@matheusbsbs / matheus-bagliano / commits / 0e358de64a

fetch: use batched reference updates

The reference updates performed as a part of 'git-fetch(1)', take place one at a time. For each reference update, a new transaction is created and committed. This is necessary to ensure we can allow individual updates to fail without failing the entire command. The command also supports an '--atomic' mode, which uses a single transaction to update all of the references. But this mode has an all-or-nothing approach, where if a single update fails, all updates would fail. In 23fc8e4f61 (refs: implement batch reference update support, 2025-04-08), we introduced a new mechanism to batch reference updates. Under the hood, this uses a single transaction to perform a batch of reference updates, while allowing only individual updates to fail. Utilize this newly introduced batch update mechanism in 'git-fetch(1)'. This provides a significant bump in performance, especially when dealing with repositories with large number of references. Adding support for batched updates is simply modifying the flow to also create a batch update transaction in the non-atomic flow. With the reftable backend there is a 22x performance improvement, when performing 'git-fetch(1)' with 10000 refs: Benchmark 1: fetch: many refs (refformat = reftable, refcount = 10000, revision = master) Time (mean ± σ): 3.403 s ± 0.775 s [User: 1.875 s, System: 1.417 s] Range (min … max): 2.454 s … 4.529 s 10 runs Benchmark 2: fetch: many refs (refformat = reftable, refcount = 10000, revision = HEAD) Time (mean ± σ): 154.3 ms ± 17.6 ms [User: 102.5 ms, System: 56.1 ms] Range (min … max): 145.2 ms … 220.5 ms 18 runs Summary fetch: many refs (refformat = reftable, refcount = 10000, revision = HEAD) ran 22.06 ± 5.62 times faster than fetch: many refs (refformat = reftable, refcount = 10000, revision = master) In similar conditions, the files backend sees a 1.25x performance improvement: Benchmark 1: fetch: many refs (refformat = files, refcount = 10000, revision = master) Time (mean ± σ): 605.5 ms ± 9.4 ms [User: 117.8 ms, System: 483.3 ms] Range (min … max): 595.6 ms … 621.5 ms 10 runs Benchmark 2: fetch: many refs (refformat = files, refcount = 10000, revision = HEAD) Time (mean ± σ): 485.8 ms ± 4.3 ms [User: 91.1 ms, System: 396.7 ms] Range (min … max): 477.6 ms … 494.3 ms 10 runs Summary fetch: many refs (refformat = files, refcount = 10000, revision = HEAD) ran 1.25 ± 0.02 times faster than fetch: many refs (refformat = files, refcount = 10000, revision = master) With this we'll either be using a regular transaction or a batch update transaction. This helps cleanup some code which is no longer needed as we'll now always have some type of 'ref_transaction' object being propagated. One big change is that earlier, each individual update would propagate a failure. Whereas now, the `ref_transaction_for_each_rejected_update` function is called at the end of the flow to capture the exit status for 'git-fetch(1)' and also to print F/D conflict errors. This does change the order of the errors being printed, but the behavior stays the same. Since transaction errors are now explicitly defined as part of 76e760b999 (refs: introduce enum-based transaction error types, 2025-04-08), utilize them and get rid of custom errors defined within 'builtin/fetch.c'. Signed-off-by: Karthik Nayak <karthik.188@gmail.com> Signed-off-by: Junio C Hamano <gitster@pobox.com>

Karthik Nayak committed May 19, 2025 at 11:58 UTC 0e358de64a9e014575d11ef884bfc9beb931e37f

1 file changed +73 -54

builtin/fetch.c

+73 -54

@@ -640,9 +640,6 @@ static struct ref *get_ref_map(struct remote *remote,

640 return ref_map;

641 }

642

643 -#define STORE_REF_ERROR_OTHER 1

644 -#define STORE_REF_ERROR_DF_CONFLICT 2

645 -

643 static int s_update_ref(const char *action,

644 struct ref *ref,

645 struct ref_transaction *transaction,

@@ -650,7 +647,6 @@ static int s_update_ref(const char *action,

647 {

648 char *msg;

649 char *rla = getenv("GIT_REFLOG_ACTION");

653 - struct ref_transaction *our_transaction = NULL;

650 struct strbuf err = STRBUF_INIT;

651 int ret;

652

@@ -660,43 +656,10 @@ static int s_update_ref(const char *action,

656 rla = default_rla.buf;

657 msg = xstrfmt("%s: %s", rla, action);

658

663 - /*

664 - * If no transaction was passed to us, we manage the transaction

665 - * ourselves. Otherwise, we trust the caller to handle the transaction

666 - * lifecycle.

667 - */

668 - if (!transaction) {

669 - transaction = our_transaction = ref_store_transaction_begin(get_main_ref_store(the_repository),

670 - 0, &err);

671 - if (!transaction) {

672 - ret = STORE_REF_ERROR_OTHER;

673 - goto out;

674 - }

675 - }

676 -

659 ret = ref_transaction_update(transaction, ref->name, &ref->new_oid,

660 check_old ? &ref->old_oid : NULL,

661 NULL, NULL, 0, msg, &err);

680 - if (ret) {

681 - ret = STORE_REF_ERROR_OTHER;

682 - goto out;

683 - }

684 -

685 - if (our_transaction) {

686 - switch (ref_transaction_commit(our_transaction, &err)) {

687 - case 0:

688 - break;

689 - case REF_TRANSACTION_ERROR_NAME_CONFLICT:

690 - ret = STORE_REF_ERROR_DF_CONFLICT;

691 - goto out;

692 - default:

693 - ret = STORE_REF_ERROR_OTHER;

694 - goto out;

695 - }

696 - }

662

698 -out:

699 - ref_transaction_free(our_transaction);

663 if (ret)

664 error("%s", err.buf);

665 strbuf_release(&err);

@@ -1139,7 +1102,6 @@ N_("it took %.2f seconds to check forced updates; you can use\n"

1102 "to avoid this check\n");

1103

1104 static int store_updated_refs(struct display_state *display_state,

1142 - const char *remote_name,

1105 int connectivity_checked,

1106 struct ref_transaction *transaction, struct ref *ref_map,

1107 struct fetch_head *fetch_head,

@@ -1277,11 +1239,6 @@ static int store_updated_refs(struct display_state *display_state,

1239 }

1240 }

1241

1280 - if (rc & STORE_REF_ERROR_DF_CONFLICT)

1281 - error(_("some local refs could not be updated; try running\n"

1282 - " 'git remote prune %s' to remove any old, conflicting "

1283 - "branches"), remote_name);

1284 -

1242 if (advice_enabled(ADVICE_FETCH_SHOW_FORCED_UPDATES)) {

1243 if (!config->show_forced_updates) {

1244 warning(_(warn_show_forced_updates));

@@ -1365,9 +1322,8 @@ static int fetch_and_consume_refs(struct display_state *display_state,

1322 }

1323

1324 trace2_region_enter("fetch", "consume_refs", the_repository);

1368 - ret = store_updated_refs(display_state, transport->remote->name,

1369 - connectivity_checked, transaction, ref_map,

1370 - fetch_head, config);

1325 + ret = store_updated_refs(display_state, connectivity_checked,

1326 + transaction, ref_map, fetch_head, config);

1327 trace2_region_leave("fetch", "consume_refs", the_repository);

1328

1329 out:

@@ -1687,6 +1643,36 @@ cleanup:

1643 return result;

1644 }

1645

1646 +struct ref_rejection_data {

1647 + int *retcode;

1648 + int conflict_msg_shown;

1649 + const char *remote_name;

1650 +};

1651 +

1652 +static void ref_transaction_rejection_handler(const char *refname,

1653 + const struct object_id *old_oid UNUSED,

1654 + const struct object_id *new_oid UNUSED,

1655 + const char *old_target UNUSED,

1656 + const char *new_target UNUSED,

1657 + enum ref_transaction_error err,

1658 + void *cb_data)

1659 +{

1660 + struct ref_rejection_data *data = cb_data;

1661 +

1662 + if (err == REF_TRANSACTION_ERROR_NAME_CONFLICT && !data->conflict_msg_shown) {

1663 + error(_("some local refs could not be updated; try running\n"

1664 + " 'git remote prune %s' to remove any old, conflicting "

1665 + "branches"), data->remote_name);

1666 + data->conflict_msg_shown = 1;

1667 + } else {

1668 + const char *reason = ref_transaction_error_msg(err);

1669 +

1670 + error(_("fetching ref %s failed: %s"), refname, reason);

1671 + }

1672 +

1673 + *data->retcode = 1;

1674 +}

1675 +

1676 static int do_fetch(struct transport *transport,

1677 struct refspec *rs,

1678 const struct fetch_config *config)

@@ -1807,6 +1793,24 @@ static int do_fetch(struct transport *transport,

1793 retcode = 1;

1794 }

1795

1796 + /*

1797 + * If not atomic, we can still use batched updates, which would be much

1798 + * more performant. We don't initiate the transaction before pruning,

1799 + * since pruning must be an independent step, to avoid F/D conflicts.

1800 + *

1801 + * TODO: if reference transactions gain logical conflict resolution, we

1802 + * can delete and create refs (with F/D conflicts) in the same transaction

1803 + * and this can be moved above the 'prune_refs()' block.

1804 + */

1805 + if (!transaction) {

1806 + transaction = ref_store_transaction_begin(get_main_ref_store(the_repository),

1807 + REF_TRANSACTION_ALLOW_FAILURE, &err);

1808 + if (!transaction) {

1809 + retcode = -1;

1810 + goto cleanup;

1811 + }

1812 + }

1813 +

1814 if (fetch_and_consume_refs(&display_state, transport, transaction, ref_map,

1815 &fetch_head, config)) {

1816 retcode = 1;

@@ -1838,16 +1842,31 @@ static int do_fetch(struct transport *transport,

1842 free_refs(tags_ref_map);

1843 }

1844

1841 - if (transaction) {

1842 - if (retcode)

1843 - goto cleanup;

1845 + if (retcode)

1846 + goto cleanup;

1847

1845 - retcode = ref_transaction_commit(transaction, &err);

1848 + retcode = ref_transaction_commit(transaction, &err);

1849 + if (retcode) {

1850 + /*

1851 + * Explicitly handle transaction cleanup to avoid

1852 + * aborting an already closed transaction.

1853 + */

1854 + ref_transaction_free(transaction);

1855 + transaction = NULL;

1856 + goto cleanup;

1857 + }

1858 +

1859 + if (!atomic_fetch) {

1860 + struct ref_rejection_data data = {

1861 + .retcode = &retcode,

1862 + .conflict_msg_shown = 0,

1863 + .remote_name = transport->remote->name,

1864 + };

1865 +

1866 + ref_transaction_for_each_rejected_update(transaction,

1867 + ref_transaction_rejection_handler,

1868 + &data);

1869 if (retcode) {

1847 - /*

1848 - * Explicitly handle transaction cleanup to avoid

1849 - * aborting an already closed transaction.

1850 - */

1870 ref_transaction_free(transaction);

1871 transaction = NULL;

1872 goto cleanup;