svr_n_page_hash_locks: Increase from 16 to 64. Before MDEV-15058,
we used to have the buf_pool.page_hash partitioned to each instance.

rw_lock_lock_word_decr(): Sleep a little in the spinloop.

rw_lock_s_lock_low(): Correct a comment. The function does perform
spinning.

This improves scalability in read-only workloads on a 32-CPU system
when the number of concurrent connections exceeds the CPU core count.

Thanks to Axel Schwenke for running benchmarks.

The issue here is charset for Sort_param::tmp_buffer is cleared when bzero is done for Sort_param.
Make sure to set the charset explicitly in the constructor for tmp_buffer.

reduce the amount of engine-specific code in the server,
particularly as it does not serve any purpose now.

may be needed for VP engine,
to be reconsidered in MDEV-7795

Disallow BIT_AND(), BIT_OR(), BIT_XOR() for data types GEOMETRY and INET6,
as they cannot return any useful integer values.

MDEV-22325 ib_logfile0 is too small for innodb_thread_concurrency=0. The size of ib_logfile0 should be bigger than 200 kB * innodb_thread_concurrency.

Correct log message. IMO, we shouldn't be very precise in that
message as the formula behind it is not trivial.

Also performed a little cleanup.

buf_LRU_make_block_young(): Merge with buf_page_make_young().

buf_pool_check_no_pending_io(): Remove. Replaced with
buf_pool.any_io_pending() and buf_pool.io_pending(),
which do not unnecessarily acquire buf_pool.mutex.

buf_pool_t::init_flush[]: Use atomic access, so that
buf_flush_wait_LRU_batch_end() can avoid acquiring buf_pool.mutex.

buf_pool_t::try_LRU_scan: Declare as bool.

When MDEV-22769 introduced srv_shutdown_state=SRV_SHUTDOWN_INITIATED in
commit efc70da5
we forgot to adjust a few checks for SRV_SHUTDOWN_NONE.

In the initial shutdown step, we are waiting for the background
DROP TABLE queue to be processed or discarded. At that time,
some background tasks (such as buffer pool resizing or dumping
or encryption key rotation) may be terminated, but others must
remain running normally.

srv_purge_coordinator_suspend(), srv_purge_coordinator_thread(),
srv_start_wait_for_purge_to_start(): Treat SRV_SHUTDOWN_NONE
and SRV_SHUTDOWN_INITIATED equally.

dict_table_t::parse_name(): Strip any partition or subpartition
name before copying the name to the decoding buffer.

MDEV-19320 Sequence gets corrupted and produces ER_KEY_NOT_FOUND
           (Can't find record) after ALTER .. ORDER BY

MDEV-19977 Assertion `(0xFUL & mode) == LOCK_S ||
           (0xFUL & mode) == LOCK_X' failed in lock_rec_lock

create_table_info_t::create_foreign_keys(): Make the create_name buffer
long enough for both the database and table name. It is still not long
enough to hold partition or subpartition names. Because we do never
supported FOREIGN KEY constraints on partitions, we can simply skip
the call to innobase_convert_name() on CREATE TABLE.

MDEV-22719 Long unique keys are not created when individual key_part->length < max_key_length but SUM(key_parts->length) > max_key_length

Make UNIQUE HASH key in case when key_info->key_length > max_key_length

MDEV-21804 Assertion `marked_for_read()' failed upon INSERT into table with long unique blob under binlog_row_image=NOBLOB

Problem:- Calling mark_columns_per_binlog_row_image() earlier may change the
result of mark_virtual_columns_for_write() , Since it can set the bitmap on
for virtual column, and henceforth  mark_virtual_column_deps(field) will
never be called in mark_virtual_column_with_deps.

This bug is not specific for long unique, It also fails for this case
   create table t2(id int primary key, a blob, b varchar(20) as (LEFT(a,2)));

This bug is the same as the bug MDEV-17024. The crashes caused by these
bugs were due to premature cleanups of the unit specifying recursive CTEs
that happened in some cases when there were several outer references the
same recursive CTE.
The problem of premature cleanups for recursive CTEs could be already
resolved by the correction in TABLE_LIST::set_as_with_table() introduced
in this patch. ALL other changes introduced by the patches for MDEV-17024
and MDEV-22748 guarantee that this clean-ups are performed as soon as
possible: when the select containing the last outer reference to a
recursive CTE is being cleaned up the specification of the recursive CTE
should be cleaned up as well.

lock_check_trx_id_sanity(): Because the argument of UNIV_LIKELY
or __builtin_expect() can be less than sizeof(trx_id_t) on 32-bit
systems, it cannot reliably perform an implicit comparison to 0.

Bit operators (~ ^ | & << >>) and the function BIT_COUNT()
always called val_int() for their arguments.
It worked correctly only for INT type arguments.

In case of DECIMAL and DOUBLE arguments it did not work well:
the argument values were truncated to the maximum SIGNED BIGINT value
of 9223372036854775807.

Fixing the code as follows:

- If the argument if of an integer data type,
  it works using val_int() as before.

- If the argument if of some other data type, it gets the argument value
  using val_decimal(), to avoid truncation, and then converts the result
  to ulonglong.

Using Item_handled_func to switch between the two approaches easier.

As an additional advantage, with Item_handled_func it will be easier
to implement overloading in the future, so data type plugings will be able
to define their own behavioir of bit operators and BIT_COUNT().

Moving the code from the former val_int() implementations
as methods to Longlong_null, to avoid code duplication in the
INT and DECIMAL branches.

page_zip_fields_decode(): Do not dereference index=NULL.
Instead, return NULL early. The only caller does not care
about the values of output parameters in that case.

This bug was introduced in MySQL 5.7.6 by
mysql/mysql-server@9eae0edb7a8e4004328e61157f5f3b39cebe1b2b
and in MariaDB 10.2.2 by
commit 2e814d47.

Thanks to my son for pointing this out after investigating
the output of a static analysis tool.

fil_aio_callback(): Remove a bogus assertion that was added in
commit b1ab211d (MDEV-15053).
We will have !bpage for any write by buf_flush_freed_page().

buf_page_init_for_read(): Initialize the output parameter of
buf_buddy_alloc().

Compiler tells something about argument-dependent lookup. I do not
understand how that ADL works. But I know that such operators should
be free functions, instead of methods:
http://isocpp.github.io/CppCoreGuidelines/CppCoreGuidelines#Ro-symmetric

Such syntax defines 'friend' free functions.

When processing a query with a recursive CTE a temporary table is used for
each recursive reference of the CTE. As any temporary table it uses its own
mem-root for table definition structures. Due to specifics of the current
implementation of ANALYZE stmt command this mem-root can be freed only at
the very of query processing. Such deallocation of mem-root memory happens
in close_thread_tables(). The function looks through the list of the tmp
tables rec_tables attached to the THD of the query and frees corresponding
mem-roots. If the query uses a stored function then such list is created
for each query of the function. When a new rec_list has to be created the
old one has to be saved and then restored at the proper moment.
The bug occurred because only one rec_list for the query containing CTE was
created. As a result close_thread_tables() freed tmp mem-roots used for
rec_tables prematurely destroying some data needed for the output produced
by the ANALYZE command.