remove dead code

Merge pull request #667

srv_purge_should_exit(): Remove the parameter n_purged.
If we happened to have n_purged==0 while some transaction was still
active, and then that transaction was added to the history list,
we were prematurely stopping the purge. It is more appropriate to
first check for trx_sys.any_active_transactions() == 0
(this count can only decrease during shutdown) and then for
trx_sys.history_size() == 0 (that count typically decreases, but
can increase when any remaining active transactions are committed
or rolled back).

innodb.dml_purge: Remove a server restart, and explicitly wait for
purge, and use FLUSH TABLE FOR EXPORT to read the file contents.
This will make the test run faster, easier to debug, and also
allow it to run with --embedded. This might also help repeat
MDEV-11802 better. The issue MDEV-13603 remains will remain tested
by innodb.table_flags.

purge_sys_t::n_submitted: Document that it is only accessed by
srv_purge_coordinator_thread.

purge_sys_t::n_completed: Exclusively use my_atomic access.

srv_task_execute(): Simplify the code.

srv_purge_coordinator_thread(): Test the cheaper condition first.

trx_purge(): Atomically access purge_sys.n_completed.
Remove some code duplication.

trx_purge_wait_for_workers_to_complete(): Atomically access
purge_sys.n_completed. Remove an unnecessary local variable.

trx_purge_stop(): Remove a redundant assignment.

row_ins_sec_index_entry(): Compare a pointer to fil_system.sys_space,
not to a numeric constant. This code was recently changed in MDEV-13637,
and the condition was essentially disabled, potentially causing the
change buffer to grow uncontrollably when something is inserted into
a table that has secondary indexes and resides in the system tablespace.

Thanks to Daniel Black for pointing out that clang 7 flagged a warning
for the comparison of a pointer to an integer.

row_import_for_mysql(): Fix a possible compiler warning.

There is no need for MariaDB Backup to be versioned. Other packages are
very unlikely to need to depend on a certain generation of this package.

Also for MariaDB Backup to run, it does not need the server, but client,
and from client only core parts.

dict_sys_tables_type_valid(): Do not reject NO_ROLLBACK (sequence)
in ROW_FORMAT=REDUNDANT.

dict_load_table_low(): When flagging an error, assign *table = NULL.
Failure to do so could cause a crash if an error was flagged when
accessing INFORMATION_SCHEMA.INNODB_SYS_TABLES.

make its lifetime as short as possible

for historical row ROW_COPY_DATA -> ROW_COPY_POINTER for lower memory
consumption and better performance

MDEV-15742 Assertion `table_share->tmp_table != NO_TMP_TABLE ||
m_lock_type == 1' failed in handler::ha_write_row

Renaming methods:
- Field::make_field(Send_field*) to make_send_field(..)
- Item::make_field(THD *,Send_field *) to make_send_field(..)
- Item::init_make_field(Send_field *, enum_field_type) to init_make_send_field(..)

These names looked similar to other functions that are used
for a very different purpose (creating Field instances):
- Public function "Field * make_field(..)"
- Method "Field *Column_defitinion::make_field(..)"

The rename makes it's easier to search the code using "grep".

MDEV-14762 Server crashes in MDL_ticket::has_stronger_or_equal_type upon inserting into temporary sequence

Fix is to not upgrade MDL locks for temporary tables

Found via `codespell -i 3 -w --skip="./debian/po" -I ../mariadb-server-word-whitelist.txt  ./cmake/ ./debian/ ./Docs/ ./include/ ./man/ ./plugin/ ./strings/`

Problem was the Item_field::Item_field(THD*, Field*) had old code
that put a null pointer in orig_field_names. Now, when we have
proper re-prepare if table definition changes, this is not needed
anymore.

It will only build if there is network access, which is a strict no-go
for Linux distributions. Thus the AWS plugin needs to be a custom built
only special plugin that is not built as part of the normal sources.

This fixes the build error in e.g. Launchpad:

  Performing download step (git clone) for 'aws_sdk_cpp'
  cd "/<<PKGBUILDDIR>>/builddir/plugin/aws_key_management" && /usr/bin/cmake ..
  Cloning into 'aws-sdk-cpp'...
  fatal: unable to access 'https://github.com/awslabs/aws-sdk-cpp.git/':
  Could not resolve host: github.com

RocksDB configure step checks that platform is 64-bit and little endian,
so limit the .deb packages to be built only on those platforms.

List of official Debian platforms at
https://www.debian.org/ports/index.en.html

A non-MariaDB.org contributor introduced the epoch 1: in Debian.
There is no way to revert it, so we just need to adapt to it to
ensure no 10.3 installation would downgrade to that version in
Debian/Ubuntu, as 1: is considered higher than any version before.

The crash occurs when a thread that is closing its connection attempts to
access Spider transaction information when another thread has freed that memory
while processing Spider plugin deinit.  This occurs because Spider does not
adjust the plugin's reference count when it sets a transaction information
pointer for the plugin.

The fix I implemented changes the way Spider sets the transaction information
pointer to use thd_set_ha_data() so that Spider's plugin reference counter is
adjusted as well.

Author:
  Jacob Mathew.

Reviewer:
  Kentoku Shiba.

Merged From:
  bb-10.3-MDEV-7914

Increasing the length of MESSAGE_TEXT from 128 to MYSQL_ERRMSG_SIZE which is the max length of the
error message

Use trx_sys_t::trx_list instead.

Replaced "list of transactions created for MySQL" with "list of all
transactions". This simplifies code and allows further removal of
trx_sys.m_views.

trx_free_resurrected(): Remove, unused function

The test innodb.101_compatibility occasionally fails, because the flags
for the tables tdd and tp are not always converted back. Thus, the
second attempt of corrupting the flags will update garbage to garbage,
and cause test failure.

This started failing related to one or two MDEV-12266 commits affecting
the function fsp_flags_try_adjust().

fsp_flags_try_adjust(): If the file has not been opened (space->size==0),
try determining its size by reading the file. Only if the file is not
readable, give up.

Also, avoid dummy writes in the Perl script, and add some instrumentation.

The crash occurs when a thread that is closing its connection attempts to
access Spider transaction information when another thread has freed that memory
while processing Spider plugin deinit.  This occurs because Spider does not
adjust the plugin's reference count when it sets a transaction information
pointer for the plugin.

The fix I implemented changes the way Spider sets the transaction information
pointer to use thd_set_ha_data() so that Spider's plugin reference counter is
adjusted as well.

Author:
  Jacob Mathew.

Reviewer:
  Kentoku Shiba.

- Adding "return true" into LEX::set_system_variable()
  and LEX::set_default_system_variable() after my_error().
  This makes the parser exit on error immediately.
  Previously, the error was caught only in mysql_parser(),
  a few lines after the parse_sql() call.
- Fixing "--error 1272" to "--error ER_VARIABLE_IS_NOT_STRUCT" in tests

log_write_up_to(): Erase the end of the current log block.
Simplify the computation of pad_size.

log_buffer_switch(): Evaluate a condition only once.

- recovered_lsn shouldn't be initialized during xtrabackup_copy_logfile().
If partial redo log read during the end of xtrabackup_copy_logfile() then
recovered_lsn will be different from scanned_lsn. Re-initialization of
recovered_lsn could lead to partial read again. It is a regression of
MDEV-14545