[PATCH v4 05/16] refs/reftable: batch refname availability checks

[Patrick Steinhardt <ps@pks.im>]

Refactor the "reftable" backend to batch the availability check for
refnames. This does not yet have an effect on performance as we
essentially still call `refs_verify_refname_available()` in a loop, but
this will change in subsequent commits.

Signed-off-by: Patrick Steinhardt <ps@pks.im>
---
 refs/reftable-backend.c | 16 ++++++++++------
 1 file changed, 10 insertions(+), 6 deletions(-)

diff --git a/refs/reftable-backend.c b/refs/reftable-backend.c
index d39a14c5a46..2a90e7cb391 100644
--- a/refs/reftable-backend.c
+++ b/refs/reftable-backend.c
@@ -1069,6 +1069,7 @@ static int reftable_be_transaction_prepare(struct ref_store *ref_store,
 		reftable_be_downcast(ref_store, REF_STORE_WRITE|REF_STORE_MAIN, "ref_transaction_prepare");
 	struct strbuf referent = STRBUF_INIT, head_referent = STRBUF_INIT;
 	struct string_list affected_refnames = STRING_LIST_INIT_NODUP;
+	struct string_list refnames_to_check = STRING_LIST_INIT_NODUP;
 	struct reftable_transaction_data *tx_data = NULL;
 	struct reftable_backend *be;
 	struct object_id head_oid;
@@ -1224,12 +1225,7 @@ static int reftable_be_transaction_prepare(struct ref_store *ref_store,
 			 * can output a proper error message instead of failing
 			 * at a later point.
 			 */
-			ret = refs_verify_refname_available(ref_store, u->refname,
-							    &affected_refnames, NULL,
-							    transaction->flags & REF_TRANSACTION_FLAG_INITIAL,
-							    err);
-			if (ret < 0)
-				goto done;
+			string_list_append(&refnames_to_check, u->refname);
 
 			/*
 			 * There is no need to write the reference deletion
@@ -1379,6 +1375,13 @@ static int reftable_be_transaction_prepare(struct ref_store *ref_store,
 		}
 	}
 
+	string_list_sort(&refnames_to_check);
+	ret = refs_verify_refnames_available(ref_store, &refnames_to_check, &affected_refnames, NULL,
+					     transaction->flags & REF_TRANSACTION_FLAG_INITIAL,
+					     err);
+	if (ret < 0)
+		goto done;
+
 	transaction->backend_data = tx_data;
 	transaction->state = REF_TRANSACTION_PREPARED;
 
@@ -1394,6 +1397,7 @@ static int reftable_be_transaction_prepare(struct ref_store *ref_store,
 	string_list_clear(&affected_refnames, 0);
 	strbuf_release(&referent);
 	strbuf_release(&head_referent);
+	string_list_clear(&refnames_to_check, 0);
 
 	return ret;
 }

-- 
2.49.0.rc0.375.gae4b89d849.dirty