If the InnoDB buffer pool contains many pages for a table or index
that is being dropped or rebuilt, and if many of such pages are
pointed to by the adaptive hash index, dropping the adaptive hash index
may consume a lot of time.

The time-consuming operation of dropping the adaptive hash index entries
is being executed while the InnoDB data dictionary cache dict_sys is
exclusively locked.

It is not actually necessary to drop all adaptive hash index entries
at the time a table or index is being dropped or rebuilt. We can let
the LRU replacement policy of the buffer pool take care of this gradually.
For this to work, we must detach the dict_table_t and dict_index_t
objects from the main dict_sys cache, and once the last
adaptive hash index entry for the detached table is removed
(when the garbage page is evicted from the buffer pool) we can free
the dict_table_t and dict_index_t object.

Related to this, in MDEV-16283, we made ALTER TABLE...DISCARD TABLESPACE
skip both the buffer pool eviction and the drop of the adaptive hash index.
We shifted the burden to ALTER TABLE...IMPORT TABLESPACE or DROP TABLE.
We can remove the eviction from DROP TABLE. We must retain the eviction
in the ALTER TABLE...IMPORT TABLESPACE code path, so that in case the
discarded table is being re-imported with the same tablespace identifier,
the fresh data from the imported tablespace will replace any stale pages
in the buffer pool.

rpl.rpl_failed_drop_tbl_binlog: Remove the test. DROP TABLE can
no longer be interrupted inside InnoDB.

fseg_free_page(), fseg_free_step(), fseg_free_step_not_header(),
fseg_free_page_low(), fseg_free_extent(): Remove the parameter
that specifies whether the adaptive hash index should be dropped.

btr_search_lazy_free(): Lazily free an index when the last
reference to it is dropped from the adaptive hash index.

buf_pool_clear_hash_index(): Declare static, and move to the
same compilation unit with the bulk of the adaptive hash index
code.

dict_index_t::clone(), dict_index_t::clone_if_needed():
Clone an index that is being rebuilt while adaptive hash index
entries exist. The original index will be inserted into
dict_table_t::freed_indexes and dict_index_t::set_freed()
will be called.

dict_index_t::set_freed(), dict_index_t::freed(): Note that
or check whether the index has been freed. We will use the
impossible page number 1 to denote this condition.

dict_index_t::n_ahi_pages(): Replaces btr_search_info_get_ref_count().

dict_index_t::detach_columns(): Move the assignment n_fields=0
to ha_innobase_inplace_ctx::clear_added_indexes().
We must have access to the columns when freeing the
adaptive hash index. Note: dict_table_t::v_cols[] will remain
valid. If virtual columns are dropped or added, the table
definition will be reloaded in ha_innobase::commit_inplace_alter_table().

buf_page_mtr_lock(): Drop a stale adaptive hash index if needed.

We will also reduce the number of btr_get_search_latch() calls
and enclose some more code inside #ifdef BTR_CUR_HASH_ADAPT
in order to benefit cmake -DWITH_INNODB_AHI=OFF.

When neither MSAN nor Valgrind are enabled, declare
Field::mark_unused_memory_as_defined() as an empty inline function,
instead of declaring it as a virtual function.

This allows us to remove our own declarations of functions and structures
that are declared in the history.h file.

MDEV-22073 MSAN use-of-uninitialized-value in
collect_statistics_for_table()

Other things:
innodb.analyze_table was changed to mainly test statistic
collection. Was discussed with Marko.

The issue here was that when the schema was changed the value for the THD::server_status
is ored with SERVER_SESSION_STATE_CHANGED.
For custom aggregate functions, currently we check if the server_status is equal to
SERVER_STATUS_LAST_ROW_SENT then we should terminate the execution of the custom
aggregate function as there are no more rows to fetch.
So the check should be that if the server status has the bit set for
SERVER_STATUS_LAST_ROW_SENT then we should terminate the execution of the
custom aggregate function.

Other things:
- Removed innodb_encryption_tables.test from valgrind as it
  takes a REALLY long time

fix_fields_for_tvc() could call fix_fields() for Items that have
already been fixed before. Changing fix_fields() to fix_fields_if_needed().

On a checksum failure of a ROW_FORMAT=COMPRESSED page,
buf_LRU_free_one_page() would invoke buf_LRU_block_remove_hashed()
which will read the uncompressed page frame, although it would not
be initialized. With bad enough luck, fil_page_get_type(page)
could return an unrecognized value and cause the server to abort.

buf_page_io_complete(): On the corruption of a ROW_FORMAT=COMPRESSED
page, zerofill the uncompressed page frame.

This essentially reverts commit b393e2cb.

The leak might have been fixed, but because the
DEBUG_SYNC instrumentation for InnoDB purge threads was reverted
in 10.5 commit 5e62b6a5
as part of introducing a thread pool, it is easiest to revert
the entire change.

TRUNCATE(decimal_5_5) erroneously tried to create a DECIMAL(0,0) column.
Creating a DECIMAL(1,0) column instead.

MDEV-22503 MDB limits DECIMAL column precision to 16 doing CTAS with floor/ceil over DECIMAL(X,Y) where X > 16

The DECIMAL data type branch in Item_func_int_val::fix_length_and_dec()
incorrectly used DOUBLE-style length calculation, which resulted in
a smaller data type than the actual result of FLOOR()/CEIL() needs.

MDEV-19622 Assertion failures in
ha_partition::set_auto_increment_if_higher upon UPDATE on Aria
table

Flush LSN to system tablespace on innodb shutdown if XA is rolled back by
mariabackup.

innobase_get_charset(), innobase_get_stmt_safe(): Remove.
It is more efficient and readable to invoke thd_charset()
and thd_query_safe() directly, without a non-inlined wrapper function.

The function thd_query_safe() is used in the implementation of the
following INFORMATION_SCHEMA views:

    information_schema.innodb_trx
    information_schema.innodb_locks
    information_schema.innodb_lock_waits
    information_schema.rocksdb_trx

The implementation of the InnoDB views is in trx_i_s_common_fill_table().
This function invokes trx_i_s_possibly_fetch_data_into_cache(),
which will acquire lock_sys->mutex and trx_sys->mutex in order to
protect the set of active transactions and explicit locks.
While holding those mutexes, it will traverse the collection of
InnoDB transactions. For each transaction, thd_query_safe() will be
invoked.

When called via trx_i_s_common_fill_table(), thd_query_safe()
is acquiring THD::LOCK_thd_data while holding the InnoDB locks.
This will cause a deadlock with THD::awake() (such as executing
KILL QUERY), because THD::awake() could invoke lock_trx_handle_wait(),
which attempts to acquire lock_sys->mutex while already holding
THD::lock_thd_data.

thd_query_safe(): Invoke mysql_mutex_trylock() instead of
mysql_mutex_lock(). Return the empty string if the mutex
cannot be acquired without waiting.

As part of the SPATIAL INDEX implementation in InnoDB,
dict_index_t was expanded by a rtr_ssn_t field. There are only
3 operations for this field, all protected by rtr_ssn_t::mutex:

* btr_cur_search_to_nth_level() stores the least significant 32 bits
of the 64-bit value that is stored in the index root page.
(This would better be done when the table is opened for the
very first time.)
* rtr_get_new_ssn_id() increments the value by 1.
* rtr_get_current_ssn_id() reads the current value.

All these operations can be implemented equally safely by using
atomic memory access operations.