Other usage if persistent statistics is checking 'stats_is_read' in
caller, which is why this was not noticed earlier.

Other things:
- Simplified no_stat_values_provided

srv_all_undo_tablespaces_open(): While opening the extra unused
undo tablespaces, InnoDB should use ULINT_UNDEFINED instead of
SRV_SPACE_ID_UPPER_BOUND.

recv_recovery_from_checkpoint_start(): InnoDB should add the
redo log block header + trailer size while checking the	log
sequence number in log file with log sequence number in the
system tablespace first page.

In commit 384eb570 the debug check
was relaxed in trx_undo_header_create(), not in the intended function
trx_undo_write_xid().

fil_aio_callback(): Invoke fil_node_t::complete_write() before
releasing any page latch, so that in case a log checkpoint is
executed roughly concurrently with the first write into a file
since the previous checkpoint, we will not miss a fdatasync()
or fsync() call to make the write durable.

In MemorySanitizer builds of 10.10 and 10.11, we would rather often
have the assertion fail in innodb_init() during mariadb-backup --prepare.
The assertion could also fail during InnoDB startup, but less often.

Before commit 685d958e in 10.8 the
log file cleanup after a successfully applied backup is different,
and the os_aio_pending_writes() assertion is in srv0start.cc.

IORequest::write_complete(): Invoke node->complete_write() before
releasing the page latch, so that a log checkpoint that is about to
execute concurrently will not miss a fdatasync() or fsync() on the
file, in case this was the first write since the last such call.

create_log_file(), srv_start(): Replace the debug assertion with
a debug check. For all intents and purposes, all writes could have
been completed but some write_io_callback() may not have invoked
io_slots::release() yet.

Problem:
========
- InnoDB fails to open undo tablespace when page0 is corrupted
and fails to throw error.

Solution:
=========
- InnoDB throws DB_CORRUPTION error when InnoDB encounters
page0 corruption of undo tablespace.

- InnoDB restores the page0 of undo tablespace from
doublewrite buffer if it encounters page corruption

- Moved Datafile::restore_from_doublewrite() to
recv_dblwr_t::restore_first_page(). So that undo
tablespace and system tablespace can use this function
instead of duplicating the code

srv_undo_tablespace_open(): Returns 0 if file doesn't exist
or ULINT_UNDEFINED if page0 is corrupted.

- InnoDB fails to check the overflow buffer while applying
the operation to the table that was rebuilt. This is caused
by commit 3cef4f8f (MDEV-515).

Fixed missing initialization of Alter_info()

This could cause crashes in some create table like scenarios
where some generated indexes where automatically dropped.

I also added a test that we do not try to drop from index_stats for
temporary tables.

The intentention was always to not create histograms for single value
unique keys (as histograms is not useful in this case), but because of
a bug in the code this was still done.

The changes in the test cases was mainly because hist_size is now NULL
for these kind of columns.

This reverts commit 03c9a4ef.

The fix is wrong. It was doing this: if the uninitialized
wait->m_class has some specific value, then don't initialize it.

MDEV-32272 lock_release_on_prepare_try() does not release lock if supremum bit is set along with other bits set in lock's bitmap

The error is caused by MDEV-30165 fix with the following commit:
d13a57ae

There is logical error in lock_release_on_prepare_try():

        if (supremum_bit)
          lock_rec_unlock_supremum(*cell, lock);
        else
          lock_rec_dequeue_from_page(lock, false);

Because there can be other bits set in the lock's bitmap, and the lock
type can be suitable for releasing criteria, but the above logic
releases only supremum bit of the lock.

The fix is to release lock if it suits for releasing criteria and unlock
supremum if supremum is locked otherwise.

Tere is also the test for the case, which was reported by QA team. I
placed it in a separate files, because it requires debug build.

Reviewed by: Marko Mäkelä

MDEV-31098  InnoDB Recovery doesn't display encryption message when no encryption configuration passed

- InnoDB fails to report the error when encryption configuration
wasn't passed. This patch addresses the issue by adding
the error while loading the tablespace and deferring the
tablespace creation.

Review cleanups.

There are many filesystem related errors that can occur with
MariaBackup. These already outputed to stderr with a good description of
the error. Many of these are permission or resource (file descriptor)
limits where the assertion and resulting core crash doesn't offer
developers anything more than the log message. To the user, assertions
and core crashes come across as poor error handling.

As such we return an error and handle this all the way up the stack.

This fixes up a merge of commit 4fb8f7d0
with respect to commit ea37b144.

The problem was that RANGE_OPT_PARAM was not completely initialized in
some cases.
Added bzero() to ensure that all elements are always initialized.

Fixed hang when renaming index to original name

Use Dummy_error_handler in open_stat_tables() to ignore all errors
when opening statistics tables.

Part of the test did not work with view_protocol as the query written
to the slow_log table is changed because of view_protocol.

There where several reasons why the test failed:
- Constructors for Field_double and Field_float changed an argument
  to the constructor instead of a the correct class variable.
- gcc 7.5.0 produced wrong code when inlining Field_double constructor
  into Field_test_double constructor.

Fixed by changing the correct class variable and make the constructors
not inline to go around the gcc bug.

In commit 5ea5291d @sanja-byelkin for unknown reason switched the file mode
for 3 Galera tzinfo related test files from 644 -> 755. This exists only
from branch 10.6 onward:

    $ git checkout 10.5
    $ find mysql-test -executable -name *.test -or -executable -name *.result
    (no results)
    $ git checkout 10.6
    $ find mysql-test -executable -name *.test -or -executable -name *.result
    mysql-test/suite/galera/t/mysql_tzmysql-test/suite/galera/t/mysql_tzinfo_to_sql.test
    mysql-test/suite/galera/t/mariadb_tzinfo_to_sql.test
    mysql-test/suite/galera/r/mariadb_tzinfo_to_sql.resultinfo_to_sql.test

mysql-test/suite/galera/t/mariadb_tzinfo_to_sql.test
mysql-test/suite/galera/r/mariadb_tzinfo_to_sql.result

No test file nor test result file should be executable, so run chmod -x
on them.

All new code of the whole pull request, including one or several files
that are either new files or modified ones, are contributed under the
BSD-new license. I am contributing on behalf of my employer Amazon Web
Services, Inc.

The bug was in the test case.
The problem was that maria_empty_logs.inc deleted aria log files before
the server was properly shutdown.
Fixed by waiting for pid file to disappear before starting to delete log
files.

Other things:
- Fixed that translog_purge_at_flush() will not stop deleting files even
  if one file could not be deleted.

The problem was that sometimes InnoDB returned sligtly wrong record count
for table, which causes the optimizer to disregard the result from
the range optimizer. The end result was that the optimizer choosed a
ref access instead of a range access which caused errors in buildbot.

Fixed by adding more rows to the table to ensure that table scan is
more costly than range scan of the given interval.

log_t::create(): Return whether the initialisation succeeded.
It may fail if too large an innodb_log_buffer_size is specified.

copy_back(): Also copy the dummy empty ib_logfile0 so that
MariaDB Server 10.8 or later can be started after
--copy-back or --move-back.

Thanks to Daniel Black for reporting this.

This is a 10.5 version of
commit ebf36492

Table_cache_instance::operator new[](size_t): Reverted the changes
that were made in commit 8edef482
and move them to the only caller.

Use an std::atomic_flag to track thread creation in progress.
This is mainly a cleanup, the effect of this change was not measureable
in my tests.

Add threadpool functionality to restrict concurrency during "batch"
periods (where tasks are added in rapid succession).
This will throttle thread creation more agressively than usual, while
keeping performance at least on-par.

One of these cases is bufferpool load, where async read IOs are executed
without any throttling. There can be as much as 650K read IOs for
loading 10GB buffer pool.

Another one is recovery, where "fake read" IOs are executed.

Why there are more threads than we expect?
Worker threads are not be recognized as idle, until they return to the
standby list, and to return to that list, they need to acquire
mutex currently held in the submit_task(). In those cases, submit_task()
has no worker to wake, and would create threads until default concurrency
level (2*ncpus) is satisfied. Only after that throttling would happen.

The problem was that we did not handle errors properly in
JOIN::get_best_combination. In case an early error, JOIN->join_tab would
contain unintialized values, which would cause errors on cleanup().

The error in question was reported earlier, but not noticed until later.
One cause of this is that most of the sql_select.cc code just checks
thd->fatal_error and not thd->is_error().
Fixed by changing of checks of fatal_error to is_error().

This allows a user to to change the default value of MAX_SEL_ARGS (16000)
in the rare case where they neeed more generated SEL_ARGS (as part of
the range optimizer)

Raise notes if indexes cannot be used:
- in case of data type or collation mismatch (diferent error messages).
- in case if a table field was replaced to something else
  (e.g. Item_func_conv_charset) during a condition rewrite.

Added option to write warnings and notes to the slow query log for
slow queries.

New variables added/changed:

- note_verbosity, with is a set of the following options:
  basic            - All old notes
  unusable_keys    - Print warnings about keys that cannot be used
                     for select, delete or update.
  explain          - Print unusable_keys warnings for EXPLAIN querys.

The default is 'basic,explain'. This means that for old installations
the only notable new behavior is that one will get notes about
unusable keys when one does an EXPLAIN for a query. One can turn all
of all notes by either setting note_verbosity to "" or setting sql_notes=0.

- log_slow_verbosity has a new option 'warnings'. If this is set
  then warnings and notes generated are printed in the slow query log
  (up to log_slow_max_warnings times per statement).

- log_slow_max_warnings   - Max number of warnings written to
                            slow query log.

Other things:
- One can now use =ALL for any 'set' variable to set all options at once.
  For example using "note_verbosity=ALL" in a config file or
  "SET @@note_verbosity=ALL' in SQL.
- mysqldump will in the future use @@note_verbosity=""' instead of
  @sql_notes=0 to disable notes.
- Added "enum class Data_type_compatibility" and changing the return type
  of all Field::can_optimize*() methods from "bool" to this new data type.

Reviewer & Co-author: Alexander Barkov <bar@mariadb.com>
- The code that prints out the notes comes mainly from Alexander

The warning is given in case of table not found or if there is a lock
timeout. The warning is needed as in case of a lock timeout then the
persistent table stats are going to be wrong.