innobase_commit_by_xid(), innobase_rollback_by_xid(): Decrement
the reference count before freeing the transaction object to the pool.
Failure to do so might corrupt the transaction bookkeeping
if trx_create_low() returns the same object to another thread
before we are done with it.

trx_sys_close(): Detach the recovered XA PREPARE transactions from
trx_sys->rw_trx_list before freeing them.

join_tab->distinct=true means "Before doing record read with this
join_tab, call join_tab->remove_duplicates() to eliminate duplicates".
remove_duplicates() assumes that
- there is a temporary table $T with rows that are to be de-duplicated
- there is a previous join_tab (e.g. with join_tab->fields) which was
used to populate the temp.table $T.

When the query has "Impossible WHERE" and window function, then the above
conditions are not met (but we still might need a window function
computation step when the query has implicit grouping).

The fix is to not add remove_duplicates step if the select execution is
degenerate (and we'll have at most one row in the output anyway).

MDEV-14511 tried to avoid some consistency problems related to InnoDB
persistent statistics. The persistent statistics are being written by
an InnoDB internal SQL interpreter that requires the InnoDB data dictionary
cache to be locked.

Before MDEV-14511, the statistics were written during DDL in separate
transactions, which could unnecessarily reduce performance (each commit
would require a redo log flush) and break atomicity, because the statistics
would be updated separately from the dictionary transaction.

However, because it is unacceptable to hold the InnoDB data dictionary
cache locked while suspending the execution for waiting for a
transactional lock (in the mysql.innodb_index_stats or
mysql.innodb_table_stats tables) to be released, any lock conflict
was immediately be reported as "lock wait timeout".

To fix MDEV-14941, an attempt to reduce these lock conflicts by acquiring
transactional locks on the user tables in both the statistics and DDL
operations was made, but it would still not entirely prevent lock conflicts
on the mysql.innodb_index_stats and mysql.innodb_table_stats tables.

Fixing the remaining problems would require a change that is too intrusive
for a GA release series, such as MariaDB 10.2.

Thefefore, we revert the change MDEV-14511. To silence the
MDEV-13201 assertion, we use the pre-existing flag trx_t::internal.

current_select may point to data from old parser states
when calling a stored procedure with CALL

The failure happens in Item::Item when testing if we are
in having.

Fixed by explicitely reseting current_select in do_execute_sp()
and in sp_rcontext::create(). The later is also needed for
stored functions().

caused an error

The function subselect_single_select_engine::print() did not print
the WITH clause attached to a subselect with single select engine.
As a result views using suqueries with attached WITH clauses lost
these clauses when saved in frm files.

The field trx_rseg_t::trx_ref_count that was added in WL#6965 in
MySQL 5.7.5 is being incremented twice if a recovered transaction
includes both undo log partitions insert_undo and update_undo.

This reference count is being used in trx_purge(), which invokes
trx_purge_initiate_truncate() to try to truncate an undo tablespace
file. Because of the double-increment, the trx_ref_count would never
reach 0.

It is possible that after the failed truncation attempt, the undo
tablespace would be disabled for logging any new transactions until
the server is restarted (hopefully after committing or rolling back
all transactions, so that no transactions would be recovered
on the next startup).

trx_resurrect_insert(), trx_resurrect_update(): Do not increment
trx_ref_count. Instead, let the caller do that.

trx_lists_init_at_db_start(): Increment rseg->trx_ref_count only
once for each recovered transaction. Adjust comments.
Finally, if innodb_force_recovery prevents the undo log scan,
do not bother iterating the empty lists.

The problem was that max_size was acciently set to 1 in some
cases.

Other things:
- Adjust max_rows if min_rows > max_rows.
- Removed not used variable varchar_length
- Adjusted max_pack_length (safety fix)

srv_prepare_to_delete_redo_log_files(): Initialize srv_start_lsn.

1. Moving the following methods from THD to Item_change_list:
   nocheck_register_item_tree_change()
   check_and_register_item_tree_change()
   rollback_item_tree_changes()
   as they work only with the "change_list" member and don't
   require anything else from THD.
2. Deriving THD from Item_change_list

This change will help to fix "MDEV-14603 signal 11 with short stacktrace" easier.

innobase_start_or_create_for_mysql(): Only start the data dictionary
and transaction subsystems in normal server startup and during
mariabackup --export.

btr_cur_update_in_place(): Read block->index only once,
so that it cannot change to NULL after the first read.
When block->index != NULL, it must be equal to index.

btr_cur_update_in_place(): The call rw_lock_x_lock(ahi_latch) must
of course be inside the if (ahi_latch) condition. This is a mistake
that I made when backporting the fix-under-development from 10.3.

This race condition is a regression caused by MDEV-12121.

btr_cur_update_in_place(): Determine block->index!=NULL only once
in order to determine whether an adaptive hash index bucket needs
to be exclusively locked and unlocked.

If we evaluated block->index multiple times, and the adaptive hash
index was disabled before we locked the adaptive hash index, then
we would never release the adaptive hash index bucket latch, which
would eventually lead to InnoDB hanging.

innodb.truncate_inject: Replacement for innodb_zip.wl6501_error_1

Note: unlike MySQL, in some cases TRUNCATE does not return
an error in MariaDB. This should be fixed in the scope of
MDEV-13564 or similar.

Speed up compilation

Standard C++ headers contribute a lot to compilation time. Avoid algorithm
and sstream in frequently used headers.

This is a regression that was introduced in MySQL 5.7.6 in
https://github.com/mysql/mysql-server/commit/19855664de0245ff24e0753dc82723fc4e2fb7a5

fil_node_open_file(): Use proper 64-bit arithmetics for truncating
size_bytes to a multiple of a file extent size.

- Removed extra set -x -v used for debugging
- Fixed that that gcc version tests works for gcc 7

- Make Rdb_binlog_manager::unpack_value to not have a stack overrun
  when it is reading invalid data (which it currently does as we in
  MariaDB do not store binlog coordinates under BINLOG_INFO_INDEX_NUMBER,
  see comments in MDEV-14892 for details).
- We may need to store these coordinates in the future, so instead of
  removing the call of this function, let's make it work properly for
  all possible inputs.

The warning was originally added in
commit c6766305
(MySQL 4.1.12, 5.0.3) to trace claimed undo log corruption that
was analyzed in https://lists.mysql.com/mysql/176250
on November 9, 2004.

Originally, the limit was 20,000 undo log headers or transactions,
but in commit 9d6d1902
in MySQL 5.5.11 it was increased to 2,000,000.

The message can be triggered when the progress of purge is prevented
by a long-running transaction (or just an idle transaction whose
read view was started a long time ago), by running many transactions
that UPDATE or DELETE some records, then starting another transaction
with a read view, and finally by executing more than 2,000,000
transactions that UPDATE or DELETE records in InnoDB tables. Finally,
when the oldest long-running transaction is completed, purge would
run up to the next-oldest transaction, and there would still be more
than 2,000,000 transactions to purge.

Because the message can be triggered when the database is obviously
not corrupted, it should be removed. Heavy users of InnoDB should be
monitoring the "History list length" in SHOW ENGINE INNODB STATUS;
there is no need to spam the error log.