On Fri, Jan 07, 2022 at 06:01:04PM -0800, Junio C Hamano wrote: > Patrick Steinhardt writes: > > > When deleting refs from the loose-files refs backend, then we need to be > > careful to also delete the same ref from the packed refs backend, if it > > exists. If we don't, then deleting the loose ref would "uncover" the > > packed ref. We thus always have to queue up deletions of refs for both > > the loose and the packed refs backend. This is done in two separate > > transactions, where the end result is that the reference-transaction > > hook is executed twice for the deleted refs. > > > > This behaviour is quite misleading: it's exposing implementation details > > of how the files backend works to the user, in contrast to the logical > > updates that we'd really want to expose via the hook. Worse yet, whether > > the hook gets executed once or twice depends on how well-packed the > > repository is: if the ref only exists as a loose ref, then we execute it > > once, otherwise if it is also packed then we execute it twice. > > If the ref only exists as a packed ref, what happens? ... > > > Fix this behaviour and don't execute the reference-transaction hook at > > all when refs in the packed-refs backend if it's driven by the files > > backend. > > ... We try to remove from the loose backend, which would say "nah, > it did not exist in my store". I am not sure if it should execute > the delete hook in such a case for the ref. But if it does not, not > running the hook in the ref transaction for packed backend driven by > the loose backend would mean nobody notifies the deletion of the > ref, no? This is shown in the test I've added, "deleting packed ref calls hook once". We create a new reference and pack it such that it doesn't exist as loose ref anymore, but only as a packed one. Updating that ref would've caused us to execute the hook twice before, once via the packed-backend and once via the loose-backend. With my fix we only execute it once via the loose-backend, even if it doesn't currently know it. This works because the loose-backend has to create a lock for the nonexistent reference such that no concurrent call touches the same ref. > To me, it seems that the only case this strategy would work > correctly is when the files backend calls deletion hook for a > request to delete nonexistent ref, which by itself sounds like a > problem. It does so only if the ref exists in either the loose or packed backend though. If trying to update a ref which exists in neither of those, then the reference transaction would fail with an "unable to resolve reference" error in `lock_raw_ref()`. So this should behave as expected: deleting a packed ref calls the hook once, deleting a nonexistent ref fails and doesn't call the hook at all. Patrick > > Signed-off-by: Patrick Steinhardt > > --- > > refs/files-backend.c | 9 ++++++--- > > t/t1416-ref-transaction-hooks.sh | 7 +------ > > 2 files changed, 7 insertions(+), 9 deletions(-) > > > > diff --git a/refs/files-backend.c b/refs/files-backend.c > > index 3c0f3027fe..9a20cb8fa8 100644 > > --- a/refs/files-backend.c > > +++ b/refs/files-backend.c > > @@ -1261,7 +1261,8 @@ static int files_delete_refs(struct ref_store *ref_store, const char *msg, > > if (packed_refs_lock(refs->packed_ref_store, 0, &err)) > > goto error; > > > > - transaction = ref_store_transaction_begin(refs->packed_ref_store, 0, &err); > > + transaction = ref_store_transaction_begin(refs->packed_ref_store, > > + REF_TRANSACTION_SKIP_HOOK, &err); > > if (!transaction) > > goto error; > > > > @@ -2775,7 +2776,8 @@ static int files_transaction_prepare(struct ref_store *ref_store, > > */ > > if (!packed_transaction) { > > packed_transaction = ref_store_transaction_begin( > > - refs->packed_ref_store, 0, err); > > + refs->packed_ref_store, > > + REF_TRANSACTION_SKIP_HOOK, err); > > if (!packed_transaction) { > > ret = TRANSACTION_GENERIC_ERROR; > > goto cleanup; > > @@ -3046,7 +3048,8 @@ static int files_initial_transaction_commit(struct ref_store *ref_store, > > &affected_refnames)) > > BUG("initial ref transaction called with existing refs"); > > > > - packed_transaction = ref_store_transaction_begin(refs->packed_ref_store, 0, err); > > + packed_transaction = ref_store_transaction_begin(refs->packed_ref_store, > > + REF_TRANSACTION_SKIP_HOOK, err); > > if (!packed_transaction) { > > ret = TRANSACTION_GENERIC_ERROR; > > goto cleanup; > > diff --git a/t/t1416-ref-transaction-hooks.sh b/t/t1416-ref-transaction-hooks.sh > > index f9d3d5213f..4e1e84a91f 100755 > > --- a/t/t1416-ref-transaction-hooks.sh > > +++ b/t/t1416-ref-transaction-hooks.sh > > @@ -175,16 +175,11 @@ test_expect_success 'deleting packed ref calls hook once' ' > > git update-ref -d refs/heads/to-be-deleted $POST_OID && > > > > # We only expect a single hook invocation, which is the logical > > - # deletion. But currently, we see two interleaving transactions, once > > - # for deleting the loose refs and once for deleting the packed ref. > > + # deletion. > > cat >expect <<-EOF && > > - prepared > > - $ZERO_OID $ZERO_OID refs/heads/to-be-deleted > > prepared > > $POST_OID $ZERO_OID refs/heads/to-be-deleted > > committed > > - $ZERO_OID $ZERO_OID refs/heads/to-be-deleted > > - committed > > $POST_OID $ZERO_OID refs/heads/to-be-deleted > > EOF