Re: [PATCH v2 2/4] fetch: use batched reference updates
- From
Patrick Steinhardt <ps@pks.im>
- Date
- May 16, 2025, 05:40 UTC
- Message-ID
- <aCbP1SxncSVw2fCa@pks.im>
- In-Reply-To
- <20250515-501-update-git-fetch-1-to-use-partial-transactions-v2-2-80cbaaa55d2e@gmail.com>
On Thu, May 15, 2025 at 04:07:26PM +0200, Karthik Nayak wrote:
Show 23 quoted lines
> diff --git a/builtin/fetch.c b/builtin/fetch.c
> index 5279997c96..15eac2b1c2 100644
> --- a/builtin/fetch.c
> +++ b/builtin/fetch.c
> @@ -1688,6 +1644,37 @@ static int set_head(const struct ref *remote_refs, struct remote *remote)
> return result;
> }
>
> +struct ref_rejection_data {
> + int *retcode;
> + int conflict_msg_shown;
> + const char *remote_name;
> +};
> +
> +static void ref_transaction_rejection_handler(const char *refname,
> + const struct object_id *old_oid UNUSED,
> + const struct object_id *new_oid UNUSED,
> + const char *old_target UNUSED,
> + const char *new_target UNUSED,
> + enum ref_transaction_error err,
> + void *cb_data)
> +{
> + struct ref_rejection_data *data = (struct ref_rejection_data *)cb_data;Nit: unnecessary cast.
Show 14 quoted lines
> + if (err == REF_TRANSACTION_ERROR_NAME_CONFLICT && !data->conflict_msg_shown) {
> + error(_("some local refs could not be updated; try running\n"
> + " 'git remote prune %s' to remove any old, conflicting "
> + "branches"), data->remote_name);
> + data->conflict_msg_shown = 1;
> + } else {
> + char *reason = ref_transaction_error_msg(err);
> +
> + error(_("fetching ref %s failed: %s"), refname, reason);
> + free(reason);
> + }
> +
> + *data->retcode = 1;
> +}Okay, we stopped ignoring generic errors now and will print them. What I'm still unclear about: which exact errors do we accept now that `REF_TRANSACTION_ALLOW_FAILURE` is specified? Most of the error codes we probably want to accept, but what about `REF_TRANSACTION_ERROR_GENERIC`?
This makes me wonder a bit about the current layout of how we handle these errors. If the rejection handler was invoked while preparing the transaction for each reference as we go instead of afterwards we could decide on-the-fly whether a specific error should be ignored or not. That might lead to a design that is both more flexible and more obvious at the same time because error handling is now handled explicitly by the callsite that wants to ignore some errors.
Last but not least, I think that it would also allow us to decide ahead of time whether we want to commit. Right now we basically say "just commit it, whatever happens". But if I'm not mistaken, all the errors that we care about and that callers may want to ignore are already detected at prepare time. So if we already bubbled up relevant info while calling `ref_transaction_prepare()` the caller may then decide to not commit at all based on some criteria.
Sorry, I should've probably proposed this when you introducued this mechanism. But sometimes you only see things like that as we gain more users.
Show 12 quoted lines
> @@ -1808,6 +1795,24 @@ static int do_fetch(struct transport *transport, > retcode = 1; > } > > + /* > + * If not atomic, we can still use batched updates, which would be much > + * more performant. We don't initiate the transaction before pruning, > + * since pruning must be an independent step, to avoid F/D conflicts. > + * > + * TODO: if reference transactions gain logical conflict resolution, we > + * can delete and create refs (with F/D conflicts) in the same transaction > + * and this can be moved about the 'prune_refs()' block.
s/about/above/?
Patrick