One can set @@global.max_user_connections to -1 to block anyone, except SUPER user, to login.
If max_user_connection is 0, one can't change it without a restart (needed to get user connections counting to work correctly)


mysql-test/r/system_mysql_db.result:
  Changed max_user_connections to handle negative numbers.
mysql-test/r/user_limits-2.result:
  New test case that one can't change max_user_connection if it was 0
mysql-test/r/user_limits.result:
  Fixed wrong error messages.
mysql-test/r/variables.result:
  Store / restore max_user_connections (needed as there is now a --master.opt file that changes it)
mysql-test/t/subselect_mat_cost-master.opt:
  Enable slow query log (as this test found some errors in slow query logging)
mysql-test/t/user_limits-2.test:
  New test case that one can't change max_user_connection if it was 0
mysql-test/t/user_limits-master.opt:
  Set max_user_connections (as one can't change it if it was 0)
mysql-test/t/user_limits.test:
  Test max_user_connections -1
mysql-test/t/variables-master.opt:
  Set max_user_connections (as one can't change it if it was 0)
mysql-test/t/variables.test:
  Set/restore max_user_connections
scripts/Makefile.am:
  Add a text message to mysql_fix_privilege_tables.sql that it's automaticly generated
scripts/mysql_system_tables.sql:
  Change max_user_connections to signed
scripts/mysql_system_tables_fix.sql:
  Change max_user_connections to signed
sql/item_func.cc:
  Change SHOW_INT to be signed.
  (Needed for max_user_connections and it's probably a bug that it was not originally signed)
sql/log.cc:
  Remove some code that was not needed (All these variables are reset at start of query)
sql/mysql_priv.h:
  Made max_user_connections signed.
  Added max_user_connections_checking
sql/mysqld.cc:
  Added max_user_connections_checking so that we know if max_user_connections was 0 at startup
  (Which means that we will not do connection counting for accounts that don't have user resource limits)
  Set thd->start_utime at same time as thr_create_utime. (Before start_utime could be < thr_create_utime which lead to wrong query counting)
sql/set_var.cc:
  Don't allow one to change 'max_user_connections' if it was 0 at startup.
sql/sql_acl.cc:
  Change user_connection counting to be negative.
sql/sql_connect.cc:
  If max_user_connections is < 0 then only SUPER user can login.
  Fixed wrong variable names for error messages.
  Fixed wrong initial value for questions.
  Set thd->start_utime and thd->thr_create_utime at startup.  Needed to get time_out_user_resource_limits() to work.
sql/sql_show.cc:
  SHOW_INT is now negative
sql/sql_yacc.yy:
  Support negative values for MAX_USER_CONNECTIONS
sql/structs.h:
  Make user connect counting work with signed numbers.

Reset 'examined_rows_count' in union to not count same rows twice

mysql-test/r/subselect_mat_cost.result:
  Test also slow query logging
mysql-test/t/subselect_mat_cost.test:
  Test also slow query logging
sql/sql_union.cc:
  Reset 'examined_rows_count' in union to not count same rows twice

- If USER is given, all threads for that user is signaled
- If SOFT is used then the KILL will not be sent to the handler. This can be used to not interrupt critical things in the handler like 'REPAIR'.

Internally added more kill signals. This gives us more information of why a query/connection was killed.
- KILL_SERVER is used when server is going down. In this case the users gets ER_SHUTDOWN as the reason connection was killed.
- Changed signals to number in correct order, which makes it easier to test how the signal should affect the code.
- New error message ER_CONNECTION_KILLED if connection was killed by 'KILL CONNECTION'. Before we got error ER_SHUTDOWN.

Changed names of not used parameters KILL_QUERY & KILL_CONNCTION to mysql_kill() to not conflict with defines in the server


include/mysql.h.pp:
  Updated file
include/mysql_com.h:
  Changed names of not used parameters KILL_QUERY & KILL_CONNCTION to mysql_kill() to not conflict with defines in the server
mysql-test/r/kill.result:
  Added test of KILL USER
mysql-test/suite/rpl/r/rpl_stm_000001.result:
  Updated error code
mysql-test/suite/rpl/t/rpl_stm_000001.test:
  Updated error codes
mysql-test/t/flush_read_lock_kill.test:
  Updated error codes
mysql-test/t/kill.test:
  Added test of KILL USER
plugin/handler_socket/handlersocket/database.cpp:
  Removed THD:: from KILL
sql/debug_sync.cc:
  Removed THD:: from KILL
sql/event_scheduler.cc:
  Removed THD:: from KILL
sql/filesort.cc:
  Removed THD:: from KILL
sql/ha_ndbcluster_binlog.cc:
  Removed THD:: from KILL
sql/handler.cc:
  Removed THD:: from KILL
  Simplify code.
sql/lex.h:
  Added new keywords HARD | SOFT
sql/log.cc:
  Removed THD:: from KILL
  Added testing of new error ER_CONNECTION_KILLED
sql/log_event.cc:
  Removed THD:: from KILL
  Added testing of new error ER_CONNECTION_KILLED
sql/mysql_priv.h:
  Added new prototypes
sql/mysqld.cc:
  Removed THD:: from KILL
  Use KILL_SERVER_HARD signal on shutdown.
sql/scheduler.cc:
  Removed THD:: from KILL
  Simplify test if connection should be killed
sql/share/errmsg.txt:
  New error message ER_CONNECTION_KILLED
sql/slave.cc:
  Removed THD:: from KILL
sql/sp_head.cc:
  Removed THD:: from KILL
sql/sql_base.cc:
  Removed THD:: from KILL
sql/sql_cache.cc:
  Removed THD:: from KILL
sql/sql_class.cc:
  Removed THD:: from KILL
  Added killed_errno()
  Only signal kill to storage engine if HARD bit is set.
sql/sql_class.h:
  Move KILL options out from THD to make them easier to use in sql_yacc.yy
sql/sql_connect.cc:
  Removed THD:: from KILL
sql/sql_delete.cc:
  Removed THD:: from KILL
sql/sql_error.cc:
  Removed THD:: from KILL
sql/sql_insert.cc:
  Removed THD:: from KILL
  Simplifed testing if thread is killed.
sql/sql_lex.h:
  Added kill options to st_lex
sql/sql_load.cc:
  Removed THD:: from KILL
sql/sql_parse.cc:
  Added kill options to st_lex
  Simplifed and optimzed testing of thd->killed at end of query
  Added support for KILL USER
  Extended sql_kill() to allow use of more kill signals.
sql/sql_repl.cc:
  Removed THD:: from KILL
sql/sql_show.cc:
  Removed THD:: from KILL
  Simplied testing if query/connection was killed
sql/sql_table.cc:
  Removed THD:: from KILL
sql/sql_update.cc:
  Removed THD:: from KILL
sql/sql_yacc.yy:
  Added support for new KILL syntax: KILL [HARD|SOFT] [CONNECTION|QUERY] [ID | USER user_name]
storage/archive/ha_archive.cc:
  Simplify compilation
storage/maria/ha_maria.cc:
  Removed THD:: from KILL

- The problem was that Item_direct_view_ref and its embedded Item_field were getting incorrect
  value of item->used_tables() after fix_fields() in the second and subsequent EXECUTE.
- Made relevant fixes in Item_field::fix_fields() and find_field_in_tables(), so that the 
  Item_field gets the correct attributes.

BUG##849717: Crash in Item_func::fix_fields on second execution of a prepared statement with semijoin
- If convert_join_subqueries_to_semijoins() decides to wrap Item_in_subselect in Item_in_optimizer, 
  it should do so in prep_on_expr/prep_where, too, as long as they are present.
  There seems to be two possibilities of how we arrive in this function:
  - prep_on_expr/prep_where==NULL, and will be set later by simplify_joins()
  - prep_on_expr/prep_where!=NULL, and it is a copy_and_or_structure()-made copy of on_expr/where.
  the latter can happen for some (but not all!) nested joins. This bug was that we didn't handle this case.

(Code taken from 5.5)

- Mrr_ordered_index_reader::interrupt_read() and resume_read() should 
  save/restore not just index lookup tuple, but entire index tuple.
  Key parts that are not used for index lookup can be still used in
  pushed index condition. Failure to save/restore will cause the index
  condition to be evaluated over the wrong values.

Give proper error to client on shutdown.

configure.in:
  Increased version number
mysql-test/mysql-test-run.pl:
  Ignore errors that one can get while running with --mysqld=--log-warnings=2
mysql-test/r/variables.result:
  Remember original value of log_warnings
mysql-test/suite/rpl/r/rpl_idempotency.result:
  Ignore errors that one can get while running with --mysqld=--log-warnings=2
mysql-test/suite/rpl/t/rpl_idempotency.test:
  Ignore errors that one can get while running with --mysqld=--log-warnings=2
mysql-test/t/variables.test:
  Remember original value of log_warnings
sql/mysqld.cc:
  Give proper error to close_connection() on shutdown
storage/maria/ha_maria.cc:
  Added missing DBUG_RETURN

Fixed that automatic killing of delayed insert thread (in flush, alter table etc) will not abort auto-repair of MyISAM table.
Give more information when finding an error in a MyISAM table.
When killing system thread, use KILL_SYSTEM_THREAD instead of KILL_CONNECTION to make it easier to ignore the signal in sensitive context (like auto-repair)
Added new kill level: KILL_SERVER that will in the future to be used to signal killed by shutdown.
Add more warnings about killed connections when warning level > 3

include/myisamchk.h:
  Added counting of printed info/notes
mysys/mf_iocache.c:
  Remove duplicate assignment
sql/handler.cc:
  Added test of KILL_SERVER
sql/log.cc:
  Ignore new 'kill' error ER_NEW_ABORTING_CONNECTION when requesting query error code.
sql/mysqld.cc:
  Add more warnings for killed connections when warning level > 3
sql/scheduler.cc:
  Added checks for new kill signals
sql/slave.cc:
  Ignore new kill signal ER_NEW_ABORTING_CONNECTION
sql/sp_head.cc:
  Fixed assignment to bool
  Added testing of new kill signals
sql/sql_base.cc:
  Use KILL_SYSTEM_THREAD to auto-kill system threads
sql/sql_class.cc:
  Add more warnings for killed connections when warning level > 3
  thd_killed() now ignores KILL_BAD_DATA and THD::KILL_SYSTEM_THREAD as these should not abort sensitive operations.
sql/sql_class.h:
  Added KILL_SYSTEM_THREAD and KILL_SERVER
sql/sql_connect.cc:
  Added handling of KILL_SERVER
sql/sql_insert.cc:
  Use KILL_SYSTEM_THREAD to auto-kill system threads
  Added handling of KILL_SERVER
sql/sql_parse.cc:
  Add more warnings for killed connections when warning level > 3
  Added checking that thd->abort_on_warning is reset at end of query.
sql/sql_show.cc:
  Update condition for when a query is 'killed'
storage/myisam/ha_myisam.cc:
  Added counting of info/notes printed
storage/myisam/mi_check.c:
  Always print an an error if we find data errors when checking/repairing a MyISAM table.
  When a repair was killed, don't retry repair.
  Added assert if sort_get_next_record() returned an error without an error message.
  Removed nonsence check "if (sort_param->read_cache.error < 0)" in repair.
storage/myisam/myisamchk.c:
  Added counting of notes printed
storage/pbxt/src/thread_xt.cc:
  Better error message.

- The bug was caused by outer join being incorrectly converted into inner because of 
  invalid return values of Item_direct_view_ref::not_null_tables().
- Provided a correct Item_direct_view_ref::not_null_tables() function.

- Let join buffering code correctly take into account rowids needed 
  by DuplicateElimination when it is calculating minimum record sizes.
- In JOIN_CACHE::write_record_data, added asserts that prevent us from 
  writing beyond the end of the buffer.

The problem was that optimization code did not take into account later feature when instad of NOT before BETWEEN it has negated flag into the Item_func_between inherited from Item_func_neg_opt. So optimizer tried process NOT BETWEEN as BETWEEN.

The patch just switches off the optimisation for NOT BETWEEN as it was before when NOT function was really used.

remove incorrect DBUG_ASSERT().
Fix incorrectly used cmp_item::get_comparator() in Item_func_case and Item_equal

For any query JOIN::optimize() should call the method
SELECT::save_leaf_tables after the last transformation
that utilizes the statement memory rather than the 
execution memory.
  

- Make subquery_types_allow_materialization() detect a case where 
  create_tmp_table() would create a blob column which would make it 
  impossible to use materialization
  Non-semi-join materialization worked because it detected that this case
  and felt back to use IN->EXISTS. Semi-join Materialization cannot easily
  fallback, so we have to detect this case early.

- Don't use join buffering for tables that are within ranges that are 
  covered by LooseScan strategy.

- get_bound_sj_equalities() would produce incorrect bitmap when non-first 
  equality was bound, which resulted in invalid LooseScan plans.

  
  ALL subquery should return TRUE if subquery rowa set is empty independently
  of left part.  The problem was that Item_func_(eq,ne,gt,ge,lt,le) do not
  call execution of second argument if first is NULL no in this case subquery
  will not be executed and when Item_func_not_all calls any_value() of the
  subquery or aggregation function which report that there was rows. So for
  NULL < ALL (SELECT...) result was FALSE instead of TRUE.
  
  Fix is just swapping of arguments of Item_func_(eq,ne,gt,ge,lt,le) (with
  changing the operation if it is needed) so that result will be the same
  (for examole a < b is equal to b > a). This fix exploit the fact that
  first argument will be executed in any case.