From 166b293d06d33f1d3a3e954470ffb80ebe49591c Mon Sep 17 00:00:00 2001
From: Aleksandra Martyniuk <aleksandra.martyniuk@scylladb.com>
Date: Tue, 17 Mar 2026 17:21:46 +0100
Subject: [PATCH] test: add test_failed_tablet_rebuild_is_retried_on_alter

Test if alter keyspace statement with the current rf values will
fix the state of replicas.
---
 service/topology_coordinator.cc |  5 ++++
 test/cluster/test_tablets.py    | 43 +++++++++++++++++++++++++++++++++
 2 files changed, 48 insertions(+)

diff --git a/service/topology_coordinator.cc b/service/topology_coordinator.cc
index 74f4c7c282..233150b77a 100644
--- a/service/topology_coordinator.cc
+++ b/service/topology_coordinator.cc
@@ -3973,6 +3973,11 @@ future<std::optional<group0_guard>> topology_coordinator::maybe_start_tablet_res
 future<bool> topology_coordinator::maybe_retry_failed_rf_change_tablet_rebuilds(group0_guard guard) {
     rtlogger.debug("Retrying failed rebuilds");
 
+    if (utils::get_local_injector().enter("maybe_retry_failed_rf_change_tablet_rebuilds_skip")) {
+        rtlogger.debug("Skipping retrying failed rebuilds due to error injection");
+        co_return false;
+    }
+
     auto tmptr = get_token_metadata_ptr();
     utils::chunked_vector<canonical_mutation> updates;
     for (auto& ks_name : _db.get_tablets_keyspaces()) {
diff --git a/test/cluster/test_tablets.py b/test/cluster/test_tablets.py
index 355c9610a5..caf9db69bc 100644
--- a/test/cluster/test_tablets.py
+++ b/test/cluster/test_tablets.py
@@ -708,6 +708,49 @@ async def test_failed_tablet_rebuild_is_retried(request: pytest.FixtureRequest,
 
     await alter_keyspace("'dc1': ['rack1a', 'rack1b', 'rack1c']")
 
+@pytest.mark.asyncio
+@pytest.mark.skip_mode(mode='release', reason='error injections are not supported in release mode')
+async def test_failed_tablet_rebuild_is_retried_on_alter(manager: ManagerClient) -> None:
+    async def alter_keyspace(new_rf):
+        await cql.run_async(f"alter keyspace ks1 with replication = {{'class': 'NetworkTopologyStrategy', {new_rf}}};")
+
+    fail_injection = "rebuild_repair_stage_fail"
+    skip_fix_injection = "maybe_retry_failed_rf_change_tablet_rebuilds_skip"
+    config = {
+        "tablets_mode_for_new_keyspaces": "enabled",
+        "error_injections_at_startup": [skip_fix_injection, fail_injection],
+    }
+    cmdline = [
+        '--logger-log-level', 'load_balancer=debug',
+        '--smp=2',
+    ]
+
+    servers = [await manager.server_add(config=config, cmdline=cmdline, property_file={'dc': 'dc1', 'rack': 'rack1a'}),
+               await manager.server_add(config=config, cmdline=cmdline, property_file={'dc': 'dc1', 'rack': 'rack1b'}),
+               await manager.server_add(config=config, cmdline=cmdline, property_file={'dc': 'dc1', 'rack': 'rack1c'})]
+
+    cql = manager.get_cql()
+
+    await cql.run_async(f"create keyspace ks1 with replication = {{'class': 'NetworkTopologyStrategy', 'dc1': ['rack1a']}} and tablets = {{'initial': 4}};")
+    await cql.run_async("create table ks1.t (pk int primary key);")
+    await asyncio.gather(*[cql.run_async(f"INSERT INTO ks1.t (pk) VALUES ({pk});") for pk in range(16)])
+
+    await alter_keyspace("'dc1': ['rack1a', 'rack1b']")
+
+    tablet_replicas = await get_all_tablet_replicas(manager, servers[0], "ks1", "t")
+    assert len(tablet_replicas) == 4
+    for r in tablet_replicas:
+        assert len(r.replicas) == 1
+
+    [await manager.api.disable_injection(s.ip_addr, fail_injection) for s in servers]
+
+    await alter_keyspace("'dc1': ['rack1a', 'rack1b']")
+
+    tablet_replicas = await get_all_tablet_replicas(manager, servers[0], "ks1", "t")
+    assert len(tablet_replicas) == 4
+    for r in tablet_replicas:
+        assert len(r.replicas) == 2
+
 # Reproducer for https://github.com/scylladb/scylladb/issues/18110
 # Check that an existing cached read, will be cleaned up when the tablet it reads
 # from is migrated away.