Analysis:
The assert failed because the execution code for
partial matching is designed with the assumption that
NULLs on the left side are detected as early as possible,
and a NULL result is returned before any lookups are
performed at all.

However, in the case of an Item_cache object on the left
side, null was not detected properly, because detection
was done via Item::is_null(), which is not implemented at
all for Item_cache, and resolved to the default Item::is_null()
which always returns FALSE.

Solution:
Use the property Item::null_value instead of is_null(), which
is properly updated for Item_cache objects as well.

Generally, we should use only small letters for table names 
but here it's easier to fix with one --replace.

- cleaner code
- ability to change from using pointers to offsets at some point

- The problem was that Mrr_ordered_index_reader's interrupt_read() and resume_read() would 
  save and restore 1) index tuple  2) the rowid (as bytes returned by handler->position()).  Clustered 
  primary key columns were not saved/restored. 
  They are not explicitly present in the index tuple (i.e. table->key_info[secondary_key].key_parts 
  doesn't list them), but they are actually there, in particular 
  table->field[clustered_primary_key_member].part_of_key(secondary_key) == 1. Index condition pushdown
  code [correctly] uses the latter as inidication that pushed index condition can refer to clustered PK
  members. 

  The fix was to make interrupt_read()/resume_read() to save/restore clustered primary key members as well,
  so that we get correct values for them when evaluating pushed index condition.
[3rd attempt: remove the debugging aids, fix comments in testcase]

Analysis:
The reason for the crash was that the inner subquery was executed
via a scan on a final temporary table applied after all other
operations. This final operation is implemented by changing the
contents of the JOIN object of the subquery to represent a table
scan over the temp table. At the same time query optimization of
the outer subquery required evaluation of the inner subquery, which
happened before the actual EXPLAIN. The evaluation left the JOIN
object of the inner subquery in the changed state, where it represented
a table scan over a temp table, and EXPLAIN crashed because the temp
table is not associated with any table reference (TABLE_LIST object).
The reason the JOIN was not restored was because its saving/restoration
was controlled by the join->select_lex->uncacheable flag, which was
not set in the case of materialization.

Solution:
In the methods Item_in_subselect::[single | row]_value_transformer() set:
    select_lex->uncacheable|= UNCACHEABLE_EXPLAIN;
In addition, for symmetry, change:
    master_unit->uncacheable|= UNCACHEABLE_EXPLAIN;
instead of UNCACHEABLE_DEPENDENT because if a subquery was not
dependent initially, the changed methods do not change this
fact. The subquery may later become correlated if it is transformed
to an EXISTS query, but it may stay uncorrelated if executed via
materialization.

- Make DsMrr_impl::dsmrr_init() handle the case of 
   1. 1st MRR scan using DS-MRR strategy (i.e. doing key sorting and rowid sorting)
   2. 2nd MRR scan getting a buffer that's too small to fit one key element 
      and one rowid element, and so falling back to default MRR implementation
  In this case, dsmrr_init() is invoked with {primary_handler, secondary_handler}
  initialized for DS-MRR scan and have to reset them to be initialized for the
  default MRR scan.
(attempt 2, with simplified testcase)

- Make equality-substitution-for-ref-access code in JOIN::optimize() treat join_tab->ref.key_copy correctly
  (in the way create_ref_for_key() has filled it).

The bug in the function print_keyuse() caused crashes if
hash join could be used. It happened because the function
ignored the fact that KEYUSE structures could be created
for hash joins as well. 

sql/mysqld.cc:
  Fixed: optimize_join_buffer_size was missing in the description of possible
  options for the optimizer switch.
sql/sql_select.cc:
  Fixed: initialization for the field ref_table_rows of the KEYUSE structure was 
  missing (as a result of a lame merge).

- Make get_constant_key_infix() take into account that there may be SEL_TREEs with
  type=SEL_ARG::MAYBE_KEY, which it cannot process, because they are not real ranges
  but rather indications that we might have been able to construct a range if we had
  values for some other tables' fields. 
  (check_quick_select() already has such check)

client/readline.cc:
  Initialize not used variable (to kill wrong compiler warning)
mysql-test/suite/handler/aria.result:
  Updated test result
mysql-test/suite/handler/handler.inc:
  Changed index to ensure rows are in a fixed order
mysql-test/suite/handler/heap.result:
  Updated test result
mysql-test/suite/handler/innodb.result:
  Updated test result
mysql-test/suite/handler/myisam.result:
  Updated test result
plugin/handler_socket/handlersocket/Makefile.am:
  Use CXX flags to compile
sql/filesort.cc:
  Initialize variable that may be used
sql/log.cc:
  Initialize not used variable (to kill wrong compiler warning)
sql/opt_range_mrr.cc:
  Fixed cast to avoid compiler warning
storage/xtradb/fil/fil0fil.c:
  Added cast to avoid compiler warning

- Don't access THD::killed directly from ha_innodb.cc. This is forbidden because 
  THD has different membership (and so, different member offsets) in regular and embedded server.
  Access must be done through thd_killed() function.

- if we're interrupted by the user while in XtraDB, return the proper code.

even in the cases when there existed range/index-merge scans that
were cheaper than the full table scan.
This was a defect/bug of the implementation of mwl #128. 
Now hash join can work not only with full table scan of the joined
table, but also with full index scan, range and index-merge scans.
Accordingly, in the cases when hash join is used the column 'type'
in the EXPLAINs can contain now 'hash_ALL', 'hash_index', 'hash_range'
and 'hash_index_merge'. If hash join is coupled with a range/index_merge
scan then the columns 'key' and 'key_len' contain info not only on
the used hash index, but also on the indexes used for the scan.   

- Linking now with g++ instead of gcc with 'compile-dist' to solve problems with handlersocket/client
- Fixed bug in heap tables when doing handler read next-prev over last row


BUILD/compile-dist:
  - Linking now with g++ instead of gcc with 'compile-dist' to solve problems with handlersocket/client
cmd-line-utils/libedit/vi.c:
  Fixed compiler warning about not checking return value for write
mysql-test/r/index_intersect.result:
  Updated results (missed this file in my last push)
mysql-test/suite/handler/aria.result:
  Updated test results
mysql-test/suite/handler/handler.inc:
  Changed test to use read next/read prev on key where there are duplicates that can come in different order depending on system
  Added testing of read next-prev over last row and read prev-next around first row
mysql-test/suite/handler/heap.result:
  Updated test results
mysql-test/suite/handler/init.inc:
  More rows to test
mysql-test/suite/handler/innodb.result:
  Updated test results
mysql-test/suite/handler/interface.result:
  Updated test results
mysql-test/suite/handler/myisam.result:
  Updated test results
mysql-test/t/variables-big.test:
  Fixed test to not fail on windows
mysql-test/valgrind.supp:
  Removed not matching fun: to get rid of valgrind warning
storage/heap/hp_rfirst.c:
  Added state so that we know if we have an active position in the index.
storage/heap/hp_rkey.c:
  Added state so that we know if we have an active position in the index.
storage/heap/hp_rnext.c:
  Handle reading several next after finding the last row (this caused a crash before)
storage/heap/hp_rprev.c:
  Handle reading several prev after finding the first row (this caused a crash before)
storage/xtradb/buf/buf0buf.c:
  Fixed compiler warning about uninitialized value

dbug/dbug.c:
  Fixed compiler warnings on windows
mysql-test/r/index_intersect_innodb.result:
  Don't print number of rows as this varies
mysql-test/suite/funcs_1/r/processlist_val_no_prot.result:
  Update to use new State
mysql-test/suite/handler/heap.result:
  Update results
mysql-test/suite/handler/heap.test:
  Changed key used in test as the key 'b' will not guarantee order of the two last elements (as the key value is the same)
mysql-test/suite/pbxt/r/lock_multi.result:
  Update to use new State
mysql-test/t/index_intersect.test:
  Don't print number of rows as this varies
mysql-test/valgrind.supp:
  Added suppression for linux
mysys/hash.c:
  Fixed compiler warnings on windows
plugin/handler_socket/handlersocket/database.cpp:
  Fixed compiler warnings
sql-common/client_plugin.c:
  Changed variable to define to avoid compiler warnings when variable is not used
sql-common/my_time.c:
  Initialize all my_time elements to avoid compiler warnings
storage/oqgraph/ha_oqgraph.cc:
  Use right function (to avoid compiler warning)
storage/pbxt/src/table_xt.cc:
  Initialize variables (to avoid compiler warnings)

where bison runs in parallel with the same input and output files

- Cherrypick MBUG#688404  (PBXT crashes in debug/x64)
- Fix unixism (rm -rf) in the test suite_timeout
- Avoid plugin tests on Windows/embedded, plugins do not and will not work here

- Fixed compiler errors
- Modified Makefiles to be part of plugin directory
- Some minor changes in database.cpp to use the new MariaDB handler interface

Fix is to move extern "C" at the start of header file.

sql/multi_range_read.cc:
  Added printing of error if something goes wrong in get_next()
  (Not critical for this bug fix, but this was something that I noticed while testing and found missing)
storage/myisam/mi_rkey.c:
  Fixed wrong error number in mi_yield_and_check_if_killed()

Fix for lp:711565 "Index Condition Pushdown can make a thread hold MyISAM locks as well as be unKILLable for long time"
- In Maria/MyISAM: Release/re-acquire locks to give queries that wait on them a chance to make progress
- In Maria/MyISAM: Change from numeric constants to ICP_RES values.
- In Maria: Do check index condition in maria_rprev() (was lost in the merge/backport?)
- In Maria/MyISAM/XtraDB: Check if the query was killed, and return immediately if it was.

Added new storage engine error: HA_ERR_ABORTED_BY_USER, for handler to signal that it detected a kill of the query and aborted

Authors: Sergey Petrunia & Monty

include/my_base.h:
  Added HA_ERR_ABORTED_BY_USER, for handler to signal that it detected a kill of the query and aborted
include/my_handler.h:
  Added comment
mysql-test/r/myisam_icp.result:
  Updated test
mysql-test/t/myisam_icp.test:
  Drop used tables at start of test
  Added test case that can help with manual testing of killing index condition pushdown query.
mysys/my_handler_errors.h:
  Text for new storage engine error
sql/handler.cc:
  If engine got HA_ERR_ABORTED_BY_USER, send kill message.
sql/multi_range_read.cc:
  Return error code
storage/maria/ha_maria.cc:
  Added ma_killed_in_mariadb() to detect kill.
  Ensure that file->external_ref points to TABLE object.
storage/maria/ma_extra.c:
  Dummy test-if-killed for standalone
storage/maria/ma_key.c:
  If ma_check_index_cond() fails, set my_errno and info->cur_row.lastpos
storage/maria/ma_rkey.c:
  Release/re-acquire locks to give queries that wait on them a chance to make progress
  Check if the query was killed, and return immediately if it was
storage/maria/ma_rnext.c:
  Check if the query was killed, and return immediately if it was
  Added missing fast_ma_writeinfo(info)
storage/maria/ma_rnext_same.c:
  Check if the query was killed, and return immediately if it was
  Added missing fast_ma_writeinfo(info)
storage/maria/ma_rprev.c:
  Check if the query was killed, and return immediately if it was
  Added missing fast_ma_writeinfo(info) and ma_check_index_cond()
storage/maria/ma_search.c:
  Give error message if we find a wrong key
storage/maria/ma_static.c:
  Added pointer to test-if-killed function
storage/maria/maria_def.h:
  New prototypes
storage/myisam/ha_myisam.cc:
  Added mi_killed_in_mariadb()
  Ensure that file->external_ref points to TABLE object.
storage/myisam/mi_extra.c:
  Dummy test-if-killed for standalone
storage/myisam/mi_key.c:
  If ma_check_index_cond() fails, set my_errno and info->lastpos
storage/myisam/mi_rkey.c:
  Ensure that info->lastpos= HA_OFFSET_ERROR in case of error
  Release/re-acquire locks to give queries that wait on them a chance to make progress
  Check if the query was killed, and return immediately if it was
  Reorder code to do less things in case of error.
  Added missing fast_mi_writeinfo()
storage/myisam/mi_rnext.c:
  Check if the query was killed, and return immediately if it was
  Simplify old ICP code
  Added missing fast_ma_writeinfo(info)
storage/myisam/mi_rnext_same.c:
  Check if the query was killed, and return immediately if it was
  Added missing fast_mi_writeinfo(info)
storage/myisam/mi_rprev.c:
  Check if the query was killed, and return immediately if it was
  Simplify error handling of ICP
  Added missing fast_mi_writeinfo(info)
storage/myisam/mi_search.c:
  Give error message if we find a wrong key
storage/myisam/mi_static.c:
  Added pointer to test-if-killed function
storage/myisam/myisamdef.h:
  New prototypes
storage/xtradb/handler/ha_innodb.cc:
  Added DB_SEARCH_ABORTED_BY_USER and ha_innobase::is_thd_killed()
  Check if the query was killed, and return immediately if it was
storage/xtradb/handler/ha_innodb.h:
  Added prototype
storage/xtradb/include/db0err.h:
  Added DB_SEARCH_ABORTED_BY_USER
storage/xtradb/include/row0mysql.h:
  Added possible ICP errors
storage/xtradb/row/row0sel.c:
  Use ICP errors instead of constants.
  Detect if killed and return B_SEARCH_ABORTED_BY_USER