Re: [PATCH v3 2/2] receive-pack: handle reference deletions separately

> On Fri, Jun 6, 2025 at 10:41 AM Karthik Nayak <karthik.188@gmail.com> wrote:
>>
>> In 9d2962a7c4 (receive-pack: use batched reference updates, 2025-05-19)
>> we updated the 'git-receive-pack(1)' command to use batched reference
>> updates. One edge case which was missed during this implementation was
>> when a user pushes multiple branches such as:
>>
>>   delete refs/heads/branch/conflict
>>   create refs/heads/branch
>>
>> Before using batched updates, the references would be applied
>> sequentially and hence no conflicts would arise. With batched updates,
>> while the first update applies, the second fails due to F/D conflict.
>
> Nit: it looks like "D/F conflict" is more often used than "F/D
> conflict" in the Git code base:
>
> $ git grep -i 'd/f conflict' | wc -l
> 119
> $ git grep -i 'f/d conflict' | wc -l
> 7
>
>> A
>> similar issue was present in 'git-fetch(1)' and was fixed by using
>> separating out reference pruning into a separate transaction. Apply a
>
> Maybe: s/using separating out/separating out/
>

>> similar mechanism for 'git-receive-pack(1)' and separate out reference
>> deletions into its own batch.
>>
>> This means 'git-receive-pack(1)' will now use upto two transactions,
>> whereas before using batched updates it would use _at least_ two
>> transactions. So using batched updates is still the better option.
>>
>> Add a test to validate this behavior.
>>
>> Signed-off-by: Karthik Nayak <karthik.188@gmail.com>
>> ---
>>  builtin/receive-pack.c | 100 ++++++++++++++++++++++++++++++++-----------------
>>  t/t5516-fetch-push.sh  |  17 +++++++--
>>  2 files changed, 79 insertions(+), 38 deletions(-)
>>
>> diff --git a/builtin/receive-pack.c b/builtin/receive-pack.c
>> index 9e3cfb85cf..8ee792d2f8 100644
>> --- a/builtin/receive-pack.c
>> +++ b/builtin/receive-pack.c
>> @@ -1867,47 +1867,79 @@ static void execute_commands_non_atomic(struct command *commands,
>>         const char *reported_error = NULL;
>>         struct strmap failed_refs = STRMAP_INIT;
>>
>> -       transaction = ref_store_transaction_begin(get_main_ref_store(the_repository),
>> -                                                 REF_TRANSACTION_ALLOW_FAILURE, &err);
>> -       if (!transaction) {
>> -               rp_error("%s", err.buf);
>> -               strbuf_reset(&err);
>> -               reported_error = "transaction failed to start";
>> -               goto failure;
>> -       }
>> +       /*
>> +        * Reference updates, where F/D conflicts shouldn't arise due to
>
> Nit: here also maybe "D/F conflicts" is more standard.
>

>> +        * one reference being deleted, while the other being created
>> +        * are treated as conflicts in batched updates. This is because
>> +        * we don't do conflict resolution inside a transaction. To
>> +        * mitigate this, delete references in a separate batch.
>> +        */
>> +       enum processing_phase {
>> +               PHASE_DELETIONS,
>> +               PHASE_OTHERS
>> +       };
>>
>> -       for (cmd = commands; cmd; cmd = cmd->next) {
>> -               if (!should_process_cmd(cmd) || cmd->run_proc_receive)
>> -                       continue;
>> +       for (enum processing_phase phase = PHASE_DELETIONS; phase <= PHASE_OTHERS; phase++) {
>> +               for (cmd = commands; cmd; cmd = cmd->next) {
>> +                       if (!should_process_cmd(cmd) || cmd->run_proc_receive)
>> +                               continue;
>>
>> -               cmd->error_string = update(cmd, si);
>> -       }
>> +                       if (phase == PHASE_DELETIONS && !is_null_oid(&cmd->new_oid))
>> +                               continue;
>> +                       else if (phase == PHASE_OTHERS && is_null_oid(&cmd->new_oid))
>> +                               continue;
>>
>> -       if (ref_transaction_commit(transaction, &err)) {
>> -               rp_error("%s", err.buf);
>> -               reported_error = "failed to update refs";
>> -               goto failure;
>> -       }
>> +                       /*
>> +                        * Lazily create a transaction only when we know there are
>> +                        * updates to be added.
>> +                        */
>> +                       if (!transaction) {
>> +                               transaction = ref_store_transaction_begin(get_main_ref_store(the_repository),
>> +                                                                         REF_TRANSACTION_ALLOW_FAILURE, &err);
>> +                               if (!transaction) {
>> +                                       rp_error("%s", err.buf);
>> +                                       strbuf_reset(&err);
>> +                                       reported_error = "transaction failed to s1tart";
>
> s/s1tart/start/
>

>> +                                       goto failure;
>> +                               }
>> +                       }
>>
>> -       ref_transaction_for_each_rejected_update(transaction,
>> -                                                ref_transaction_rejection_handler,
>> -                                                &failed_refs);
>> +                       cmd->error_string = update(cmd, si);
>> +               }
>>
>> -       if (strmap_empty(&failed_refs))
>> -               goto cleanup;
>> +               /*
>> +                * If no transaction was created, there is nothing to commit.
>> +                */
>
> Nit: the comment needs a single line, so maybe:
>
>               /* No transaction, so nothing to commit */
>

>> +               if (!transaction)
>> +                       goto cleanup;
>>
>> -failure:
>> -       for (cmd = commands; cmd; cmd = cmd->next) {
>> -               if (reported_error)
>> -                       cmd->error_string = reported_error;
>> -               else if (strmap_contains(&failed_refs, cmd->ref_name))
>> -                       cmd->error_string = strmap_get(&failed_refs, cmd->ref_name);
>> -       }
>> +               if (ref_transaction_commit(transaction, &err)) {
>> +                       rp_error("%s", err.buf);
>> +                       reported_error = "failed to update refs";
>> +                       goto failure;
>> +               }
>>
>> -cleanup:
>> -       ref_transaction_free(transaction);
>> -       strmap_clear(&failed_refs, 0);
>> -       strbuf_release(&err);
>> +               ref_transaction_for_each_rejected_update(transaction,
>> +                                                        ref_transaction_rejection_handler,
>> +                                                        &failed_refs);
>> +
>> +               if (strmap_empty(&failed_refs))
>> +                       goto cleanup;
>> +
>> +       failure:
>
> This label looks indented while previously it was right at the start
> of the line. Not sure if we have a standard for that, but a few quick
> greps seems to show that goto labels are most often at the start of
> the line.
>

>> +               for (cmd = commands; cmd; cmd = cmd->next) {
>> +                       if (reported_error)
>> +                               cmd->error_string = reported_error;
>> +                       else if (strmap_contains(&failed_refs, cmd->ref_name))
>> +                               cmd->error_string = strmap_get(&failed_refs, cmd->ref_name);
>> +               }
>> +
>> +       cleanup:
>
> Idem for how this label is indented.
>

>> +               ref_transaction_free(transaction);
>> +               transaction = NULL;
>> +               strmap_clear(&failed_refs, 0);
>> +               strbuf_release(&err);
>> +       }
>>  }