While waiting for for I/O completion, let us skip spin loops.
Even on fast storage, reading a page into the buffer pool takes
so long that a spin loop would only end up wasting CPU time.
block_lock::s_lock_nospin(): A no-spin variant of acquiring a shared
buffer page latch. Regular s_lock() always involveis a spin loop.
ssux_lock_impl::rd_lock_spin(), ssux_lock_impl::rd_lock_nospin():
Split from rd_wait().
ssux_lock_impl::rd_lock(): Invoke either rd_lock_nospin() or
rd_lock_try() and rd_lock_spin().
buf_page_get_low(): After acquiring a page latch on an io-fixed block,
try to optimize operations on the page latch.
67da6e6388