Let me re-share some questions/suggestions/objections I got on a patch I shared with similar changes: https://lore.kernel.org/git/pull.1228.git.1651676435634.gitgitgadget@xxxxxxxxx/ There's a lot to like about the change; it fixes the incorrect invocation of the reference-transaction hooks when (bulk) deleting refs, but there is a down-side that Patrick pointed out. We never got to a satisfactory solution, so let me reshare his feedback to pick up the discussion. Patrick: > I really like these changes given that they simplify things, but I > wonder whether we can do them. In the preimage we're eagerly removing > loose refs: any error encountered when deleting a reference is recorded, > but we keep on trying to remove the other refs, as well. With the new > behaviour we now create a single transaction for all refs and try to > commit it. This also means that we'll abort the transaction when locking > any of the refs fails, which is a change in behaviour. > > The current behaviour is explicitly documented in `refs.h:refs_delete_refs()`: > > /* > * Delete the specified references. If there are any problems, emit > * errors but attempt to keep going (i.e., the deletes are not done in > * an all-or-nothing transaction). msg and flags are passed through to > * ref_transaction_delete(). > */ > int refs_delete_refs(struct ref_store *refs, const char *msg, > struct string_list *refnames, unsigned int flags); > > There are multiple callsites of this function via `delete_refs()`. Now > honestly, most of these callsites look somewhat broken: > > - `bisect.c` simply does its best to clean up bisect state. This > usecase looks fine to me. > > - `builtin/branch.c` reports the branches as deleted even if > `delete_refs()` failed. > > - `builtin/remote.c` also misreports the deleted branches for the > `prune` verb. The `rm` verb looks alright: if deletion of any > branch failed then it doesn't prune the remote's config in the end > and reports an error. > > - `builtin/fetch.c` also misreports deleted branches with `--prune`. > > So most of these commands incorrectly handle the case where only a > subset of branches has been deleted. This raises the question whether > the interface provided by `refs_delete_refs()` is actually sensible if > it's so easy to get wrong. It doesn't even report which branches could > be removed and which couldn't. Furthermore, the question is whether new > backends like the reftable backend which write all refs into a single > slice would actually even be in a position to efficiently retain > semantics of this function. > > I'm torn. There are valid usecases for eagerly deleting refs even if a > subset of deletions failed, making this change a tough sell, but most of > the callsites don't actually handle this correctly in the first place. At the time, the only solution I could see was to switch to transaction-per-ref semantics, but this results in bad performance when deleting tens of thousands of refs. One option might be to optimistically try to delete the refs in a single transaction. If that fails for whatever reason and multiple ref deletions are requested, we could fall back to a transaction-per-ref approach. That'd keep the common case fast, and still provide best effort deletes. Thoughts? Cheers, Michael Heemskerk On Fri, Jul 29, 2022 at 12:13 PM Jiang Xin <worldhello.net@xxxxxxxxx> wrote: > > From: Jiang Xin <zhiyou.jx@xxxxxxxxxxxxxxx> > > When delete references using "git branch -d" or "git tag -d", there will > be duplicate call of "reference-transaction committed" for same refs. > This is because "refs_delete_refs()" is called twice, once for > files-backend and once for packed-backend, and we used to reinvented the > wheel in "files_delete_refs()" and "packed_delete_refs()". By removing > "packed_delete_refs()" and reimplement "files_delete_refs()", the > "reference-transaction" hook will run only once for deleted branches and > tags. > > The behavior of the following git commands and the last two testcases > have been fixed in t1416: > > * git branch -d <branch> > * git tag -d <tag> > > A testcase in t5510 is broken because we used to call the function > "packed_refs_lock()", but it is not necessary if the deleted reference > is not in the "packed-refs" file. > > Signed-off-by: Jiang Xin <zhiyou.jx@xxxxxxxxxxxxxxx> > --- > refs/files-backend.c | 21 ++++++------- > refs/packed-backend.c | 51 +------------------------------- > t/t1416-ref-transaction-hooks.sh | 4 +-- > t/t5510-fetch.sh | 17 +++++++++++ > 4 files changed, 29 insertions(+), 64 deletions(-) > > diff --git a/refs/files-backend.c b/refs/files-backend.c > index 8baea66e58..21426efaae 100644 > --- a/refs/files-backend.c > +++ b/refs/files-backend.c > @@ -1268,31 +1268,27 @@ static int files_pack_refs(struct ref_store *ref_store, unsigned int flags) > static int files_delete_refs(struct ref_store *ref_store, const char *msg, > struct string_list *refnames, unsigned int flags) > { > - struct files_ref_store *refs = > - files_downcast(ref_store, REF_STORE_WRITE, "delete_refs"); > + struct ref_transaction *transaction; > struct strbuf err = STRBUF_INIT; > int i, result = 0; > > if (!refnames->nr) > return 0; > > - if (packed_refs_lock(refs->packed_ref_store, 0, &err)) > - goto error; > - > - if (refs_delete_refs(refs->packed_ref_store, msg, refnames, flags)) { > - packed_refs_unlock(refs->packed_ref_store); > + transaction = ref_store_transaction_begin(ref_store, &err); > + if (!transaction) > goto error; > - } > - > - packed_refs_unlock(refs->packed_ref_store); > > for (i = 0; i < refnames->nr; i++) { > const char *refname = refnames->items[i].string; > - > - if (refs_delete_ref(&refs->base, msg, refname, NULL, flags)) > + if (ref_transaction_delete(transaction, refname, NULL, > + flags, msg, &err)) > result |= error(_("could not remove reference %s"), refname); > } > + if (ref_transaction_commit(transaction, &err)) > + goto error; > > + ref_transaction_free(transaction); > strbuf_release(&err); > return result; > > @@ -1309,6 +1305,7 @@ static int files_delete_refs(struct ref_store *ref_store, const char *msg, > else > error(_("could not delete references: %s"), err.buf); > > + ref_transaction_free(transaction); > strbuf_release(&err); > return -1; > } > diff --git a/refs/packed-backend.c b/refs/packed-backend.c > index 97b6837767..fdb7a0a52c 100644 > --- a/refs/packed-backend.c > +++ b/refs/packed-backend.c > @@ -1519,55 +1519,6 @@ static int packed_initial_transaction_commit(struct ref_store *ref_store, > return ref_transaction_commit(transaction, err); > } > > -static int packed_delete_refs(struct ref_store *ref_store, const char *msg, > - struct string_list *refnames, unsigned int flags) > -{ > - struct packed_ref_store *refs = > - packed_downcast(ref_store, REF_STORE_WRITE, "delete_refs"); > - struct strbuf err = STRBUF_INIT; > - struct ref_transaction *transaction; > - struct string_list_item *item; > - int ret; > - > - (void)refs; /* We need the check above, but don't use the variable */ > - > - if (!refnames->nr) > - return 0; > - > - /* > - * Since we don't check the references' old_oids, the > - * individual updates can't fail, so we can pack all of the > - * updates into a single transaction. > - */ > - > - transaction = ref_store_transaction_begin(ref_store, &err); > - if (!transaction) > - return -1; > - > - for_each_string_list_item(item, refnames) { > - if (ref_transaction_delete(transaction, item->string, NULL, > - flags, msg, &err)) { > - warning(_("could not delete reference %s: %s"), > - item->string, err.buf); > - strbuf_reset(&err); > - } > - } > - > - ret = ref_transaction_commit(transaction, &err); > - > - if (ret) { > - if (refnames->nr == 1) > - error(_("could not delete reference %s: %s"), > - refnames->items[0].string, err.buf); > - else > - error(_("could not delete references: %s"), err.buf); > - } > - > - ref_transaction_free(transaction); > - strbuf_release(&err); > - return ret; > -} > - > static int packed_pack_refs(struct ref_store *ref_store, unsigned int flags) > { > /* > @@ -1595,7 +1546,7 @@ struct ref_storage_be refs_be_packed = { > > .pack_refs = packed_pack_refs, > .create_symref = NULL, > - .delete_refs = packed_delete_refs, > + .delete_refs = NULL, > .rename_ref = NULL, > .copy_ref = NULL, > > diff --git a/t/t1416-ref-transaction-hooks.sh b/t/t1416-ref-transaction-hooks.sh > index df75e5727c..f64166f9d7 100755 > --- a/t/t1416-ref-transaction-hooks.sh > +++ b/t/t1416-ref-transaction-hooks.sh > @@ -744,7 +744,7 @@ test_expect_success "branch: rename branches" ' > test_cmp_heads_and_tags -C workdir expect > ' > > -test_expect_failure "branch: remove branches" ' > +test_expect_success "branch: remove branches" ' > test_when_finished "rm -f $HOOK_OUTPUT" && > > cat >expect <<-EOF && > @@ -873,7 +873,7 @@ test_expect_success "tag: update refs to create loose refs" ' > test_cmp_heads_and_tags -C workdir expect > ' > > -test_expect_failure "tag: remove tags with mixed ref_stores" ' > +test_expect_success "tag: remove tags with mixed ref_stores" ' > test_when_finished "rm -f $HOOK_OUTPUT" && > > cat >expect <<-EOF && > diff --git a/t/t5510-fetch.sh b/t/t5510-fetch.sh > index b45879a760..22de7ac9ec 100755 > --- a/t/t5510-fetch.sh > +++ b/t/t5510-fetch.sh > @@ -168,6 +168,8 @@ test_expect_success REFFILES 'fetch --prune fails to delete branches' ' > cd "$D" && > git clone . prune-fail && > cd prune-fail && > + git update-ref refs/remotes/origin/extrabranch main~ && > + git pack-refs --all && > git update-ref refs/remotes/origin/extrabranch main && > : this will prevent --prune from locking packed-refs for deleting refs, but adding loose refs still succeeds && > >.git/packed-refs.new && > @@ -175,6 +177,21 @@ test_expect_success REFFILES 'fetch --prune fails to delete branches' ' > test_must_fail git fetch --prune origin > ' > > +test_expect_success REFFILES 'fetch --prune ok for loose refs not in locked packed-refs' ' > + test_when_finished "cd \"$D\"; rm -rf \"prune-ok-ref-not-packed\"" && > + cd "$D" && > + git clone . prune-ok-ref-not-packed && > + ( > + cd prune-ok-ref-not-packed && > + git update-ref refs/remotes/origin/extrabranch main && > + : for loose refs not in packed-refs, we can delete them even the packed-refs is locked && > + :>.git/packed-refs.new && > + > + git fetch --prune origin && > + test_must_fail git rev-parse refs/remotes/origin/extrabranch -- > + ) > +' > + > test_expect_success 'fetch --atomic works with a single branch' ' > test_when_finished "rm -rf \"$D\"/atomic" && > > -- > 2.36.1.25.gc87d5ad63a.dirty >
