* The overlaps check is implemented on a handler level per row command.
  It creates a separate cursor (actually, another handler instance) and
  caches it inside the original handler, when ha_update_row or
  ha_insert_row is issued. Cursor closes on unlocking the handler.

* Containing the same key in index means unique constraint violation
  even in usual terms. So we fetch left and right neighbours and check
  that they have same key prefix, excluding from the key only the period part.
  If it doesnt match, then there's no such neighbour, and the check passes.
  Otherwise, we check if this neighbour intersects with the considered key.

* The check does not introduce new error and fails with ER_DUPP_KEY error.
  This might break REPLACE workflow and should be fixed separately

* rename to a generic name
* move remaning initializations from query exec to prepare time
* simplify/unify key handling in open_table_from_share and delayed
* remove dead code
* move tests where they belong

key_copy is supposed to take field values from the from_record
argument, but it was mostly ignoring it and instead relying on the
caller to set field->ptr pointers accordingly. Inconsistently,
it was checking the null bitmap in the from_record, not
at the field->null_ptr.

Now key_copy correctly takes all field values from the from_record.

Sergei's commit ac6b3c44 implemented handler status counters
compensation for underlying handlers like ha_partition.
`index_read_idx_map` is missing there, but it should have been fixed as
well (proof: ha_partition::index_read_idx_map never calls
ha_partition::index_read_map).

Note: all this compensation logic could be broken for subpartitions! (We
can experience double decrement)

Remove special treatment for Aria.
Add a test with --help and mysql.plugin table being InnoDB

MyISAM is still treated specially, as we need to be able
to initialize global_system_variables.table_plugin reliably

where PK is neither required nor implied

When MDEV-19514 removed the change buffer merges in the background,
it introduced a minor regression: After a DDL operation that drops
or rebuilds a table or partition, any entries in the change buffer
could survive until a slow shutdown (innodb_fast_shutdown=0) is executed.

fil_delete_tablespace(). Before returning, invoke
ibuf_delete_for_discarded_space(). With this, the only way to have
change buffer ‘leaks’ is to kill and restart the server at an
appropriate moment and never initiate a slow shutdown.

There is no background change buffer merge any more.
Change buffer merge will only take place during a slow shutdown
(a shutdown initiated after SET GLOBAL innodb_fast_shutdown=0).

The definition of the member function ha_cassandra::records_in_range()
was inadvertently removed (renamed to a non-member function) in
commit ff64152b.

Let us define the overridden member function inline, and add C++11
override qualifiers.

recv_sys.recovery_on: Replaces recv_recovery_on.

recv_sys_t::apply(): Replaces recv_apply_hashed_log_recs().

recv_sys_var_init(): Remove.

recv_sys_t::recover_low(): Attempt to initialize a page based
on buffered redo log records.

In commit f8a9f906
we removed support for crash-upgrade from older versions,
but forgot to remove a check for recovering TRUNCATE TABLE
if MariaDB 10.2.18 or 10.3.9 or earlier were killed and
we are attempting to upgrade to MariaDB 10.5.2 or later.
Already MariaDB 10.4 would refuse to recover such TRUNCATE
operations.

If a table is altered using the MDEV-11369/MDEV-15562/MDEV-13134
ALGORITHM=INSTANT, it can force the table to use a non-canonical
format:

* A hidden metadata record at the start of the clustered index
is used to store each column's DEFAULT value. This makes it possible
to add new columns that have default values without rebuilding the table.

* Starting with MDEV-15562 in MariaDB Server 10.4, a BLOB in the
hidden metadata record is used to store column mappings. This makes
it possible to drop or reorder columns without rebuilding the table.
This also makes it possible to add columns to any position or drop
columns from any position in the table without rebuilding the table.

If a column is dropped without rebuilding the table, old records
will contain garbage in that column's former position, and new records
will be written with NULL values, empty strings, or dummy values.

This is generally not a problem. However, there may be cases where
users may want to avoid putting a table into this format.
For example, users may want to ensure that future UPDATE operations
after an ADD COLUMN will be performed in-place, to reduce write
amplification. (Instantly added columns are essentially always
variable-length.) Users might also want to avoid bugs similar to
MDEV-19916, or they may want to be able to export tables to
older versions of the server.

We will introduce the option innodb_instant_alter_column_allowed,
with the following values:

* never (0): Do not allow instant add/drop/reorder,
to maintain format compatibility with MariaDB 10.x and MySQL 5.x.
If the table (or partition) is not in the canonical format, then
any ALTER TABLE (even one that does not involve instant column
operations) will force a table rebuild.

* add_last (1, default in 10.3): Store a hidden metadata record that
allows columns to be appended to the table instantly (MDEV-11369).
In 10.4 or later, if the table (or partition) is not in this format,
then any ALTER TABLE (even one that does not involve column changes)
will force a table rebuild.

Starting with 10.4:

* add_drop_reorder (2, default): Like 'add_last', but allow the
metadata record to store a column map, to support instant
add/drop/reorder of columns (MDEV-15562).

		partition does rebuild

- In ha_innobase::commit_inplace_alter_table() assumes that all partition
should do the same kind of alter operations. During DDL, if one partition
requires table rebuild and other partition doesn't need rebuild
then all partition should be forced to rebuild.

MDEV-22019: Sig 11 in next_breadth_first_tab | max_sort_length setting + double GROUP BY leads to crash

No need to create a temp table for aggregation if we have encountered some error.

For ENGINE=Aria, we work around bugs in various tests that catch
writes of uninitialized bytes from the Aria page cache.
(Why do we even write anything on DROP TABLE?)

MemorySanitizer (clang -fsanitize=memory) requires that all code
be compiled with instrumentation enabled. The C runtime library
is an exception. Failure to use instrumented libraries will cause
bogus messages about memory being uninitialized.

In WITH_MSAN builds, we must avoid calling getservbyname(),
because even though it is a standard library function, it is
not instrumented, not even in clang 10.

The following cmake options were tested:

-DCMAKE_C_FLAGS='-march=native -O2'
-DCMAKE_CXX_FLAGS='-stdlib=libc++ -march=native -O2'
-DWITH_EMBEDDED_SERVER=OFF -DWITH_UNIT_TESTS=OFF -DCMAKE_BUILD_TYPE=Debug
-DWITH_INNODB_{BZIP2,LZ4,LZMA,LZO,SNAPPY}=OFF
-DPLUGIN_{ARCHIVE,TOKUDB,MROONGA,OQGRAPH,ROCKSDB,CONNECT,SPIDER}=NO
-DWITH_SAFEMALLOC=OFF
-DWITH_{ZLIB,SSL,PCRE}=bundled
-DHAVE_LIBAIO_H=0
-DWITH_MSAN=ON

MEM_MAKE_DEFINED(): An alias for VALGRIND_MAKE_MEM_DEFINED()
and in the future, __msan_unpoison().

For now, neither MEM_MAKE_DEFINED() nor MEM_UNDEFINED()
perform any action under MSAN. Enabling them will catch more bugs, but
will also require some more fixes or work-arounds.

Json_writer::add_double(): Work around a frequently occurring
failure in optimizer tests, related to EXPLAIN FORMAT=JSON.

dtoa(): Disable MSAN altogether. For some reason, this function
is triggering a lot of trouble, especially when invoked for
DBUG functions. The MDL default timeout is dd=86400 seconds,
and for some reason it is claimed to be uninitialized.

InnoDB: Define UNIV_DEBUG_VALGRIND also WITH_MSAN.

ut_crc32_8_hw(), ut_crc32_64_low_hw(): Use the compiler built-in
functions instead of inline assembler when building WITH_MSAN.
This will require at least -msse4.2 when building for IA-32 or AMD64.
The inline assembler would not be instrumented, and would thus cause
bogus failures.

Valgrind only seems to complain about memcmp() operations that
actually end up reading uninitialized data, while MemorySanitizer
requires that the entire length of both buffers be defined.

Rework stats a bit, so we're not missing any queue_get() now.

Don't do stats_reset_table(), if generic threadpool is off.

During the test main.query_cache_innodb, only 16 bytes of
db_buf are initialized during the memcmp() in
dict_acquire_mdl_shared<false>(), but db_len was wrongly set to 20 bytes.

Something similar was fixed in MDEV-21344, but only for the table name,
in commit 0e25a8b4.

dict_table_t::parse_name(): Assign the return value of
filename_to_tablename() to the output parameters for lengths.
There is no need to invoke strlen().

With OpenSSL < 1.1 there is a potential for a race condition to occur.
This can cause the S3 engine to crash. The workaround is to add locking
callbacks to OpenSSL so that this doesn't happen.

https://curl.haxx.se/libcurl/c/threadsafe.html

There is a fix in libMariaS3 for this which when a certain flag is set
(HAVE_CURL_OPENSSL_UNSAFE) will add the required locks.

This patch adds CMake support so that the flag is set if it is found
that Curl is compiled with an unsafe OpenSSL version. For example Ubuntu
16.04 with libcurl4-openssl-dev.

- Updated icp_tests.inc and result files
- Updates usage of records_in_range() protype in cassandra

page_cur_insert_rec_low(): Remove a bogus condition that wrongly
omitted redo logging when the record contains no data payload bytes.
We can have such records in secondary indexes, when the values of
the PRIMARY KEY column(s) are the empty string, and the values of
secondary key column(s) are are NULL or the empty string.

page_apply_delete_dynamic(): Improve the consistency check, and
do not allow adjacent records to be less than 5 bytes apart from
each other. The fixed-size part of the record header is 5 bytes.
Usually there must also be some header or payload bytes, but in
an extreme case where all columns are CHAR(0) NOT NULL, the
minimum secondary index record size is 5 bytes, and the table can
contain at most 1 row. The minimum clustered index record size is
5+6+7 bytes (header, DB_TRX_ID, DB_ROLL_PTR) or x+5+4 bytes
(fixed-size header, child page number, and some additional header
or payload bytes).

- multi_range_read_info_const now uses the new records_in_range interface
- Added handler::avg_io_cost()
- Don't calculate avg_io_cost() in get_sweep_read_cost if avg_io_cost is
  not 1.0.  In this case we trust the avg_io_cost() from the handler.
- Changed test_quick_select to use TIME_FOR_COMPARE instead of
  TIME_FOR_COMPARE_IDX to align this with the rest of the code.
- Fixed bug when using test_if_cheaper_ordering where we didn't use
  keyread if index was changed
- Fixed a bug where we didn't use index only read when using order-by-index
- Added keyread_time() to HEAP.
  The default keyread_time() was optimized for blocks and not suitable for
  HEAP. The effect was the HEAP prefered table scans over ranges for btree
  indexes.
- Fixed get_sweep_read_cost() for HEAP tables
- Ensure that range and ref have same cost for simple ranges
  Added a small cost (MULTI_RANGE_READ_SETUP_COST) to ranges to ensure
  we favior ref for range for simple queries.
- Fixed that matching_candidates_in_table() uses same number of records
  as the rest of the optimizer
- Added avg_io_cost() to JT_EQ_REF cost. This helps calculate the cost for
  HEAP and temporary tables better. A few tests changed because of this.
- heap::read_time() and heap::keyread_time() adjusted to not add +1.
  This was to ensure that handler::keyread_time() doesn't give
  higher cost for heap tables than for normal tables. One effect of
  this is that heap and derived tables stored in heap will prefer
  key access as this is now regarded as cheap.
- Changed cost for index read in sql_select.cc to match
  multi_range_read_info_const(). All index cost calculation is now
  done trough one function.
- 'ref' will now use quick_cost for keys if it exists. This is done
  so that for '=' ranges, 'ref' is prefered over 'range'.
- scan_time() now takes avg_io_costs() into account
- get_delayed_table_estimates() uses block_size and avg_io_cost()
- Removed default argument to test_if_order_by_key(); simplifies code

Fixed by moving testing of get_best_group_min_max() after range testing.

Prototype change:
-  virtual ha_rows records_in_range(uint inx, key_range *min_key,
-                                   key_range *max_key)
+  virtual ha_rows records_in_range(uint inx, const key_range *min_key,
+                                   const key_range *max_key,
+                                   page_range *res)

The handler can ignore the page_range parameter. In the case the handler
updates the parameter, the optimizer can deduce the following:
- If previous range's last key is on the same block as next range's first
  key
- If the current key range is in one block
- We can also assume that the first and last block read are cached!
  This can be used for a better calculation of IO seeks when we
  estimate the cost of a range index scan.

The parameter is fully implemented for MyISAM, Aria and InnoDB.
A separate patch will update handler::multi_range_read_info_const() to
take the benefits of this change and also remove the double
records_in_range() calls that are not anymore needed.