Probem was that dict_sys mutex was owned when calling function
dict_stats_save_defrag_stats() that assumes we do not own
dict_sys mutex.

Assertion `count > 0' failed in rpl_parallel_thread_pool::
get_thread, rpl.rpl_parallel failed in buildbot

The reason for this is that one thread can call
rpl_parallel_resize_pool_if_no_slaves() while
another thread calls at the same time
rpl_parallel_activate_pool(). If rpl_parallel_active_pool() is
called before rpl_parallel_resize_pool_if_no_slaves() has
finished, pool->count will be set to 0 even if there exists
active slave threads.

Added a mutex lock in rpl_parallel_activate_pool() to protect against this scenario, which seams to fix this issue.

It crashed because we accessed lex->current_select when
it was a NULL, which is the case for SP parameters or
local variables.

While the bug was reported as a regression of
MDEV-11025 Make number of page cleaner threads variable dynamic
in MariaDB Server 10.3, the code that MariaDB Server 10.2
inherited from MySQL 5.7.4 (WL#6642) looks prone to similar errors.

pc_flush_slot(): If there is no work to do, reset the is_requested
signal, to avoid potential busy-waiting in
buf_flush_page_cleaner_worker(). If the coordinator thread has shut
down, avoid resetting the is_requested event, to avoid a potential
hang at shutdown if there are multiple worker threads.

Signed-off-by: Daniel Black <daniel@linux.vnet.ibm.com>

FULLTEXT auxiliary tables

Change the logic to take mdl lock on all tables before tablespaces are
copied, rather than  lock every single tablespace just before it is
copied.

ibuf_merge_or_delete_for_page(): Invoke fil_space_acquire_silent()
instead of fil_space_acquire() in order to avoid displaying
a useless message.

We know perfectly well that a tablespace can be dropped while a
change buffer merge is pending, because change buffer merges skip
any transactional locks.

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