To reduce contention between insert, erase and search, let us mimic
commit b08448de64 (MDEV-20612).
That is, btr_sea::partition::insert() and btr_sea::partition::erase()
will use a combination of a shared btr_sea::partition::latch and a
tiny page_hash_latch that is pushed down to the btr_sea::hash_table::array.
An exclusive btr_sea::partition::latch will be used in the final part of
btr_search_drop_page_hash_index(), where we must guarantee that all
entries will be removed, as well as in operations that affect an entire
adaptive hash index partition.
btr_sea::hash_chain: Chain of ahi_node hash buckets.
btr_sea::hash_table: A hash table that includes page_hash_latch
interleaved with hash_chain.
page_hash_latch::try_lock(): Attempt to acquire an exclusive latch
without waiting.
btr_search_guess_on_hash(): Acquire also the page_hash_latch in order
to prevent a concurrent modification of the hash bucket chain that our
lookup is traversing.
ha_insert_for_fold(): Remove. Invoke btr_sea::partition::insert() directly.
btr_sea::partition::erase(): Add template<bool ex> for indicating whether
an exclusive or a shared btr_sea::partition::latch is being held.
If the ex=false operation fails to free the memory,
btr_search_update_hash_on_delete() will retry with ex=true.
btr_sea::partition::cleanup_after_erase(): Add an overload for the case
where instead of holding an exclusive latch, we hold a shared latch
along with a page_hash_latch. When not holding an exclusve latch,
we may fail to free the memory, and the caller has to retry with an
exclusive latch.
btr_sea::partition::cleanup_after_erase_start(),
btr_sea::partition::cleanup_after_erase_finish(): Split from
cleanup_after_erase() to reduce the amount of code duplication.
btr_sea::partition::block_mutex: Protect only the linked list of blocks.
The spare block will exclusively be updated via Atomic_relaxed::exchange().
btr_sea::partition::rollback_insert(): Free the spare block in the unlikely
event that the adaptive hash index has been disabled after our invocation
of btr_sea::partition::prepare_insert().
ha_remove_all_nodes_to_page(): Merged to the only caller
btr_search_drop_page_hash_index().
ssux_lock_impl::wr_rd_downgrade(): Downgrade an X latch to S.
srw_lock_debug::wr_rd_downgrade(), srw_lock_impl::wr_rd_downgrade():
Downgrade from exclusive to shared. This operation is unavailable
if _WIN32 or SUX_LOCK_GENERIC is defined.
btr_search_build_page_hash_index(): Downgrade from exclusive to shared
part.latch before starting to insert records into the adaptive hash index.
In multi-batch operation, we preserve the last fr[] value in order to
ensure the correct operation when buf_block_t::LEFT_SIDE is not set.
9654b816f3