Misc small InnoDB scalability fixes

commit 8389b45b7fa1a2ddab64050b0be3cdb3e1a937c1

Author: Sergey Vojtovich <svoj@mariadb.org>

Date:   Mon Jan 22 23:58:52 2018 +0400

    MDEV-15059 - Misc small InnoDB scalability fixes

    Moved mutex locking inside lock_rec_lock().

    Moved monitor increment out of mutex.

    Moved assertions that don't require protection out of mutex.

    Removed duplicate assertions.

    Moved duplicate debug injections into lock_rec_lock().

    Let monitor updates use relaxed memory order.

    Return directly without maintaining variables in lock_rec_lock_slow().

    Moved lock_rec_lock_fast() body into lock_rec_lock(): saves at least one

    trx_mutex_enter(), one switch() plus some code was moved out of mutex.

commit 04996939106bd35a2e8737de35a912ccc6b53ba4

Author: Sergey Vojtovich <svoj@mariadb.org>

Date:   Tue Jan 23 13:23:35 2018 +0400

    MDEV-15059 - Misc small InnoDB scalability fixes

    Moved lock_rec_lock_slow() inside lock_rec_lock().

commit 064bd78038ca8d76ca1612d849ccdcbbe4324110

Author: Sergey Vojtovich <svoj@mariadb.org>

Date:   Wed Jan 24 22:10:16 2018 +0400

    MDEV-15059 - Misc small InnoDB scalability fixes

    When cloning oldest view, don't copy ReadView::m_creator_trx_id.

    It means that the owner thread is now allowed to access this member

    without trx_sys.mutex protection.

    To achieve this we have to keep ReadView::m_creator_trx_id in

    ReadView::m_ids. This is required to not let purge thread process

    records owned by transaction associated with oldest view.

    It is only required if trsanction entered read-write mode before it's

    view was created.

    If transaction entered read-write mode after it's view was created

    (trx_set_rw_mode()), purge thread won't be allowed to touch it because

    m_low_limit_id >= m_creator_trx_id holds. Thus we don't have to add

    this transaction id to ReadView::m_ids.

    Cleanups:

    ReadView::ids_t: don't seem to make any sense, just complicate matters.

    ReadView::copy_trx_ids(): doesn't make sense anymore, integrated into

    caller.

    ReadView::copy_complete(): not needed anymore.

    ReadView copy constructores: don't seem to make any sense.

    trx_purge_truncate_history(): removed view argument, access

    purge_sys->view directly instead.

commit 55277e8840f359ed36a99359a7e21f03af72a78a

Author: Sergey Vojtovich <svoj@mariadb.org>

Date:   Thu Jan 25 18:29:59 2018 +0400

    MDEV-15059 - Misc small InnoDB scalability fixes

    Form better trx_sys API.