Problem was that we skipped background persistent statistics calculation
on applier nodes if thread is marked as high priority (a.k.a BF).
However, on applier nodes all DDL which is replicate will be executed
as high priority i.e BF.

Fixed by allowing background persistent statistics calculation on
applier nodes even when thread is marked as BF. This could lead
BF lock waits but for queries on that node needs that statistics.

Removed redundant plugin_thdvar_cleanup() from end_connection(): called by
THD::free_connection(), which always follows end_connection().

Saves at least one lock(LOCK_plugin) and one
rdlock(LOCK_system_variables_hash).

Benchmarked on a 2socket/20core/40threads Broadwell system using sysbench
connect brencmark @40 threads (with select 1 disabled).

10.2 shows moderate improvement: 136219.93 -> 137766.31 CPS.
10.3 is improvement is somewhat better: 93018.29 -> 101379.77 CPS.

Also backported MyRocks memory leak fix from 10.4, which turned out to
be unrelated.

We do want to ignore InnoDB's internal #sql-ib*.ibd at shutdown,
because those tables will be dropped on the next startup.
Failure to filter out these table names occasionally causes some
unwanted output for tests that restart InnoDB soon after dropping
or truncating tables, for example innodb.recovery_shutdown.

This also fixes -Wstringop-truncation that GCC 8 issued for strncpy().

MDEV-18502: Server crash in find_field_in_tables upon 2nd execution of SP which causes ER_WRONG_GROUP_FIELD

Fixed by the commit cb11b3fb.
Adding the test case for this issue.

The issue here was when we had a subquery and a window function in an expression in
the select list then subquery was getting computed after window function computation.
This resulted in incorrect results because the subquery was correlated and the fields
in the subquery was pointing to the base table instead of the temporary table.

The approach to fix this was to have an additional field in the temporary table
for the subquery and to execute the subquery before window function execution.
After execution the values for the subquery were stored in the temporary table
and then when we needed to calcuate the expression, all we do is read the values
from the temporary table for the subquery.

recv_parse_log_recs(): Do not compare type if ptr==end_ptr
(we have reached the end of the redo log parsing buffer),
because it will not have been correctly initialized in that case.

GCC 6 and later can optimize away the memset() that is part of
mem_heap_zalloc() in a placement new call. So, instead of relying
on that kind of initialization, explicitly initialize the necessary
fields in the constructors.

que_common_t::que_common_t(): Initialize more fields in the
default constructor.

purge_vcol_info_t::purge_vcol_info_t(): Initialize all fields in
the default constructor.

purge_node_t::purge_node_t(): Initialize all necessary fields.

Reference:

    https://gcc.gnu.org/bugzilla/show_bug.cgi?id=71388

    https://gcc.gnu.org/ml/gcc/2016-02/msg00207.html

row_merge_create_fts_sort_index(): Initialize dict_col_t in
an unambiguous way. GCC 6 and later appear to be able to optimize
away the memset() that is part of mem_heap_zalloc() in the
placement new call. Let us avoid using placement new in order
to ensure that the objects will actually be initialized.

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=71388

https://gcc.gnu.org/ml/gcc/2016-02/msg00207.html

While the latter reference hints that the optimization is only
applicable to non-POD types (and dict_col_t does not define
any member functions before 10.2), it is most consistent to
use the same initialization across all versions.

MDEV-17070 Table corruption or Assertion `table->file->stats.records > 0 || error' or Assertion `!is_set() || (m_status == DA_OK_BULK && is_bulk_op())' failed upon actions on temporary table

This was caused by a combination of factors:
* MyISAM/Aria temporary tables historically never saved the state
  to disk (MYI/MAI), because the state never needed to persist
* certain ALTER TABLE operations modify the original TABLE structure
  and if they fail, the original table has to be reopened to
  revert all changes (m_needs_reopen=1)

as a result, when ALTER fails and MyISAM/Aria temp table gets reopened,
it reads the stale state from the disk.

As a fix, MyISAM/Aria tables now *always* write the state to disk
on close, *unless* HA_EXTRA_PREPARE_FOR_DROP was done first. And
the server now always does HA_EXTRA_PREPARE_FOR_DROP before dropping
a temporary table.

JSON_ARRAY and JSON_OBJECT functions with no arguments now get the
connection charset. Item_func_convert_charset returns the correct
is_json() flag.

ALTER TABLE ... ADD FOREIGN KEY may trigger assertion failure when
it has LOCK=EXCLUSIVE clause or concurrent FLUSH TABLES is being
executed.

In both cases being altered table is marked as flushed, which forces
subsequent attempt to open parent table to re-open. Which in turn is
not allowed while transaction is running.

Rather than opening parent table, just take appropriate MDL lock.

Also removed table_already_fk_prelocked() check: MDL itself has much
better methods to handle duplicate locks. E.g. the former won't acquire
MDL_SHARED_NO_WRITE if it already has MDL_SHARED_READ.

Initialize node->trx_id before checking if a table can be skipped.

wait_all_purged.inc: Wait for 60 seconds instead of 30 seconds.
Purge can be slow on buildbot, especially in ASAN-instrumented builds.

purge_node_t::in_progress: Replaces purge_node_t::done.
Only present in debug builds.

purge_node_t::start(): Moved from the start of row_purge_step().

purge_node_t::end(): Replaces row_purge_end().

trx_purge_attach_undo_recs(): Omit a check from non-debug builds.

If a table has been dropped, rebuilt, or its tablespace has been
discarded or the table is corrupted, it does not make sense to
look up that table again while purging old undo log records.

purge_node_t::purge_node_t(): Replaces row_purge_node_create().

que_common_t::que_common_t(): Constructor.

row_import_update_index_root(): Remove the constant parameter
dict_locked=true, and update the table->def_trx_id in the cache.

purge_node_t::unavailable_table_id: The latest unavailable table ID,
to avoid future lookups.

purge_node_t::def_trx_id: The latest modification of the table
identified by unavailable_table_id, or TRX_ID_MAX.

purge_node_t::is_skipped(): Determine if a table should be skipped.

purge_node_t::skip(): Note that a table should be skipped.

This can be useful:
UBSAN_OPTIONS=log_path=/some/path

clang users may want to increase stack size in include/my_pthread.h or enable
some optimizations

Clean up after commit 0957d257
which introduced some disorder (unsorted or duplicated test names).

modified:   suite/galera/t/galera_autoinc_sst_mariabackup.test

remove WSREP_SST_OPT_SUFFIX_VALUE, checking [mysqld] is covered in the parse_cnf --mysqld case also in wsrep_sst_xtrabackup-v2

wsrep_sst: remove WSREP_SST_OPT_SUFFIX_VALUE, checking [mysqld] is covered in the parse_cnf --mysqld case

modified:   mysql-test/suite/galera/disabled.def
modified:   mysql-test/suite/galera/r/galera_many_rows.result
modified:   mysql-test/suite/galera/t/galera_kill_nochanges.test
new file:   mysql-test/suite/galera/t/galera_many_rows.cnf
modified:   mysql-test/suite/galera/t/galera_many_rows.test
modified:   mysql-test/suite/galera/t/galera_var_dirty_reads.test
modified:   scripts/wsrep_sst_mariabackup.sh

galera.partition and galera.galera_binlog_stmt_autoinc regularly display
mismatching values for AUTO_INCREMENT columns.

galera.MW-336 often times out while waiting for something in PROCESSLIST.

Also, sort the test names, remove the redundant "galera." prefix and
fix typos in 2 test names.

- Fetch innodb_compression_level from the running server.Add the value
of innodb_compression_level in backup-my.cnf file during backup phase.
So that prepare can use the innodb_compression_level variable from
backup-my.cnf

The 10.1 changes to the test case were accidentally omitted
in the merge commit 913e33e4.

The test case was accidentally omitted from the merge
commit 913e33e4.

GCC does not like MY_ATTRIBUTE((nonnull)) on a reference-to-pointer
parameter. clang did not flag an issue wit that.

Rewrite the MDEV-13818 fix to prevent heap-use-after-free.

Add a test case for MDEV-18272.

row_merge_create_index_graph(): Relay the internal state
from dict_create_index_step(). Our caller should free the index
only if it was not copied, added to the cache, and freed.

row_merge_create_index(): Free the index template if it was
not added to the cache. This is a safer variant of the logic
that was introduced in 65070bef in 10.2.

prepare_inplace_alter_table_dict(): Add additional fault injection
to exercise a code path where we have already added an index
to the cache.