Add explicit column aliases to SELECT statements in
slave_parallel_threads_basic to ensure consistent column names across
both normal and view-protocol modes.
The test sys_vars.slave_parallel_threads_basic.test was failing in
view-protocol mode due to different column naming behavior.
Without an explicit column alias, view-protocol mode generates an
automatic name (Name_exp_1) while normal mode uses the full expression
as the column name.
All new code of the whole pull request, including one or several files
that are either new files or modified ones, are contributed under the
BSD-new license. I am contributing on behalf of my employer Amazon Web
Services, Inc.
Delay spawning parallel replication worker threads until a slave SQL
thread is running, and de-spawn them when the last SQL thread stops.
This is especially useful to avoid needless threads on a master in a
setup where same my.cnf is used on masters and slaves.
