Description:
This patch is for merge VP engine to MariaDB.
Detail:
Send HA_EXTRA_ADD_CHILDREN_LIST,HA_EXTRA_ATTACH_CHILDREN,HA_EXTRA_IS_ATTACHED_CHILDREN,HA_EXTRA_DETACH_CHILDREN to partitioned handler threw table partitioning feature.
Add handler::set_top_table_and_fields() and handler::clear_top_table_fields() for pushdowning associating parent table and child table, parent table's columns and child table's columns.
Add ha_partition::get_child_handlers() for handling a part of partition.
Add HA_CAN_BG_SEARCH,HA_CAN_BG_INSERT,HA_CAN_BG_UPDATE to handler falgs for checking that child table are possible parallel searching, inserting, updating(deleting).
Add HA_CAN_MULTISTEP_MERGE to handler falgs and add HTON_CAN_MULTISTEP_MERGE to handlerton flags for checking handler and handlerton supports cascading merge.