make live checksum to be returned in handler::info(),
and slow table-scan checksum to be calculated in handler::checksum().

part of
MDEV-16249 CHECKSUM TABLE for a spider table is not parallel and saves all data in memory in the spider head by default

Do not consider rows of Information_schema.files where
LOGFILE_GROUP_NAME is NULL.

In wsrep_plugins_post_init we iterate all theads and if they are
galera appliers (wsrep_applier) we init session variables. However,
current_thd was not set and recent changes on session variables
require holding LOCK_gloal_system_variables mutex.

Regression after reverting fair THD members constructors/destructors.
vars_list can be used standalone, in such cases destructor is needed.

Part of MDEV-14984 - regression in connect performance

The accessor dtuple_get_nth_v_field() was defined differently between
debug and release builds in MySQL 5.7.8 in
mysql/mysql-server@c47e1751b742454de553937039bbf2bcbe3c6bc7
and a debug assertion to document or enforce the questionable assumption
tuple->v_fields == &tuple->fields[tuple->n_fields] was missing.

This was apparently no problem until MDEV-11369 introduced instant
ADD COLUMN to MariaDB Server 10.3. With that work present, in one
test case, trx_undo_report_insert_virtual() could in release builds
fetch the wrong value for a virtual column.

We replace many of the dtuple_t accessors with const-preserving
inline functions, and fix missing or misleadingly applied const
qualifiers accordingly.

log_checkpoint(), log_make_checkpoint_at(): Remove the parameter
write_always. It seems that the primary purpose of this parameter
was to ensure in the function recv_reset_logs() that both checkpoint
header pages will be overwritten, when the function is called from
the never-enabled function recv_recovery_from_archive_start().

create_log_files(): Merge recv_reset_logs() to its only caller.

Debug instrumentation: Prefer to flush the redo log, instead of
triggering a redo log checkpoint.

page_header_set_field(): Disable a debug assertion that will
always fail due to MDEV-19344, now that we no longer initiate
a redo log checkpoint before an injected crash.

In recv_reset_logs() there used to be two calls to
log_make_checkpoint_at(). The apparent purpose of this was
to ensure that both InnoDB redo log checkpoint header pages
will be initialized or overwritten.
The second call was removed (without any explanation) in MySQL 5.6.3:
mysql/mysql-server@4ca37968da54ddc6b3b6628f41428ddba1c79bb8

In MySQL 5.6.8 WL#6494, starting with
mysql/mysql-server@00a0ba8ad92569fcf08212b3b8cf046dc8a0ce10
the function recv_reset_logs() was not only invoked during
InnoDB data file initialization, but also during a regular
startup when the redo log is being resized.

mysql/mysql-server@45e91679832219e2593c77185342f11f85232b58
in MySQL 5.7.2 removed the UNIV_LOG_ARCHIVE code, but still
did not remove the parameter write_always.

Disable (hopefully temprorary) this check. Also add tests for some serialized
functions.

Originally introduced by e972125f to avoid harmless wait for
LOCK_global_system_variables in a newly created thread, which creation was
initiated by system variable update.

At the same time it opens dangerous hole, when system variable update
thread already released LOCK_global_system_variables and ack_receiver
thread haven't yet completed new THD construction. In this case THD
constructor goes completely unprotected.

Since ack_receiver.stop() waits for the thread to go down, we have to
temporarily release LOCK_global_system_variables so that it doesn't
deadlock with ack_receiver.run(). Unfortunately it breaks atomicity
of rpl_semi_sync_master_enabled updates and makes them not serialized.

LOCK_rpl_semi_sync_master_enabled was introduced to workaround the above.
TODO: move ack_receiver start/stop into repl_semisync_master
enable_master/disable_master under LOCK_binlog protection?

Part of MDEV-14984 - regression in connect performance

Only take LOCK_plugin for plugin system variables.

Reverted optimisation that was originally done for session tracker: it
makes much less sense now. Specifically only if connections would want to
track plugin session variables changes and these changes would actually
happen frequently. If this ever becomes an issue, there're much better
ways to optimise this workload.

Part of MDEV-14984 - regression in connect performance

Rather than parsing session_track_system_variables when thread starts, do
it when first trackable event occurs.

Benchmarked on a 2socket/20core/40threads Broadwell system using sysbench
connect brencmark @40 threads (with select 1 disabled):
101379.77 -> 143016.68 CPS, whereas 10.2 is currently at 137766.31 CPS.

Part of MDEV-14984 - regression in connect performance

When enabling system variables tracker, make a copy of
global_system_variables.session_track_system_variables
under LOCK_global_system_variables. This protects from concurrent variable
updates and potential freed memory access, as well as from variable
reconstruction (which was previously protected by LOCK_plugin).

We can also use this copy as a session variable pointer, so that we don't
have to allocate memory and reconstruct it every time it is referenced.

For this very reason we don't need buffer_length stuff anymore.

As well as don't we need to take LOCK_plugin early in ::enable().
Unified ::parse_var_list() to acquire LOCK_plugin unconditionally.
For no apparent reason it wasn't previously acquired for global
variable update.

Part of MDEV-14984 - regression in connect performance

One less new/delete per connection.

Removed m_mem_flag since most allocs are thread specific. The only
exception are allocs performed during initialization.

Removed State_tracker and Session_tracker constructors as they don't make
sense anymore.

No reason to access session_sysvars_tracker via get_tracker(), so access
it directly instead.

Part of MDEV-14984 - regression in connect performance

One less new/delete per connection.

Part of MDEV-14984 - regression in connect performance

Saves 2 new/delete per connection.

Part of MDEV-14984 - regression in connect performance

tool_list is a temporary list needed only for SET SESSION
session_track_system_variables, so allocate it on stack instead.

Sane reinit() calls.

Saves 2 new/delete per connection.

Part of MDEV-14984 - regression in connect performance

One less new/delete per connection.

Part of MDEV-14984 - regression in connect performance

- Session_sysvars_tracker::server_init_check() -> sysvartrack_validate_value()
- Session_sysvars_tracker::check_var_list()    -> sysvartrack_validate_value()

- Session_sysvars_tracker::server_init_process() -> sysvartrack_global_update()
- sysvartrack_reprint_value()                    -> sysvartrack_global_update()

- sysvartrack_value_len()       -> sysvartrack_session_value_ptr()
- sysvartrack_value_construct() -> sysvartrack_session_value_ptr()

- sysvartrack_update() -> Session_sysvars_tracker::update()
- Session_tracker::server_boot_verify() -> session_tracker_init()
- sysvar_tracker() -> /dev/null

Part of MDEV-14984 - regression in connect performance

- m_enabled is initialised by the base class constructor
- removed unused schema_track_inited
- moved Transaction_state_tracker constructor to declaration
- common enable()
- removed unused Session_sysvars_tracker::check_str()
- classes are "private" by default
- don't even try to compile for embedded

Part of MDEV-14984 - regression in connect performance

- return proper type
- removed useless node argument
- removed useless mem_flag
- classes are "private" by default
- simplified iterators

Part of MDEV-14984 - regression in connect performance

Note: preserved original behaviour, where remaining trackers are not reset
on error from store(). This effectively means subsequent statements will
start tracking from unclean state.

Part of MDEV-14984 - regression in connect performance

Adjusted the Item_func_group_concat::print function to take into account
limit if present with GROUP_CONCAT

on tablespace files

Fix is to always add Full Control for NetworkService account, for every
file that copyback/moveback copies around.

If required privilege is missing, dump the output from "SHOW GRANTS"
into mariabackup log.

This will help troubleshooting, and make the bug reproducible.

The statement

SET GLOBAL innodb_encryption_rotate_key_age=0;

would have the unwanted side effect that ENCRYPTION=DEFAULT tablespaces
would no longer be encrypted or decrypted according to the setting of
innodb_encrypt_tables.

We implement a trigger, so that whenever one of the following is executed:

SET GLOBAL innodb_encrypt_tables=OFF;
SET GLOBAL innodb_encrypt_tables=ON;
SET GLOBAL innodb_encrypt_tables=FORCE;

all wrong-state ENCRYPTION=DEFAULT tablespaces will be added to
fil_system_t::rotation_list, so that the encryption will be added
or removed.

Note: This will *NOT* happen automatically after a server restart.
Before reading the first page of a data file, InnoDB cannot know
the encryption status of the data file. The statement
SET GLOBAL innodb_encrypt_tables will have the side effect that
all not-yet-read InnoDB data files will be accessed in order to
determine the encryption status.

innodb_encrypt_tables_validate(): Stop disallowing
SET GLOBAL innodb_encrypt_tables when innodb_encryption_rotate_key_age=0.
This reverts part of commit 50eb40a2
that addressed MDEV-11738 and MDEV-11581.

fil_system_t::read_page0(): Trigger a call to fil_node_t::read_page0().
Refactored from fil_space_get_space().

fil_crypt_rotation_list_fill(): If innodb_encryption_rotate_key_age=0,
initialize fil_system->rotation_list. This is invoked both on
SET GLOBAL innodb_encrypt_tables and
on SET GLOBAL innodb_encryption_rotate_key_age=0.

fil_space_set_crypt_data(): Remove.

fil_parse_write_crypt_data(): Simplify the logic.

This is joint work with Marko Mäkelä.

Closes #1044

MDEV-17654 Incorrect syntax returned for column with CHECK constraint in the "SHOW CREATE TABLE ..." result

Prepend COMMENT before CHECK constraint in SHOW CREATE

Closes #924

The working directory, resource limits and core pattern will
aid the user finding a core file in the case of failure.

While the core file size is most relevant however other resource
limits may give a clue as the the cause of the fatal signal so
include them also.

As signal handler functions are limited, proc filesystem reads/
readlink calls are used instead of the more obvious getcwd/getrlimits
functions which aren't listed as signal safe.

Results in output of the form:

Writing a core file: working directory at /tmp/datadir
Resource Limits:
Limit                     Soft Limit           Hard Limit Units
Max cpu time              unlimited            unlimited seconds
Max file size             unlimited            unlimited bytes
Max data size             unlimited            unlimited bytes
Max stack size            8388608              unlimited bytes
Max core file size        unlimited            unlimited bytes
Max resident set          unlimited            unlimited bytes
Max processes             47194                47194 processes
Max open files            1024                 4096 files
Max locked memory         65536                65536 bytes
Max address space         unlimited            unlimited bytes
Max file locks            unlimited            unlimited locks
Max pending signals       47194                47194 signals
Max msgqueue size         819200               819200 bytes
Max nice priority         0                    0
Max realtime priority     0                    0
Max realtime timeout      unlimited            unlimited            us
Core pattern: |/usr/libexec/abrt-hook-ccpp %s %c %p %u %g %t %P %I

Segmentation fault (core dumped)

Closes #537

use s->fields instead of s->stored_fields. extra_null_bitmap is allocated in Table_triggers_list::prepare_record_accessors with respect to virtual fields, so it will not overflow

Closes #1292

If a derived table has SELECT DISTINCT, provide index statistics for it so that the join optimizer in the
upper select knows that ref access to the table will produce one row.

This reverts commit 61f370a3
and implements a simpler fix that is straightforward to merge to 10.3.

lock_print_info: Renamed from PrintNotStarted. Dump the
entire contents of trx_sys->mysql_trx_list.

lock_print_info_rw_recovered: Like lock_print_info, but dump
only recovered transactions in trx_sys->rw_trx_list.

lock_print_info_all_transactions(): Dump both trx_sys->mysql_trx_list
and trx_sys->rw_trx_list.

TrxLockIterator, TrxListIterator, lock_rec_fetch_page(): Remove.
This is a partial backport of the 10.3
commit a447980f
which removed the race-condition-prone ability of the InnoDB monitor
to read relevant pages into the buffer pool for some record locks.

In InnoDB error messages, replace the hyperlink URLs to point
to the MariaDB knowledge base.