have to unpack the
> -+ * object header. We still need to assert that the object
> -+ * exists, but given that we don't request any info about the
> -+ * object this is a lot faster than `oid_object_info()`.
> -+ */
> -+ if (parse_commit_in_graph_gently(revs->repo, object) < 0) {
> -+ int type = oid_object_info(revs->repo, oid, NULL);
> -+ if (type < 0 || !object_as_type(object, type, 1)) {
> -+ object = NULL;
> -+ goto out;
> -+ }
> -+ } else if (!repo_has_object_file(revs->repo, oid)) {
> - object = NULL;
> - goto out;
> - }
> + /*
> +- * If the repository has commit graphs, repo_parse_commit() avoids
> +- * reading the object buffer, so use it whenever possible.
> ++ * If the repository has commit graphs, we try to opportunistically
> ++ * look up the object ID in those graphs. Like this, we can avoid
> ++ * parsing commit data from disk.
> + */
> +- if (oid_object_info(revs->repo, oid, NULL) == OBJ_COMMIT) {
> +- struct commit *c = lookup_commit(revs->repo, oid);
> +- if (!repo_parse_commit(revs->repo, c))
> +- object = (struct object *) c;
> +- else
> +- object = NULL;
> +- } else {
> ++ commit = lookup_commit_in_graph(revs->repo, oid);
> ++ if (commit)
> ++ object = &commit->object;
> ++ else
> + object = parse_object(revs->repo, oid);
> +- }
> +
> + if (!object) {
> + if (revs->ignore_missing)
> --
> 2.32.0
>
Attachment:
signature.asc
Description: PGP signature
