Antalya-26.3: Resolve currentDatabase() in Hybrid segment metadata

src/Storages/StorageDistributed.cpp

@@ -3008,6 +3008,13 @@ void registerStorageHybrid(StorageFactory & factory)
                 ColumnsDescription segment_columns = additional_table_function->getActualTableStructure(local_context, true);
                 replaceCurrentDatabaseFunction(normalized_table_function_ast, local_context);
 
+                // The clone above is only used for schema validation and in-memory segment
+                // execution. Resolve `currentDatabase()` in the original argument too, so the
+                // value written to the table metadata is a concrete database name. Otherwise
+                // startup ATTACH (which has no session database) resolves it to `default` and
+                // the segment fails to attach with UNKNOWN_TABLE.
+                replaceCurrentDatabaseFunction(engine_args[i], local_context);
+
                 validate_segment_schema(segment_columns, normalized_table_function_ast->formatForLogging());
 
                 // It's a table function - store the AST and cached schema for later execution

tests/integration/test_hybrid_table_restart/test.py

@@ -0,0 +1,74 @@
+import pytest
+
+from helpers.cluster import ClickHouseCluster
+
+cluster = ClickHouseCluster(__file__)
+node = cluster.add_instance("node", stay_alive=True)
+
+
+@pytest.fixture(scope="module")
+def start_cluster():
+    try:
+        cluster.start()
+        yield cluster
+    finally:
+        cluster.shutdown()
+
+
+def test_current_database_survives_restart(start_cluster):
+    """A Hybrid table created in a non-default database with currentDatabase() in a
+    segment must survive a server restart.
+
+    currentDatabase() has to be resolved to the actual database name and stored in
+    the table metadata at CREATE time. Otherwise the unresolved currentDatabase()
+    token is replayed during startup ATTACH, where there is no session database, so
+    it resolves to `default` and the segment points at the missing default.local_cold,
+    failing to attach with UNKNOWN_TABLE.
+    """
+    settings = {"allow_experimental_hybrid_table": 1}
+
+    node.query("CREATE DATABASE IF NOT EXISTS test_db")
+    node.query(
+        "CREATE TABLE test_db.local_hot (ts DateTime, value UInt64) ENGINE = MergeTree ORDER BY ts"
+    )
+    node.query(
+        "CREATE TABLE test_db.local_cold (ts DateTime, value UInt64) ENGINE = MergeTree ORDER BY ts"
+    )
+    node.query(
+        "INSERT INTO test_db.local_hot VALUES ('2025-10-15', 1), ('2025-11-01', 2)"
+    )
+    node.query(
+        "INSERT INTO test_db.local_cold VALUES ('2025-08-01', 3), ('2025-06-15', 4)"
+    )
+
+    # Run with test_db as the session database so currentDatabase() resolves to it.
+    node.query(
+        """
+        CREATE TABLE test_db.hybrid_t (ts DateTime, value UInt64)
+        ENGINE = Hybrid(
+            remote('localhost:9000', 'test_db', 'local_hot'),
+                ts > hybridParam('hybrid_watermark_hot', 'DateTime'),
+            remote('localhost:9000', currentDatabase(), 'local_cold'),
+                ts <= hybridParam('hybrid_watermark_hot', 'DateTime')
+        )
+        SETTINGS hybrid_watermark_hot = '2025-09-01'
+        """,
+        database="test_db",
+        settings=settings,
+    )
+
+    # Sanity: the table works before the restart, so any post-restart failure is
+    # attributable to metadata persistence, not to the table definition itself.
+    assert node.query("SELECT count() FROM test_db.hybrid_t", settings=settings).strip() == "4"
+
+    node.restart_clickhouse(kill=True)
+
+    # On the buggy build the stored metadata still contains currentDatabase(), which
+    # resolves to `default` during startup ATTACH, so this query fails with UNKNOWN_TABLE.
+    assert node.query("SELECT count() FROM test_db.hybrid_t", settings=settings).strip() == "4"
+
+    # The persisted definition must store the resolved database name, not the
+    # unresolved currentDatabase() token.
+    show = node.query("SHOW CREATE TABLE test_db.hybrid_t", settings=settings)
+    assert "currentDatabase()" not in show
+    assert "test_db" in show