- Set index columns to be read when using index_merge, even if TABLE->no_keyread is 
  set for the table (happens for multi-table UPDATEs)

The constructor for Query_log_event allocated 2 bytes too few for
extra space needed by Query cache. (Not sure if this is reproducible
in practice, as there are often a couple of extra bytes allocated
for unused string zero terminators, but better safe than sorry).

Analysis:

When a subquery that needs a temp table is executed during
the prepare or optimize phase of the outer query, at the end
of the subquery execution all the JOIN_TABs of the subquery
are replaced by a new JOIN_TAB that selects from the temp table.
However that temp table has no corresponding TABLE_LIST.
Once EXPLAIN execution reaches its last phase, it tries to print
the names of the subquery tables through its TABLE_LISTs, but in
the case of this bug there is no such TABLE_LIST (it is NULL),
hence a crash.

Solution:
The fix is to block subquery evaluation inside
Item_func_like::fix_fields and Item_func_like::select_optimize()
using the Item::is_expensive() test.

        Optimizator fails using index with ST_Within(g, constant_poly).

per-file comments:
  mysql-test/r/gis-rt-precise.result
        test result fixed.
  mysql-test/r/gis-rtree.result
        test result fixed.
  mysql-test/suite/maria/r/maria-gis-rtree-dynamic.result
        test result fixed.
  mysql-test/suite/maria/r/maria-gis-rtree-trans.result
        test result fixed.
  mysql-test/suite/maria/r/maria-gis-rtree.result
        test result fixed.
  storage/maria/ma_rt_index.c
        Use MBR_INTERSECT mode when optimizing the select WITH ST_Within.
  storage/myisam/rt_index.c
        Use MBR_INTERSECT mode when optimizing the select WITH ST_Within.

could lead an to exponential growth of the imerge lists.

- In JOIN::exec(), make the having->update_used_tables() call before we've
  made the JOIN::cleanup(full=true) call. The latter frees SJ-Materialization
  structures, which correlated subquery predicate items attempt to walk afterwards.

- Correct testcases.

- Disable IndexConditionPushdown for reverse scans.

  
  Analysis:
  The optimizer detects an empty result through constant table optimization.
  Then it calls return_zero_rows(), which in turns calls inderctly
  Item_maxmin_subselect::no_rows_in_result(). The latter method set "value=0",
  however "value" is pointer to Item_cache, and not just an integer value.
  
  All of the Item_[maxmin | singlerow]_subselect::val_XXX methods does:
    if (forced_const)
      return value->val_real();
  which of course crashes when value is a NULL pointer.
  
  Solution:
  When the optimizer discovers an empty result set, set
  Item_singlerow_subselect::value to a FALSE constant Item instead of NULL.

    Handle the 'set read_only=1' in lighter way, than the FLUSH TABLES READ LOCK;
    For the transactional engines we don't wait for operations on that tables to finish.

per-file comments:
 mysql-test/r/read_only_innodb.result
MDEV-136 Non-blocking "set read_only".
       test result updated.
 mysql-test/t/read_only_innodb.test
MDEV-136 Non-blocking "set read_only".
       test case added.
  sql/mysql_priv.h
MDEV-136 Non-blocking "set read_only".
        The close_cached_tables_set_readonly() declared.
  sql/set_var.cc
MDEV-136 Non-blocking "set read_only".
         Call close_cached_tables_set_readonly() for the read_only::set_var.
   sql/sql_base.cc
 MDEV-136 Non-blocking "set read_only".
         Parameters added to the close_cached_tables implementation,
         close_cached_tables_set_readonly declared.
         Prevent blocking on the transactional tables if the
         set_readonly_mode is on.

BUG#1000269: Wrong result (extra rows) with semijoin+materialization, IN subqueries, join_cache_level>0
- make make_cond_after_sjm() correctly handle OR clauses where one branch refers to the semi-join table
  while the other branch refers to the non-semijoin table.

sql/slave.cc:
  add mutex protection, like in sql_parse.cc

The problem is that we can't check null_value field of non-basic constant without the item execution.:

If we did nothing in resolving unique table conflict we should not retry (it leed to infinite loop).
Now we retry (recheck) unique table check only in case if we materialized a table.

- Let fix_semijoin_strategies_for_picked_join_order() set 
  POSITION::prefix_record_count for POSITION records that it copies from
  SJ_MATERIALIZATION_INFO::tables. 
  (These records do not have prefix_record_count set, because they are optimized
   as joins-inside-semijoin-nests, without full advance_sj_state() processing).  
 

  in greedy_search with LEFT JOINs and unique keys
- Backport the fix for BUG#806524 from MariaDB 5.3

The not_null_tables() of Item_func_not_all and Item_in_optimizer was inherited from
Item_func by mistake. It made the optimizer think that  subquery
predicates with ALL/ANY/IN were null-rejecting. This could trigger invalid
conversions of outer joins into inner joins.

It is problem of constant propagated to ref* access method (the problem was hiden by using debug binaries for testing).

The failures are  missing entries in the slow query log.  The reason for the failure  are sleep() calls  with short duration 10ms, which is less than the default system timer resolution for various WaitForXXXObject functions  (15.6 ms) and thus can't work reliably.
The fix is to make sleeps tiny bit longer (20ms from 10ms) in the test.

let x = `SELECT <something>`

The fix is to detect the condition "no active connection",  to report error and die.
Note, that the check for no active connection was already in place for ordinary commands, 
and was missing only for assign-variable command.

In 5.3 we substitute constants in ref access values it can't be null so we do not need add NOT NULL for early NULL filtering.

Optimization of aggregate functions detected constant under max() and evalueted it, but condition in the WHWRE clause (which is always FALSE) was not taken into account

The patch backports two patches from mysql 5.6:
- BUG#12640437: USING SQL_BUFFER_RESULT RESULTS IN A DIFFERENT QUERY OUTPUT
- Bug#12578908: SELECT SQL_BUFFER_RESULT OUTPUTS TOO MANY ROWS WHEN GROUP IS OPTIMIZED AWAY

Original comment:
-----------------
3714 Jorgen Loland	2012-03-01
      BUG#12640437 - USING SQL_BUFFER_RESULT RESULTS IN A DIFFERENT 
                     QUERY OUTPUT
      
      For all but simple grouped queries, temporary tables are used to
      resolve grouping. In these cases, the list of grouping fields is
      stored in the temporary table and grouping is resolved
      there (e.g. by adding a unique constraint on the involved
      fields). Because of this, grouping is already done when the rows
      are read from the temporary table.
      
      In the case where a group clause may be optimized away, grouping
      does not have to be resolved using a temporary table. However, if
      a temporary table is explicitly requested (e.g. because the
      SQL_BUFFER_RESULT hint is used, or the statement is
      INSERT...SELECT), a temporary table is used anyway. In this case,
      the temporary table is created with an empty group list (because
      the group clause was optimized away) and it will therefore not
      create groups. Since the temporary table does not take care of
      grouping, JOIN::group shall not be set to false in 
      make_simple_join(). This was fixed in bug 12578908. 
      
      However, there is an exception where make_simple_join() should
      set JOIN::group to false even if the query uses a temporary table
      that was explicitly requested but is not strictly needed. That
      exception is if the loose index scan access method (explain
      says "Using index for group-by") is used to read into the 
      temporary table. With loose index scan, grouping is resolved 
      by the access method. This is exactly what happens in this bug.

This is a backport of the fix for MySQL bug #13723054 in 5.6.

Original comment:
      The crash is caused by arbitrary memory area owerwriting in case of
      BLOB fields during attempt to copy BLOB field key image into record
      buffer(record buffer is too small to get BLOB key part image).
      note:
      QUICK_GROUP_MIN_MAX_SELECT can not work with BLOB fields
      because it uses record buffer as temporary buffer for key values
      however this case is filtered out by covering_keys() check
      in get_best_group_min_max() as BLOBs always require key length
      modificator in the key declaration and if the key has a BLOB
      then it can not be covered key.
      The fix is to use 'max_used_key_length' key length instead of 0.

Analysis:
Spcifically the crash in this bug was a result of the call to key_copy()
that copied the whole key, inlcuding the BLOB field which is not used
for index access. Copying the blob field overwrote memory as far as the
function parameter 'key_info'. As a result the contents of key_info was
all 0, which resulted in a crash when this key_info was accessed few
lines below in key_cmp().