From df56f6bdc2086ab3cd9684eba333099561276c19 Mon Sep 17 00:00:00 2001
From: Calle Wilund <calle@scylladb.com>
Date: Mon, 16 Mar 2026 20:13:32 +0100
Subject: [PATCH] memtable_test::memtable_flush_period: Change sleep to use
 injection signal instead

Fixes: SCYLLADB-942

Adds an injection signal _from_ table::seal_active_memtable to allow us to
reliably wait for flushing. And does so.

Closes scylladb/scylladb#29070

(cherry picked from commit 0013f22374bd659218477153e36bf91527070385)

Closes scylladb/scylladb#29116
---
 replica/table.cc            |  4 +++-
 test/boost/memtable_test.cc | 28 +++++++++++++++++++++++++---
 2 files changed, 28 insertions(+), 4 deletions(-)

diff --git a/replica/table.cc b/replica/table.cc
index 5cbf3781ea..25bbe4f42b 100644
--- a/replica/table.cc
+++ b/replica/table.cc
@@ -1766,7 +1766,9 @@ table::seal_active_memtable(compaction_group& cg, flush_permit&& flush_permit) n
         utils::get_local_injector().inject("table_seal_active_memtable_try_flush", []() {
             throw std::system_error(ENOSPC, std::system_category(), "Injected error");
         });
-        co_return co_await this->try_flush_memtable_to_sstable(cg, old, std::move(write_permit));
+        co_await this->try_flush_memtable_to_sstable(cg, old, std::move(write_permit));
+        // signal a memtable was sealed
+        utils::get_local_injector().receive_message("table_seal_post_flush_waiters");
     });
 
     undo_stats.reset();
diff --git a/test/boost/memtable_test.cc b/test/boost/memtable_test.cc
index 45f206b7ed..bb692de239 100644
--- a/test/boost/memtable_test.cc
+++ b/test/boost/memtable_test.cc
@@ -1004,7 +1004,20 @@ SEASTAR_TEST_CASE(memtable_flush_compresses_mutations) {
     }, db_config);
 }
 
-SEASTAR_TEST_CASE(memtable_flush_period) {
+static auto check_has_error_injection() {
+    return boost::unit_test::precondition([](auto){
+        return 
+#ifdef SCYLLA_ENABLE_ERROR_INJECTION
+            true
+#else
+            false
+#endif
+        ;
+    });
+}
+
+SEASTAR_TEST_CASE(memtable_flush_period, *check_has_error_injection()) {
+#ifdef SCYLLA_ENABLE_ERROR_INJECTION
     auto db_config = make_shared<db::config>();
     db_config->enable_cache.set(false);
     return do_with_cql_env_thread([](cql_test_env& env) {
@@ -1028,6 +1041,9 @@ SEASTAR_TEST_CASE(memtable_flush_period) {
         t.apply(m);
         BOOST_REQUIRE_EQUAL(t.sstables_count(), 0); // add mutation and check there are no sstables for this table
 
+        auto& errj = utils::get_local_injector();
+        errj.enable("table_seal_post_flush_waiters", true);
+
         // change schema to set memtable flush period
         // we use small value in this test but it is impossible to set the period less than 60000ms using ALTER TABLE construction
         schema_builder b(t.schema());
@@ -1035,8 +1051,10 @@ SEASTAR_TEST_CASE(memtable_flush_period) {
         schema_ptr s2 = b.build();
         t.set_schema(s2);
 
-        sleep(500ms).get(); // wait until memtable flush starts at least once
-        BOOST_REQUIRE(t.sstables_count() == 1 || t.get_stats().pending_flushes > 0);    // flush started
+        BOOST_TEST_MESSAGE("Wait for flush");
+        errj.inject("table_seal_post_flush_waiters", utils::wait_for_message(std::chrono::minutes(2))).get();
+        BOOST_TEST_MESSAGE("Flush received");
+
         BOOST_REQUIRE(eventually_true([&] { // wait until memtable will be flushed at least once
             return t.sstables_count() == 1;
         }));
@@ -1047,6 +1065,10 @@ SEASTAR_TEST_CASE(memtable_flush_period) {
             .produces(m)
             .produces_end_of_stream();
     }, db_config);
+#else
+    BOOST_TEST_MESSAGE("Skipping test as it depends on error injection. Please run in mode where it's enabled (debug,dev)");
+    return make_ready_future<>();
+#endif
 }
 
 SEASTAR_TEST_CASE(sstable_compaction_does_not_resurrect_data) {