Materialized view drop the inner table (if any) drop the drop() method,
and this will lead to essure recursive drop() from the drop worker
thread, which will hang:
3 std::__1::condition_variable::wait<> ()
4 DB::DatabaseCatalog::waitTableFinallyDropped (this=0x7ffff7831500, uuid=...) at ../src/Interpreters/DatabaseCatalog.cpp:828
5 DB::InterpreterDropQuery::executeToTable (this=this@entry=0x7fff16ff88a0, table_id_=..., query=...) at ../src/Interpreters/InterpreterDropQuery.cpp:135
6 DB::InterpreterDropQuery::execute (this=this@entry=0x7fff16ff88a0) at ../contrib/libcxx/include/string:1474
7 DB::executeDropQuery (kind=kind@entry=DB::ASTDropQuery::Drop, global_context=..., target_table_id=...) at ../src/Storages/StorageMaterializedView.cpp:156
8 DB::StorageMaterializedView::drop (this=0x7ffefc348f40) at ../src/Storages/StorageMaterializedView.cpp:169
9 DB::DatabaseCatalog::dropTableFinally (this=this@entry=0x7ffff7831500, table=...) at ../src/Interpreters/DatabaseCatalog.cpp:775
10 DB::DatabaseCatalog::dropTableDataTask (this=0x7ffff7831500) at ../src/Interpreters/DatabaseCatalog.cpp:745
Fix this by dropping the inner table just before scheduling job the the
drop worker thread.
