prevent potential stalls for when all slots are used up, and all io threads
are used up, and io callbacks are slow.

Removing redundant space character after the data type comment
in SHOW CREATE TABLE, so the output changes from e.g.:

  a TIME /* mariadb-5.3 */  DEFAULT NULL

to

  a TIME /* mariadb-5.3 */ DEFAULT NULL

This is a prerequisite for MDEV-19906.

- Making classes Field_time, Field_datetime, Field_timestamp abstract
- Adding instantiable Field_time0, Field_datetime0, Field_timestamp0 classes
- Removing redundant cast in field_conv.cc, item_timefunc.cc, sp.cc in calls for set_time() and get_timestamp()
- Replacing store_TIME() to store_timestamp() in log.cc and removing redundant cast

With MDEV-16678, some InnoDB background tasks will acquire MDL,
and we must filter out such requests in the test.
For this test, an alternative might have been to use wait_all_purged.inc.

1. Fix places where data race warnings were relevant.

tls_worker_data::m_state should be modified under mutex protection,
since both maintainence timer and current worker set this flag.

2. Suppress warnings that are legitimate, yet harmless.
Apparently, the dirty reads in waitable_task::get_ref_count() or
write_slots->pending_io_count()

Avoiding race entirely without side-effects here is tricky,
and the effects of race is harmless.

The worst thing that can happen due to race is an extra wait notification,
under rare circumstances.

srv_purge_wakeup() is called under protection of latch in
purge_sys_t::resume()

move sync check code before acquiring that latch.

Now that FIL_TYPE_LOG no longer exists, let us remove some redundant
comparisons of fil_space_t::purpose.

fil_flush_low(): Do not distinguish FIL_TYPE_TEMPORARY.

fil_space_get_space(): Assume that space->purpose is valid.

The merge commit 68fe5f53 missed this.

page_set_autoinc(): Check if any change would take place,
and omit the mtr_t::OPT parameter. This should avoid
unnecessarily redo log writes for ROW_FORMAT=COMPRESSED pages.

The merge a8ed0f77
was accidentally a null-merge.

MDEV-18046: Assortment of crashes, assertion failures and ASAN errors in mysql_show_binlog_events

MDEV-18046: Assortment of crashes, assertion failures and ASAN errors in mysql_show_binlog_events

Problem:
========
SHOW BINLOG EVENTS FROM <pos> reports following assert when ASAN is enabled.

uint32 binlog_get_uncompress_len(const char*):
  Assertion `(buf[0] & 0xe0) == 0x80' failed

Fix:
===
**Part11: Converted debug assert to error handler code**

Problem:
========
SHOW BINLOG EVENTS FROM <pos> reports following ASAN error.

AddressSanitizer: heap-buffer-overflow on address
READ of size 1 at 0x60e00009cf71 thread T28
#0 0x55e37e034ae2 in net_field_length

Fix:
===
**Part10: Avoid reading out of buffer**

Problem:
========
SHOW BINLOG EVENTS FROM <pos> reports following assert when ASAN is enabled.

Query_log_event::Query_log_event(const char*, uint,
    const Format_description_log_event*, Log_event_type):
  Assertion `(pos) + (6) <= (end)' failed

Fix:
===
**Part9: Removed additional DBUG_ASSERT**

Problem:
========
SHOW BINLOG EVENTS FROM <pos> reports following ASAN error

AddressSanitizer: SEGV on unknown address
The signal is caused by a READ memory access.
User_var_log_event::User_var_log_event(char const*, unsigned int,
    Format_description_log_event const*)

Implemented part of upstream patch.
commit: mysql/mysql-server@a3a497ccf7ecacc900551fb1e47ea4078b45c351

Fix:
===
**Part8: added checks to avoid reading out of buffer limits**

Problem:
========
SHOW BINLOG EVENTS FROM <pos> reports following ASAN error
"heap-buffer-overflow on address" and some times it asserts.

Table_map_log_event::Table_map_log_event(const char*, uint,
    const Format_description_log_event*)
Assertion `m_field_metadata_size <= (m_colcnt * 2)' failed.

Fix:
===
**Part7: Avoid reading out of buffer**


Converted debug assert to error handler code.

Problem:
========
SHOW BINLOG EVENTS FROM <pos> reports following ASAN error

AddressSanitizer: heap-buffer-overflow on address 0x60400002acb8
Load_log_event::copy_log_event(char const*, unsigned long, int,
    Format_description_log_event const*)

Fix:
===
**Part6: Moved the event_len validation to the begin of copy_log_event function**

Problem:
========
SHOW BINLOG EVENTS FROM <pos> reports following ASAN error

AddressSanitizer: heap-buffer-overflow on address
String::append(char const*, unsigned int)
Query_log_event::pack_info(Protocol*)

Fix:
===
**Part5: Added check to catch buffer overflow**

Problem:
========
SHOW BINLOG EVENTS FROM <pos> reports following ASAN error

heap-buffer-overflow within "my_strndup" in Rotate_log_event

my_strndup /mysys/my_malloc.c:254
Rotate_log_event::Rotate_log_event(char const*, unsigned int,
    Format_description_log_event const*)

Fix:
===
**Part4: Improved the check for event_len validation**

Problem:
========
SHOW BINLOG EVENTS FROM <pos> reports following crash when ASAN is enabled.

SEGV on unknown address
in inline_mysql_mutex_destroy
in my_bitmap_free
in Update_rows_log_event::~Update_rows_log_event()

Fix:
===
**Part3: Initialize m_cols_ai.bitmap to NULL**

Problem:
========
SHOW BINLOG EVENTS FROM <pos> reports following assert when ASAN is enabled.

Rows_log_event::Rows_log_event(const char*, uint,
    const Format_description_log_event*):
Assertion `var_header_len >= 2'

Implemented part of upstream patch.
commit: mysql/mysql-server@a3a497ccf7ecacc900551fb1e47ea4078b45c351

Fix:
===
**Part2: Avoid reading out of buffer limits**

Problem:
========
SHOW BINLOG EVENTS FROM <pos> causes a variety of failures, some of which are
listed below. It is not a race condition issue, but there is some
non-determinism in it.

Analysis:
========
"show binlog events from <pos>" code considers the user given position as a
valid event start position. The code starts reading data from this event start
position onwards and tries to map it to a set of known events. Each event has
a specific event structure and asserts have been added to ensure that read
event data satisfies the event specific requirements. When a random position
is supplied to "show binlog events command" the event structure specific
checks will fail and they result in assert.

Fix:
====
The fix is split into different parts. Each part addresses either an ASAN
issue or an assert/crash.

**Part1: Checksum based position validation when checksum is enabled**


Using checksum validate the very first event read at the user specified
position. If there is a checksum mismatch report an appropriate error for the
invalid event.

INNOBASE_ALTER_NOVALIDATE: Remove the set of operations
INNOBASE_ONLINE_CREATE that was accidentally included in the
definition.

In the merge of 82187a12 to 10.3
(in commit eda71979) the flags
were defined correctly.

This bug was caught by the test innodb_zip.index_large_prefix.

The test encryption.innodb-redo-badkey will by design cause access
to pages that appear corrupted (due to incorrect encryption key).
Let us disable the page dumps by requiring the test to be run on
a debug server. Page dumps on debug builds were already disabled
in MDEV-19766.

- For partition table, tbl_name_len is calculated wrongly. So it leads to
this uninitialised value warnings