trx_undo_report_row_operation(): Fix a race condition that was introduced
in commit f74023b9 (MDEV-15090).
We must not access undo_block after the page latch has been released
in mtr_t::commit(), because the block could be evicted or replaced.

fil_crypt_rotate_page(): If a page is already marked as dirty,
do not move it in buf_pool.flush_list. Actual re-encryption
will happen in buf_flush_page(), and moving the page in
buf_pool.flush_list may only postpone the operation.

In the merge commit d3e4fae7
a message about innodb_force_recovery was accidentally duplicated.

- Adding socket check for MariaDB/Mysql driver

Reviewed by: serg@mariadb.com

mytop fall-back to DBD::mysql if DBD::MariaDB is not available

Apply #1546

Let us simply refuse an upgrade from earlier versions if the
upgrade procedure was not followed. This simplifies the purge,
commit, and rollback of transactions.

Before upgrading to MariaDB 10.3 or later, a clean shutdown
of the server (with innodb_fast_shutdown=1 or 0) is necessary,
to ensure that any incomplete transactions are rolled back.
The undo log format was changed in MDEV-12288. There is only
one persistent undo log for each transaction.

Builds on travis-ci.org ceased on 2021-06-15.

see also 068246c0 and 690ae1de

see also 068246c0

see also a5f6eca5

The issue was that we sent two different signals to different threads
after each other. The DEBUG_SYNC functionality cannot handle this (as
the signal is stored in a global variable) and the first one can get
lost.

Fixed by using the same signal for both threads.

When doing CREATE TABLE ... ENGINE=MyISAM SELECT ...
the MyISAM table was not completely flushed at commit
which gave some warnings about table not closed in the
atomic test suite.

Fixed by flushing the table in select_insert::prepare_eof().

- Rename DDL_IGNORE_LOG_ENTRY_CODE to DDL_LOG_IGNORE_ENTRY_CODE
  This makes it similar to all other ddl_log_entry_code's.
- Added some new comments
- ddl_log_revert() now returns != 0 if revert didn't succeed

spider tests use

--let $var= many;sql;statements
--eval $var

and this doesn't work in ps

and *never* disable tests in suite.pm based on $::opt_big_test,
this will make the test skipped both as too big (for ./mtr)
and as too small (for ./mtr --big --big).

MDEV-25867 main.trigger-trans failed in bb, Assertion `ticket->m_duration == MDL_EXPLICIT' failed in MDL_context::release_lock

release MDL on the trigger as early as possible, after everything that
cannot be done concurrently was done (under MDL), but before relocking
tables.

Not all environments have 'diff' installed. Most notably CentOS 8
does not have diff out-of-the-box. Thus users running 'cmake .' and
'make' would fail to build MariaDB, and they would think the error
was in ABI incompatibilities due to the error message emitted by CMake
when in reality simply 'diff' was missing.

This fixes it and makes the developer experience better by simply skipping
the diffing if 'diff' is not found.

## Proof

Running in a clean CentOS 8 container.

### Before

```
$ cmake .
...
-- Looking for cpuid.h
-- Looking for cpuid.h - found
-- Looking for x86intrin.h
-- Looking for x86intrin.h - found
-- Looking for event.h
-- Looking for event.h - not found
-- Configuring done
-- Generating done
-- Build files have been written to: /build

$ make
Scanning dependencies of target abi_check
CMake Error at cmake/do_abi_check.cmake:82 (MESSAGE):
  ABI check found difference between /build/include/mysql/plugin_audit.h.pp
  and /build/abi_check.out

make[2]: *** [CMakeFiles/abi_check.dir/build.make:57: CMakeFiles/abi_check] Error 1
make[1]: *** [CMakeFiles/Makefile2:168: CMakeFiles/abi_check.dir/all] Error 2
make: *** [Makefile:163: all] Error 2

$ yum install -y diffutils
...
Installed:
  diffutils-3.6-6.el8.x86_64
Complete!

$ make
[  0%] Built target abi_check
Scanning dependencies of target INFO_BIN
[  0%] Built target INFO_BIN
Scanning dependencies of target INFO_SRC
[  0%] Built target INFO_SRC
Scanning dependencies of target wsrep_api_v26
[  0%] Building C object wsrep-lib/wsrep-API/CMakeFiles/wsrep_api_v26.dir/v26/wsrep_dummy.c.o
[  0%] Building C object wsrep-lib/wsrep-API/CMakeFiles/wsrep_api_v26.dir/v26/wsrep_gtid.c.o
[  0%] Building C object wsrep-lib/wsrep-API/CMakeFiles/wsrep_api_v26.dir/v26/wsrep_loader.c.o
[  0%] Building C object wsrep-lib/wsrep-API/CMakeFiles/wsrep_api_v26.dir/v26/wsrep_uuid.c.o
[  0%] Linking C static library libwsrep_api_v26.a
[  0%] Built target wsrep_api_v26
```

### After

```
$ make
Command 'diff' not found. ABI check for /build/server/include/mysql/plugin_audit.h skipped.
Command 'diff' not found. ABI check for /build/server/include/mysql/plugin_ftparser.h skipped.
Command 'diff' not found. ABI check for /build/server/include/mysql.h skipped.
Command 'diff' not found. ABI check for /build/server/include/mysql/psi/psi_abi_v1.h skipped.
Command 'diff' not found. ABI check for /build/server/include/mysql/psi/psi_abi_v2.h skipped.
Command 'diff' not found. ABI check for /build/server/include/mysql/client_plugin.h skipped.
Command 'diff' not found. ABI check for /build/server/include/mysql/plugin_auth.h skipped.
Command 'diff' not found. ABI check for /build/server/include/mysql/plugin_password_validation.h skipped.
Command 'diff' not found. ABI check for /build/server/include/mysql/plugin_encryption.h skipped.
Command 'diff' not found. ABI check for /build/server/include/mysql/plugin_data_type.h skipped.
Command 'diff' not found. ABI check for /build/server/include/mysql/plugin_function.h skipped.
[  0%] Built target abi_check
[  0%] Built target INFO_SRC
[  0%] Built target INFO_BIN
[  0%] Built target wsrep_api_v26
[  0%] Building CXX object wsrep-lib/src/CMakeFiles/wsrep-lib.dir/server_state.cpp.o
```

If diff is installed, those warnings are simply not shown. Builds pass
without the need to install 'diff'.

Do not execute user callback just after pwrite. Instead, submit user
function as task into thread pool. This way, the IO thread would not hog
aiocb, which is a limited (in Innodb) resource

This test failed in case it was run in PS mode and for embedded server

The reason of test failure was that the following fields
  affected_row, server_status, insert_id
of the structure MYSQL_STMT weren't update on calling
mysql_stmt_next_result() in case combination of binary protocol
and embedded server used.

fixes a bunch of tests failures in --ps --embed

also, don't use cli_advanced_command().

do not try to detect metadata change (and reprepare) for
internal short-lived TABLE_LIST objects that couldn't have
possibly lived long enough to see prepare and cache the metadata.

 ' Access denied; you need (at least one of) the SUPER privilege(s) for this operation
on executing SET system_variable=.... in PS mode