Polling for srv_purge_should_exit() once every millisecond is enough.

- commit ea37b144 (MDEV-16678) caused
a regression. when purge thread tries to open the table for virtual
column computation, there is no need to acquire MDL for the table.
Because purge thread already hold MDL for the table

It looks buffer over flow of spider_unique_id_buf. It requires to analyze on reproducing environment, but I extend this first.

Fix issue caused by using spider_bgs_mode = 2 when Spider use limit_mode = 1 internally for data nodes.

Conflicts:
	storage/spider/spd_conn.cc

Add looping check

Conflicts:
	sql/table.h

Change the following function for batch call instead of each partition
- store_lock
- external_lock
- start_stmt
- extra
- cond_push
- info_push
- top_table

Add `append_system_key_parts` call inside `fast_alter_partition_table` during new partition creation.

cmp_max is used instead of cmp to compare key_parts

Insert worked incorrect as well. RocksDB used table->record[0] internally to store some
intermediate results for key conversion, during index searching among other operations.
So table->record[0] is spoiled during ha_rnd_index_map in ha_check_overlaps, so in turn
the broken record data was inserted.

The fix is to store RocksDB intermediate result in its own buffer instead of table->record[0].

`rocksdb` MTR suite is is checked and runs fine.
No need for additional tests. The existing overlaps.test covers the case completely.
However, I am not going to add anything related to rocksdb to suite, to keep it away
from additional dependencies.

To run tests with RocksDB engine, one can add following to engines.combinations:
[rocksdb]
plugin-load=$HA_ROCKSDB_SO
default-storage-engine=rocksdb
rocksdb

User-visible changes: The INFORMATION_SCHEMA views INNODB_BUFFER_PAGE
and INNODB_BUFFER_PAGE_LRU will report a dummy value FLUSH_TYPE=0
and will no longer report the PAGE_STATE value READY_FOR_USE.

We will remove some fields from buf_page_t and move much code to
member functions of buf_pool_t and buf_page_t, so that the access
rules of data members can be enforced consistently.

Evicting or adding pages in buf_pool.LRU will remain covered by
buf_pool.mutex.

Evicting or adding pages in buf_pool.page_hash will remain
covered by both buf_pool.mutex and the buf_pool.page_hash X-latch.

After this fix, buf_pool.page_hash lookups can entirely
avoid acquiring buf_pool.mutex, only relying on
buf_pool.hash_lock_get() S-latch.

Similarly, buf_flush_check_neighbors() can will rely solely on
buf_pool.mutex, no buf_pool.page_hash latch at all.

The buf_pool.mutex is rather contended in I/O heavy benchmarks,
especially when the workload does not fit in the buffer pool.

The first attempt to alleviate the contention was the
buf_pool_t::mutex split in
commit 4ed7082e
which introduced buf_block_t::mutex, which we are now removing.

Later, multiple instances of buf_pool_t were introduced
in commit c18084f7
and recently removed by us in
commit 1a6f708e (MDEV-15058).

UNIV_BUF_DEBUG: Remove. This option to enable some buffer pool
related debugging in otherwise non-debug builds has not been used
for years. Instead, we have been using UNIV_DEBUG, which is enabled
in CMAKE_BUILD_TYPE=Debug.

buf_block_t::mutex, buf_pool_t::zip_mutex: Remove. We can mainly rely on
std::atomic and the buf_pool.page_hash latches, and in some cases
depend on buf_pool.mutex or buf_pool.flush_list_mutex just like before.
We must always release buf_block_t::lock before invoking
unfix() or io_unfix(), to prevent a glitch where a block that was
added to the buf_pool.free list would apper X-latched. See
commit c5883deb how this glitch
was finally caught in a debug environment.

We move some buf_pool_t::page_hash specific code from the
ha and hash modules to buf_pool, for improved readability.

buf_pool_t::close(): Assert that all blocks are clean, except
on aborted startup or crash-like shutdown.

buf_pool_t::validate(): No longer attempt to validate
n_flush[] against the number of BUF_IO_WRITE fixed blocks,
because buf_page_t::flush_type no longer exists.

buf_pool_t::watch_set(): Replaces buf_pool_watch_set().
Reduce mutex contention by separating the buf_pool.watch[]
allocation and the insert into buf_pool.page_hash.

buf_pool_t::page_hash_lock<bool exclusive>(): Acquire a
buf_pool.page_hash latch.
Replaces and extends buf_page_hash_lock_s_confirm()
and buf_page_hash_lock_x_confirm().

buf_pool_t::READ_AHEAD_PAGES: Renamed from BUF_READ_AHEAD_PAGES.

buf_pool_t::curr_size, old_size, read_ahead_area, n_pend_reads:
Use Atomic_counter.

buf_pool_t::running_out(): Replaces buf_LRU_buf_pool_running_out().

buf_pool_t::LRU_remove(): Remove a block from the LRU list
and return its predecessor. Incorporates buf_LRU_adjust_hp(),
which was removed.

buf_page_get_gen(): Remove a redundant call of fsp_is_system_temporary(),
for mode == BUF_GET_IF_IN_POOL_OR_WATCH, which is only used by
BTR_DELETE_OP (purge), which is never invoked on temporary tables.

buf_free_from_unzip_LRU_list_batch(): Avoid redundant assignments.

buf_LRU_free_from_unzip_LRU_list(): Simplify the loop condition.

buf_LRU_free_page(): Clarify the function comment.

buf_flush_check_neighbor(), buf_flush_check_neighbors():
Rewrite the construction of the page hash range. We will hold
the buf_pool.mutex for up to buf_pool.read_ahead_area (at most 64)
consecutive lookups of buf_pool.page_hash.

buf_flush_page_and_try_neighbors(): Remove.
Merge to its only callers, and remove redundant operations in
buf_flush_LRU_list_batch().

buf_read_ahead_random(), buf_read_ahead_linear(): Rewrite.
Do not acquire buf_pool.mutex, and iterate directly with page_id_t.

ut_2_power_up(): Remove. my_round_up_to_next_power() is inlined
and avoids any loops.

fil_page_get_prev(), fil_page_get_next(), fil_addr_is_null(): Remove.

buf_flush_page(): Add a fil_space_t* parameter. Minimize the
buf_pool.mutex hold time. buf_pool.n_flush[] is no longer updated
atomically with the io_fix, and we will protect most buf_block_t
fields with buf_block_t::lock. The function
buf_flush_write_block_low() is removed and merged here.

buf_page_init_for_read(): Use static linkage. Initialize the newly
allocated block and acquire the exclusive buf_block_t::lock while not
holding any mutex.

IORequest::IORequest(): Remove the body. We only need to invoke
set_punch_hole() in buf_flush_page() and nowhere else.

buf_page_t::flush_type: Remove. Replaced by IORequest::flush_type.
This field is only used during a fil_io() call.
That function already takes IORequest as a parameter, so we had
better introduce  for the rarely changing field.

buf_block_t::init(): Replaces buf_page_init().

buf_page_t::init(): Replaces buf_page_init_low().

buf_block_t::initialise(): Initialise many fields, but
keep the buf_page_t::state(). Both buf_pool_t::validate() and
buf_page_optimistic_get() requires that buf_page_t::in_file()
be protected atomically with buf_page_t::in_page_hash
and buf_page_t::in_LRU_list.

buf_page_optimistic_get(): Now that buf_block_t::mutex
no longer exists, we must check buf_page_t::io_fix()
after acquiring the buf_pool.page_hash lock, to detect
whether buf_page_init_for_read() has been initiated.
We will also check the io_fix() before acquiring hash_lock
in order to avoid unnecessary computation.
The field buf_block_t::modify_clock (protected by buf_block_t::lock)
allows buf_page_optimistic_get() to validate the block.

buf_page_t::real_size: Remove. It was only used while flushing
pages of page_compressed tables.

buf_page_encrypt(): Add an output parameter that allows us ot eliminate
buf_page_t::real_size. Replace a condition with debug assertion.

buf_page_should_punch_hole(): Remove.

buf_dblwr_t::add_to_batch(): Replaces buf_dblwr_add_to_batch().
Add the parameter size (to replace buf_page_t::real_size).

buf_dblwr_t::write_single_page(): Replaces buf_dblwr_write_single_page().
Add the parameter size (to replace buf_page_t::real_size).

fil_system_t::detach(): Replaces fil_space_detach().
Ensure that fil_validate() will not be violated even if
fil_system.mutex is released and reacquired.

fil_node_t::complete_io(): Renamed from fil_node_complete_io().

fil_node_t::close_to_free(): Replaces fil_node_close_to_free().
Avoid invoking fil_node_t::close() because fil_system.n_open
has already been decremented in fil_space_t::detach().

BUF_BLOCK_READY_FOR_USE: Remove. Directly use BUF_BLOCK_MEMORY.

BUF_BLOCK_ZIP_DIRTY: Remove. Directly use BUF_BLOCK_ZIP_PAGE,
and distinguish dirty pages by buf_page_t::oldest_modification().

BUF_BLOCK_POOL_WATCH: Remove. Use BUF_BLOCK_NOT_USED instead.
This state was only being used for buf_page_t that are in
buf_pool.watch.

buf_pool_t::watch[]: Remove pointer indirection.

buf_page_t::in_flush_list: Remove. It was set if and only if
buf_page_t::oldest_modification() is nonzero.

buf_page_decrypt_after_read(), buf_corrupt_page_release(),
buf_page_check_corrupt(): Change the const fil_space_t* parameter
to const fil_node_t& so that we can report the correct file name.

buf_page_monitor(): Declare as an ATTRIBUTE_COLD global function.

buf_page_io_complete(): Split to buf_page_read_complete() and
buf_page_write_complete().

buf_dblwr_t::in_use: Remove.

buf_dblwr_t::buf_block_array: Add IORequest::flush_t.

buf_dblwr_sync_datafiles(): Remove. It was a useless wrapper of
os_aio_wait_until_no_pending_writes().

buf_flush_write_complete(): Declare static, not global.
Add the parameter IORequest::flush_t.

buf_flush_freed_page(): Simplify the code.

recv_sys_t::flush_lru: Renamed from flush_type and changed to bool.

fil_read(), fil_write(): Replaced with direct use of fil_io().

fil_buffering_disabled(): Remove. Check srv_file_flush_method directly.

fil_mutex_enter_and_prepare_for_io(): Return the resolved
fil_space_t* to avoid a duplicated lookup in the caller.

fil_report_invalid_page_access(): Clean up the parameters.

fil_io(): Return fil_io_t, which comprises fil_node_t and error code.
Always invoke fil_space_t::acquire_for_io() and let either the
sync=true caller or fil_aio_callback() invoke
fil_space_t::release_for_io().

fil_aio_callback(): Rewrite to replace buf_page_io_complete().

fil_check_pending_operations(): Remove a parameter, and remove some
redundant lookups.

fil_node_close_to_free(): Wait for n_pending==0. Because we no longer
do an extra lookup of the tablespace between fil_io() and the
completion of the operation, we must give fil_node_t::complete_io() a
chance to decrement the counter.

fil_close_tablespace(): Remove unused parameter trx, and document
that this is only invoked during the error handling of IMPORT TABLESPACE.

row_import_discard_changes(): Merged with the only caller,
row_import_cleanup(). Do not lock up the data dictionary while
invoking fil_close_tablespace().

logs_empty_and_mark_files_at_shutdown(): Do not invoke
fil_close_all_files(), to avoid a !needs_flush assertion failure
on fil_node_t::close().

innodb_shutdown(): Invoke os_aio_free() before fil_close_all_files().

fil_close_all_files(): Invoke fil_flush_file_spaces()
to ensure proper durability.

thread_pool::unbind(): Fix a crash that would occur on Windows
after srv_thread_pool->disable_aio() and os_file_close().
This fix was submitted by Vladislav Vaintroub.

Thanks to Matthias Leich and Axel Schwenke for extensive testing,
Vladislav Vaintroub for helpful comments, and Eugene Kosov for a review.

HAVE_AIOWAIT had not been disabled and unused for at least 10 years.

* FreeBSD calls amd64 what Linux calls x86_64
* signal returns void (*)(int)
* struct pam_message has char*, not const char*
* krb5_free_unparsed_name exists, but is deprecated

ORDER BY fixed for JSON_ARRAYAGG.

Item_func_groupconcat::print() should be fixed to work for the derived
classes.

We have to include NULL in the result which the GOUP_CONCAT doesn't
always do. Also converting should be done into another String instance
as these can be same.

Ensure that FTS_MSG_STOP is the very last message, and nothing comes after
it in fts_optimize_shutdown.

Stop the timer to ensure that.

Use symbolic constant for max purge threads.

max out parallel purge worker tasks, on slow shutdown, to speedup

When some expression of an INET6 data type involves conversion to INET6 from
other data types, e.g. in:

- CAST:

    SELECT CAST(non_inet6_expr AS INET6)

- CASE and hybrid functions:

    SELECT CASE WHEN expr THEN inet6_expr ELSE non_inet6_expr END

- UNION:

    SELECT inet6_expr UNION SELECT non_inet6_expr

the result column must be fixed as NULL-able even if the non-inet6 expression itself
is not NULL-able, because at the execution time the conversion can fail.

Details:
- Forcing NULL-ability if conversion from some data type to INET6 is involved
  (for non-constant or for expensive expressions).
- Non-expensive constant expressions are tested for NULL-ability at fix_fields() time,
  so things like `CAST('::' AS INET6)` are still detected as NOT NULL.
- Adding "bool warn" parameter into a few methods, to avoid redundant warnings
  at fix_fields() time when calculating NULL-ability of constant values.

fts_optimize_shutdown(): Wait for fts_optimize_callback()
to terminate before deleting the timer that it uses.

The buf_page_free() call that was introduced in MDEV-15528 was
performed too early in fseg_free_page(), tripping a debug check
in ibuf_remove_free_page(). In all other callers, we can (and will)
invoke buf_page_free() right after fseg_free_page(), but in
ibuf_remove_free_page() we will defer that call to the end of the
mini-transaction. (That call was already present.)