Number of jobs dropped from 23 -> 17 and build time from 8-10 hours to
3-4 hours.

Drop GCC 6 and Clang 6 from build dependencies and version 6 is dropped
from the jobs matrix.

Also ignore arm64 and ppc64le on Bionic builds since they sporadically
fail.

innodb_buffer_pool_evict_uncompressed(): Remove the mutex acquisition
that was inadvertently added in 1a6f708e.

In MDEV-12353, the calls to mtr_t::memo_modify_page()
were accidentally removed along with
mlog_open_and_write_index() and its callers.

Let us resurrect the function to enable better debug checks.

mtr_t::flag_modified(): Renamed from mtr_t::set_modified()
and made private.

mtr_t::set_modified(): Take const buf_block_t& as a parameter.

In several mtr_t member functions, replace const buf_page_t&
parameters with const buf_block_t&, so that we can pass the
parameter to set_modified().

mtr_t::modify(): Add a MTR_MEMO_MODIFY entry for a block that
is guaranteed to be modified in the mini-transaction.

page_zip_clear_rec(): Explicitly initialize len
in non-debug builds to avoid a warning about possibly
invalid memset() length.

copy_keys_from_share(): Use reinterpret_cast instead of
manipulating a reference to a type-punned pointer.

This cleans up after the cleanup
commit 0515577d.

In commit a5584b13
some scrubbing-related status variables were removed along with
the background scrubbing code.
The status variable INNODB_ENCRYPTION_NUM_KEY_REQUESTS
was inadvertently removed as part of that.

innodb_status_variables[]: Restore "encryption_num_key_requests".

We introduce the test innodb.innodb_status_variables
in order to catch similar regressions in the future.

Because InnoDB is not freeing undo pages to the normal
free-page management, old undo log pages can be reused. Due to that,
it is possible (but unlikely) that the fields TRX_UNDO_NEEDS_PURGE
and TRX_UNDO_LOG_START relative to the free offset that is stored at
TRX_UNDO_PAGE_HDR + TRX_UNDO_PAGE_START already have the correct value.
Hence, we must pass the mtr_t::OPT template parameter to silence the
debug assertion.

Other writes in trx_undo_header_create() that are using the default
template parameter seem to be correct (the data fields should be
guaranteed to change even in the event of reusing pages).

that is don't call alloc_lookup_buffer() and create_lookup_handler()
for every row

also, don't call ha_check_overlaps() for every partition,
after it was already done on the ha_partition level

* 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.