UPDATE gets access to history records because versioning conditions
are not set for VIEW. This leads to endless loop of inserting history
records when clustered index is rebuilt and ha_rnd_next() returns
newly inserted history record.
Return back original behavior of failing on write-locked table in
historical query.
35b679b9 assumed that SELECT_LEX::lock_type influences anything, but
actually at this point table is already locked. Original bug report
was tempesta-tech/mariadb#102
1. Removed TIMESTAMP/TRANSACTION unit auto-detection in favor of default TIMESTAMP.
Reasons:
1.1. rare practical use and doubtful advantage of such auto-detection;
1.2. it conflicts with MDEV-16226 (TRX_ID-based versioned tables performance improvement).
Needless check_unit membership removed.
2. SQL: versioning type handling refactoring
Vers_type_handler hierarchy stores versioning properties of type.
virtual Type_handler::vers() accesses specialization of
Vers_type_handler for specific type.
virtual Vers_type_handler::kind() returns versioning kind
(timestamp/trx_id).
Removed Type_handler::Vers_history_point_check_unit() in favor of
Type_handler::vers().
Renames:
require_timestamp() -> require_timestamp_error()
require_trx_id() -> require_trx_id_error()
EDIT by Alexander Barkov (@abarkov):
check_sys_fields() moved to Vers_type_handler::check_sys_fields()
