fix: fix kafka table engine

Author: wudidapaopao

src/Core/ServerSettings.cpp

@@ -796,7 +796,7 @@ The policy on how to perform a scheduling of CPU slots specified by `concurrent_
     DECLARE(UInt64, background_common_pool_size, 1, R"(The maximum number of threads that will be used for performing a variety of operations (mostly garbage collection) for [*MergeTree-engine](/engines/table-engines/mergetree-family) tables in the background.)", 0) \
     DECLARE(UInt64, background_buffer_flush_schedule_pool_size, 2, R"(The maximum number of threads that will be used for performing flush operations for [Buffer-engine tables](/engines/table-engines/special/buffer) in the background.)", 0) \
     DECLARE(UInt64, background_schedule_pool_size, 2, R"(The maximum number of threads that will be used for constantly executing some lightweight periodic operations for replicated tables, Kafka streaming, and DNS cache updates.)", 0) \
-    DECLARE(UInt64, background_message_broker_schedule_pool_size, 0, R"(The maximum number of threads that will be used for executing background operations for message streaming.)", 0) \
+    DECLARE(UInt64, background_message_broker_schedule_pool_size, 2, R"(The maximum number of threads that will be used for executing background operations for message streaming.)", 0) \
     DECLARE(UInt64, background_distributed_schedule_pool_size, 0, R"(The maximum number of threads that will be used for executing distributed sends.)", 0) \
     DECLARE(UInt64, tables_loader_foreground_pool_size, 0, R"(
     Sets the number of threads performing load jobs in foreground pool. The foreground pool is used for loading table synchronously before server start listening on a port and for loading tables that are waited for. Foreground pool has higher priority than background pool. It means that no job starts in background pool while there are jobs running in foreground pool.