purge_sys_t::wait_FTS sleeps 10ms, even if it does not have to wait.

The code reads like this

  bool paused;

  do

  {

    latch.wr_lock(SRW_LOCK_CALL);

    paused= m_FTS_paused || (also_sys && m_SYS_paused);

    latch.wr_unlock();

    std::this_thread::sleep_for(std::chrono::milliseconds(10));

  }

  while (paused);

it sleeps. without checking paused, even if paused is false.

It looks wrong, although perhaps it was intended for some purpose, e.g throttle purge activity.

Even if it was intended, then it still needs to be taken out of the function loop, and added to where the throttling needs to actually be, with appropritate comment.

Otherwise it adds 10 ms latency to all of its callers, and to the callers of its callers, which happens more than once during the purge

e.g in wait_FTS/clone_oldest_view/trx_purge and in wait_FTS/close_and_reopen/trx_attach_undo_recs/trx_purge code paths

Other thing : taking a write lock latch.wr_lock just to check the variable, and not change anything is this correct? Looks strange at least.