For non-semi-join subquery optimization we do a cost based decision between
Materialisation and IN -> EXIST transformation. The issue in this case is that for IN->EXIST transformation
we run JOIN::reoptimize with the IN->EXISt conditions and we come up with a new query plan. But when we compare
the cost with Materialization, we make the decision to chose Materialization so we need to restore the query plan
for Materilization.
The saving and restoring for keyuse array and join_tab keyuse is only done when we have atleast
one element in the keyuse_array , we are now changing to do it even for 0 elements to main the generality.

gdb's "set args" equivalent for lldb would be "settings set target.run-args",
however it doesn't play well with double dashed args (--).

           upon SELECT .. LIMIT 0

The code must differentiate between a SELECT with contradictory
WHERE/HAVING and one with LIMIT 0.
Also for the latter printed 'Zero limit' instead of 'Impossible where'
in the EXPLAIN output.

It should work ok on all Unixes, but on Windows ,only worked by accident
in the past, with client not being Unicode safe.

It stopped working with Visual Studio 2017 15.7 update now.

When Item_insert_value needs a dummy field,
use zero-length Field_string, not Field_null.
The latter isn't compatible with CREATE ... SELECT.

Analyze core independently of max-save-datadir and max-save-core setting.

Increment $num_saved_cores only if core was actually saved.

"Move any core files from e.g. mysqltest" independently of
max-save-datadir setting. Note: it may overwrite core from mysqld, which
might not be desired (it did work this way even before).

MDEV-654 Assertion `share->now_transactional' failed in flush_log_for_bitmap on concurrent workload with Aria tables

Problem was that we the bitmap needs to be flushed before disabling
logging of redo entires, as writing the bitmap to disk by
background checkpoint may cause redo entries.

QUERY_DML_NO_SELECT flag added.

a better fix

fix another similar line

followup for 7828ba0d

multiple times with different arguments.

If the ON expression of an outer join is an OR formula with one
of the disjunct being a constant formula then the expression
cannot be null-rejected if the constant formula is true. Otherwise
it can be null-rejected and if so the outer join can be converted
into inner join. This optimization was added in the patch for
mdev-4817. Yet the code had a defect: if the query was used in
a stored procedure with parameters and the constant item contained
some of them then the value of this constant item depended on the
values of the parameters. With some parameters it may be true,
for others not. The validity of conversion to inner join is checked
only once and it happens only for the first call of procedure.
So if the  parameters in the first call allowed the conversion it
was done and next calls used the transformed query though there
could be calls whose parameters made the conversion invalid.

Fixed by cheking whether the constant disjunct in the ON expression
originally contained an SP parameter. If so the expression is not
considered as null-rejected. For this check a new item's attribute
was intruduced: Item::with_param. It is calculated for each item
by fix fields() functions.
Also moved the call of optimize_constant_subqueries() in
JOIN::optimize after the call of simplify_joins(). The reason
for this is that after the optimization introduced by the patch
for mdev-4817 simplify_joins() can use the results of execution
of non-expensive constant subqueries and this is not valid.

MDEV-13699: Assertion `!new_field->field_name.str || strlen(new_field->field_name.str) == new_field->field_name.length' failed in create_tmp_table on 2nd execution of PS with semijoin

The problem was that SJ (semi-join) used secondary list (array) of subquery select list. The items there was prepared once then cleaned up (but not really freed from memory because it was made in statement memory).
Original list was not prepared after first execution because select was removed by conversion to SJ.
The solution is to use original list but prepare it first.

in a specially crafted invalid packet, one can get end_pos < pos here

disable online alter add primary key for innodb, if the
table is opened/locked more than once in the current connection

(see assert in ha_innobase::add_index())

test case

Any expensive WHERE condition for a table-less query with
implicit aggregation was lost. As a result the used aggregate
functions were calculated over a non-empty set of rows even
in the case when the condition was false.

Also clarify which --{no-,}default* options, must be first.

Sample output:
$  client/mysql --help
client/mysql  Ver 15.1 Distrib 5.5.59-MariaDB, for Linux (x86_64) using readline 5.1
Copyright (c) 2000, 2017, Oracle, MariaDB Corporation Ab and others.

Usage: client/mysql [OPTIONS] [database]

Default options are read from the following files in the given order:
/etc/my.cnf /etc/mysql/my.cnf ~/.my.cnf
The following groups are read: mysql client client-server client-mariadb
The following options may be given as the first argument:
--print-defaults          Print the program argument list and exit.
--no-defaults             Don't read default options from any option file.
The following specify which files/groups are read (specified before other options):
--defaults-file=#         Only read default options from the given file #.
--defaults-extra-file=#   Read this file after the global files are read.
--defaults-group-suffix=# Additionally read default groups with # appended as a suffix.

tests running from build directory:
TEST: print defaults ignored as not first
$ sql/mysqld  --no-defaults --print-defaults --lc-messages-dir=${PWD}/sql/share

TEST: no startup occurs as --print-defaults specified
$ sql/mysqld  --print-defaults --lc-messages-dir=${PWD}/sql/share
sql/mysqld would have been started with the following arguments:
--lc-messages-dir=/home/dan/repos/build-mariadb-5.5/sql/share

TEST: default args can't be anywhere
$ client/mysql --user=bob  --defaults-file=/etc/my.cnf
client/mysql: unknown variable 'defaults-file=/etc/my.cnf'
$ client/mysql --user=bob  --defaults-group-suffix=.group
client/mysql: unknown variable 'defaults-group-suffix=.group'

/etc/my.cnf:
[client-server.group]
socket=/var/lib/mysql-multi/group/mysqld.sock
user=bob

/etc/my.other.cnf:
socket=/var/lib/mysql-other/mysqld.sock

TEST: defaults file read and suffix also applied
$  client/mysql  --defaults-file=/etc/my.other.cnf  --defaults-group-suffix=.group
ERROR 2002 (HY000): Can't connect to local MySQL server through socket '/var/lib/mysql-other/mysqld.sock' (2)

TEST: defaults extra file
$ client/mysql  --defaults-extra-file=/etc/my.other.cnf  --defaults-group-suffix=.group
ERROR 2002 (HY000): Can't connect to local MySQL server through socket '/var/lib/mysql-other/mysqld.sock' (2)

condition fixed.

handler::ha_create_handler_files shouldn't call the
mark_trx_read_write() for the temporary table.

MDEV-15624 Changing the default character set to utf8mb4 changes query evaluation in a very surprising way

warning: format '%p' expects argument of type 'void *', but argument 4 has type 'long int'

For this case we have a view that is mergeable but we are not able to merge it in the
parent select because that would exceed the maximum tables allowed in the join list, so we
materialise this view
TABLE_LIST::dervied is NULL for such views, it is only set for views which have ALGORITHM=TEMPTABLE
Fixed by making sure TABLE_LIST::derived is set for views that could not be merged

A simple patch fixing the problem in 5.5.
Note, a full patch was previously fixed to 10.3.

Conversion of a subquery to a semi-join is blocked when we have an
IN subquery predicate in the on_expr of an outer join. Currently this
scenario is handled but the cases when an IN subquery predicate is wrapped
inside a Item_in_optimizer item then this blocking is not done.

Detection of first execution of PS fixed.
More debug info.

For the query having an IN subquery with no tables, we were converting the subquery with an expression between
the left part and the select list of the subquery . This can give incorrect results when we have a condition
in the subquery with a dual table (as this is treated as a no table).

The fix is that we don't do this conversion when we have conds in the subquery with a dual table.

mem_heap_create_block(): Poison the payload area until
mem_heap_alloc() unpoisons it.

Learn both valgrind and asan to catch this bug:

  mem_heap_t* heap = mem_heap_create(1024);
  byte* p = reinterpret_cast<byte*>(heap) + sizeof(mem_heap_t);
  *p = 123;

Overflows of the last allocation in a block will be catched too.

mem_heap_create_block(): poison newly allocated memory

Backport from 10.2

The issue is that we are creating a materialised table with key of length 0 which is incorrect, we should
disable materialisation for such a case.

              PREBUILT->TABLE->N_MYSQL_HANDLES_OPENED == 1

ANALYSIS:
=========

Adding unique index to a InnoDB table which is locked as
mutliple instances may trigger an InnoDB assert.

When we add a primary key or an unique index, we need to
drop the original table and rebuild all indexes. InnoDB
expects that only the instance of the table that is being
rebuilt, is open during the process. In the current
scenario we have opened multiple instances of the table.
This triggers an assert during table rebuild.
'Locked_tables_list' encapsulates a list of all
instances of tables locked by LOCK TABLES statement.

FIX:
===
We are now temporarily closing all the instances of the
table except the one which is being altered and later
reopen them via Locked_tables_list::reopen_tables().