Forced columns of recursive CTEs to be nullable. SQL standard
requires this only from recursive columns, but in our code
so far we do not differentiate between recursive and non-recursive
columns when aggregating types of the union that specifies a
recursive CTE.

Problem was that we used table->s->db_type() for accessing
handlerton of opened file instead of table->file->ht

Other bug fixed:
- Ensure that we set error if reopen_tables() fails
  (This was the cause of assert)

The predicate dict_table_is_discarded() checks whether
ALTER TABLE…DISCARD TABLESPACE has been executed.

Replace most occurrences of dict_table_is_discarded() with
checks of dict_table_t::space. A few checks for the flag
DICT_TF2_DISCARDED are necessary; write them inline.

Because !is_readable() implies !space, some checks for
dict_table_is_discarded() were redundant.

Fixed by using exactly the same filtering conditions as specified by standard
in 7.6 <table reference> General Rules

MDEV-14823 Wrong error message upon selecting from a system_time partition
MDEV-15956 Strange ER_UNSUPPORTED_ACTION_ON_GENERATED_COLUMN upon ALTER on versioning column

MDEV-16043 Assertion thd->Item_change_list::is_empty() failed in mysql_parse upon SELECT from a view reading from a versioned table

Lost restore_active_arena().
Using of Query_arena_stmt is suggested instead.

Store transaction start time in thd->transaction.start_time.
THD::transaction_time() wraps over transaction.start_time taking into
account current status of BEGIN.

Don't use hidden system time in versioning,
but keep the system time logic in THD
to workaround low-res system clock and
replication not versioned to versioned.

This reverts MDEV-14788 (System versioning cannot
be based on local timestamps, as it is now).
Versioning is based on local timestamps again,
but timestamps are protected by MDEV-15923
(option to control who can set session @@timestamp).

--secure-timestamp=NO|SUPER|REPLICATION|YES

remove the redundant declaration tail

this is always enabled now,
no need for a conditional

rename LString/XString classes, remove unused ones

Make sure that SELECT_LEX_UNIT::derived, behaves as documented
(points to the "TABLE_LIST representing this union in the
embedding select"). For recursive CTE this was not necessarily
the case, it could've pointed to the TABLE_LIST inside the CTE,
not in the embedding select.

To fix:
* don't update unit->derived in mysql_derived_prepare(), pass derived
  as an argument to st_select_lex_unit::prepare()
* prefer to set unit->derived in TABLE_LIST::init_derived()
  to the TABLE_LIST in the embedding select, not to the recursive
  reference. Fail if there are many TABLE_LISTs in the embedding
  select with conflicting FOR SYSTEM_TIME clauses.

cleanup:
* remove redundant THD* argument from st_select_lex_unit::prepare()

it's internal storage engine error, don't let it leak
into the upper layer.

Make --gdb to take an optional argument *only* if it's
written after '=', not after a space.

followup for 339b9055

In InnoDB, CREATE TEMPORARY TABLE does not allow FULLTEXT INDEX.
Replace a condition with a debug assertion, and add a test.

Problem:

Fix for Bug #21348684 (#Rb9581) introduced a conditional debug execute
'buf_pool_resize_chunk_null', which causes new chunks memory for 2nd
buffer pool instance is freed.

Buffer pool resize function removes all old chunks entry from
'buf_chunk_map_reg' and add new chunks entry into it. But when
'buf_pool_resize_chunk_null' is set true, 2nd buffer pool
instance's chunk entries are not added into 'buf_chunk_map_reg'.
When purge thread tries to access that buffer chunk, it leads to
debug assertion.

Fix:

Added old chunk entries into 'buf_chunk_map_reg' for 2nd buffer pool
instance when 'buf_pool_resize_chunk_null' debug condition is set to true.

Reviewed by: Jimmy <Jimmy.Yang@oracle.com>
RB: 18664

PROBLEM

Issue found during ntest run is a regression of  Bug #27141613. The
issue is basically when index is being freed due to an error during its
creation,when the index isn't added to dictionary cache its field
columns are not set, the derefrencing of null col pointer during the
clean of index from the virtual column's leads to a crash.

NOTE: Also test i_innodb.virtual_debug was failing on 32k page size and
above for the newly added scenario. Fixed that.

FIX

Added a check that if only the index is cached , the virtual index
freeing from the virtual cols index list is performed.

Reviewed by: Satya Bodapati<satya.bodapati@oracle.com>
RB: 18670

PROBLEM
=======
When add of virtual index fails with DB_TOO_BIG_RECORD , the virtual
index being freed isn't removed from the list of indexes a virtual
column(which is part of the index). This while the undo log is read
could fetch a wrong value during rollback and cause the assertion
reported in the bug particularly.

FIX
===
Added a function that is called when the virtual index being freed would
allow the index be removed from the index list of virtual column which
was a field of that index.

Reviwed By: Jimmy Yang<Jimmy.Yang@oracle.com>
RB: 18528

PROBLEM
-------

Whenever an fts table is created it registers itself in a queue which
is operated by a background thread whose job is to optimize the
fts tables in background. Additionally we place these fts tables in
non-LRU list so that they cannot be evicted from cache. But in the
scenario when a node is brought up which is already having fts
tables ,we first try to load the fts tables in dictionary ,but we skip
the part where it is added in background queue and in non-LRU list because
the background thread is not yet created,so these tables are loaded
but they can be evicted from the cache. Now coming to the deadlock scenario

1. A Server background thread is trying to evict a table from the cache
    because the cache is full,so it scans the LRU list for the tables it can
    evict.It finds the fts table (because of the reason explained above)
    can be evicted and it takes the dict_sys->mutex (this is a system wide mutex)
    submits a request to  the background thread to remove this table from queue
    and waits it to be completed.

2.  In the mean time fts_optimize_thread() is processing another job
    in the queue and needs dict_sys->mutex for a small amount of time,
    but it cannot get it because it is blocked by the first background thread.

So Thread 1 is waiting for its job to be completed by Thread 2,whereas Thread 2
is waiting for dict_sys->mutex held by thread 1 ,causing the deadlock.

FIX

Problem:

when incorrect value is assigned to innodb_data_file_path or
innodb_temp_data_file_path parameter, Innodb returns error and logs error
message in mysqlds.err file but there is no information in error message about
the parameter which causes Innodb initialization is failed.

Fix:

Added error message with parameter name and value, which causes Innodb
initialization is failed.

Reviewed by: Jimmy <Jimmy.Yang@oracle.com>
RB: 18206

Compressed blob columns didn't accept data at their capacity. E.g. storing
255 bytes to TINYBLOB results in "Data too long" error.

Now it is allowed assuming compression method was able to produce shorter
string (so that both metadata and compressed data fits blob) and
column_compression_threshold is lower than blob.

If no compression was performed, we still have to reserve additional byte
for metadata and thus we perform normal data truncation and return it's
status.