After the commit b76b69cd
loose index scan for queries with DISTINCT stopped working.
That is why that commit has to be reverted.
Additionally this patch  fixes the problem of MDEV-10880.

MDEV-15511 - Use stunnel during rsync SST if available

Use table_arg that was passed to the function, instead of dereferencing
this->table, which is a NULL pointer.

fts_query(): Remove a redundant condition (result will never be NULL),
and instead check if *result is NULL, to prevent SIGSEGV in
fts_query_free_result().

The functions fts_ast_visit() and fts_query() inside
InnoDB FULLTEXT INDEX query processing are not checking
for THD::killed (trx_is_interrupted()), like anything
that potentially takes a long time should do.

This is a port of the following change from MySQL 5.7.23,
with a completely rewritten test case.

commit c58c6f8f66ddd0357ecd0c99646aa6bf1dae49c8
Author: Aakanksha Verma <aakanksha.verma@oracle.com>
Date:   Fri May 4 15:53:13 2018 +0530

Bug #27155294 MAX_EXECUTION_TIME NOT INTERUPTED WITH FULLTEXT SEARCH USING MECAB

This is a backport of the following fix from MySQL 5.7.23.
Some code refactoring has been omitted, and the test case has
been adapted to MariaDB.

commit 7a689acaa65e9d602575f7aa53fe36a64a07460f
Author: Krzysztof Kapuścik <krzysztof.kapuscik@oracle.com>
Date:   Tue Mar 13 12:34:03 2018 +0100

Bug#27082268 Invalid FTS sync synchronization

The fix closes two issues:
Bug #27082268 - INNODB: FAILING ASSERTION: SYM_NODE->TABLE != NULL DURING FTS SYNC
Bug #27095935 - DEADLOCK BETWEEN FTS_DROP_INDEX AND FTS_OPTIMIZE_SYNC_TABLE

Both issues were related to a FTS cache sync being done during
operations that perfomed DDL actions on internal FTS tables
(ALTER TABLE, TRUNCATE). In some cases the FTS tables and/or
internal cache structures could get removed while still being
used to perform FTS synchronization leading to crashes. In other
the sync operations could not get finishes as it was waiting for
dict lock which was taken by thread waiting for the background
sync to be finished.

The changes done includes:
- Stopping background operations during ALTER TABLE and TRUNCATE.
- Removal of unused code in FTS.
- Cleanup of FTS sync related code to make it more readable and
easier to maintain.

RB#18262

We did not merge Percona XtraDB 5.6.40-84.0 yet.
The changes in it are mostly cosmetic, except for
2 bug fixes from Oracle MySQL 5.6.40, which could
be security bugs.

This was achieved by taking the applicable parts
of an earlier InnoDB commit to XtraDB:

git diff 15ec8c2f{~,} storage/innobase|
sed -e s+/innobase/+/xtradb/+|patch -p1

No commit message

Problem:
As part of bug #24938374 fix, dict_operation_lock was not taken by
fts_optimize_thread while syncing fts cache.
Due to this change, alter query is able to update SYS_TABLE rows
simultaneously. Now when fts_optimizer_thread goes open index table,
It doesn't open index table if the record corresponding to that table is
set to REC_INFO_DELETED_FLAG in SYS_TABLES and hits an assert.

Fix:
If fts sync is already in progress, Alter query would wait for sync to
complete before renaming table.

RB: #19604
Reviewed by : Jimmy.Yang@oracle.com

This is motivated by Oracle MySQL Bug #27542720 SCHEMA MISMATCH
- TABLE FLAGS DON'T MATCH, BUT FLAGS ARE NUMBERS
but using a different approach.

row_import::match_schema(): In case of a mismatch, display the
ROW_FORMAT and optionally KEY_BLOCK_SIZE of the .cfg file.

We do not accept:
1. We did not have this problem (fixed earlier and better)
 d982e717 Bug#27510150: MYSQLDUMP FAILS FOR SPECIFIC --WHERE CLAUSES
2. We do not have such options (an DBUG_ASSERT put just in case)
 bbc2e37f Bug#27759871: BACKRONYM ISSUE IS STILL IN MYSQL 5.7
3. Serg fixed it in other way in this release:
 e48d775c Bug#27980823: HEAP OVERFLOW VULNERABILITIES IN MYSQL CLIENT LIBRARY

Test case was not written correctly.

In this case we are setting the field Item_func_eq::in_eqaulity_no for the semi-join equalities.
This helps us to remove these equalites as the inner tables are not available during parent select execution
while the outer tables are not available during materialization phase.
We only have it set for the equalites for the fields involved with the IN subquery
and reset it for the equalities which do not belong to the IN subquery.

For example in case of nested IN subqueries:

    SELECT t1.a FROM t1 WHERE t1.a IN
      (SELECT t2.a FROM t2 where t2.b IN
          (select t3.b from t3 where t3.c=27 ))

there are two equalites involving the fields of the IN subquery

1) t2.b = t3.b :  the field Item_func_eq::in_eqaulity_no is set when we merge the grandchild select into the child select
2) t1.a = t2.a :  the field Item_func_eq::in_eqaulity_no is set when we merge the child select into the parent select

But when we perform case 2) we should ensure that we reset the equalities in the child's WHERE clause.

MDEV-16751: Server crashes in st_join_table::cleanup or TABLE_LIST::is_with_table_recursive_reference
            with join_cache_level>2

During muliple equality propagation for a query in which we have an IN subquery, the items in the select list of the
subquery may not be part of the multiple equality because there might be another occurence of the same field in the
where clause of the subquery.
So we keyuse_is_valid_for_access_in_chosen_plan function which expects the items in the select list of the subquery to
be same to the ones in the multiple equality (through these multiple equalities we create keyuse array).
The solution would be that we expect the same field not the same Item because when we have SEMI JOIN MATERIALIZATION SCAN,
we use copy back technique to copies back the materialised table fields to the original fields of the base tables.

This patch fixes another problem introduced by the patch for mdev-4817.
The latter changed Item_cond::fix_fields() in such a way that it could
call the virtual method is_expensive(). With the first its call
the method saves the result in Item::is_expensive_cache. For all next
calls the method returns the result from this cache. So if the item
once was determined as expensive the method always returns true.
For subqueries it's not good, because non-optimized subqueries always
is considered as expensive.
It means that the cache should be invalidated after the call of
optimize_constant_subqueries().

This patch fixes another problem introduced by the patch for mdev-4817.
The latter changed Item_cond::fix_fields() in such a way that it could
call the virtual method is_expensive(). With the first its call
the method saves the result in Item::is_expensive_cache. For all next
calls the method returns the result from this cache. So if the item
once was determined as expensive the method always returns true.
For subqueries it's not good, because non-optimized subqueries always
is considered as expensive.
It means that the cache should be invalidated after the call of
optimize_constant_subqueries().

In Galera BF (brute force) transactions may not wait for lock requests
and normally BF-transaction would select transaction holding conflicting
locks as a victim for rollback. However, background statistic calculation
transaction is InnoDB internal transaction and it has no thd i.e. it can't be
selected as a victim. If background statistics calculation transaction holds
conflicting locks to statistics tables it will cause BF lock wait long
error message. Correct way to handle background statistics calculation is to
acquire thd for transaction but that change is too big for GA-releases and
there are other reported problems on background statistics calculation.

This fix avoids adding a table to background statistics calculation if

This patch fixes another problem introduced by the patch for mdev-4817.
The latter changed Item_cond::fix_fields() in such a way that it could
call the virtual method is_expensive(). With the first its call
the method saves the result in Item::is_expensive_cache. For all next
calls the method returns the result from this cache. So if the item
once was determined as expensive the method always returns true.
For subqueries it's not good, because non-optimized subqueries always
is considered as expensive.
It means that the cache should be invalidated after the call of
optimize_constant_subqueries().