This is 11.0 part of the fix: in 11.0, get_costs_for_tables() calls
best_access_path() for all possible tables, for each call it saves
a POSITION object with the access method and "loose_scan_pos"
POSITION object.
The latter is saved even if there is no possible LooseScan plan. Saving
is done by copying POSITION objects which may generate a spurious
UBSan error.

Problem was an overflow when calculating number of join cache refills.

This was caused of two minor issues:
- get_quick_record_count() returned the number of rows for range with
  least cost, when it should have returned the minum number of rows
  for any range.
- When changing REF to RANGE, we also changed records_out, which
  should not be done (number of records in the result will not
  change).

The above change can cause a small change in row estimates where the
optimizer chooses a clustered key with more rows than a range one
secondary key (unlikely case).

In Loose_scan_opt::save_to_position, initialize
POSITION::firstmatch_with_join_buf.

The code in create_internal_tmp_table() didn't take into account that
now temporary (derived) tables may have multiple indexes:

- one index due to duplicate removal
   = In this example created by conversion of big-IN(...) into subquery
   = this index might be converted into a "unique constraint" if the key
     length is too large.
- one index added by derived_with_keys optimization.

Make create_internal_tmp_table() handle multiple indexes.

Before this patch, use of a unique constraint was indicated in
TABLE_SHARE::uniques. This was ok as unique constraint was the only index
in the table. Now it's no longer the case so TABLE_SHARE::uniques is removed
and replaced with an in-memory-only flag HA_UNIQUE_HASH.

This patch is based on Monty's patch.
Co-Author: Monty <monty@mariadb.org>

This makes it easier to run test on just events.

This makes it easier to run test on just the MRG_MYISAM engine.

Other things:
- Renamed merge-big.test to flush_corruption.test as it does not
  have anything to do with merge tables.

The problem was that for merge tables without any underlaying tables the
block size was 0, which the code could not handle.

Fixed by ensuring that MERGE tables never have a block size of 0.
Fixed also a wrong assumption of number of seeks needed to scan
merge tables.

Introduces @@optimizer_switch flag: hash_join_cardinality

When this option is on, use EITS statistics to produce tighter bounds
for hash join output cardinality.

This patch is an extension / replacement to a similar patch in 10.6

New features:
- optimizer_switch hash_join_cardinality is on by default
- records_out is set to fanout when HASH is used
- Fixed bug in is_eits_usable: The function did not work with views

rtr_ins_enlarge_mbr(): Relax the assertion that was added in
commit f27e9c89
to cover also table-rebuilding DDL. We only need
btr_cur->rtr_info->thr for acquiring R-tree locks,
and the thread that is executing a DDL operation has exclusive
access to the being-built index or the copy of the being-rebuilt table.

Set the lock wait timeout to 1 beforehand, and reset it afterwards, to
avoid lock conflict caused by opening the same table twice in case of
self-reference.

- assign spider->share early when !new_share
- remove locking before spider_share_init_{sts,crd}

Extracted out common subroutines, gave more meaningful names etc,
added comments etc.

Also:
- Documented active servers load balancing reads, and other fields in
  SPIDER_SHARE etc.
- Removed commented out code
- Documented and refactored self-reference check
- Removed some unnecessary functions
- Renamed unhelpful roop_count
- Refactored spider_get_{sts,crd}, where we turn get_type into an enum
- Cleaned up spider_mbase_handler::show_table_status() and
  spider_mbase_handler::show_index()

Deb-autobakes where failing with:

dh_missing: warning: usr/share/mysql/mysql-test/mysql-test-run exists in debian/tmp but is not installed to anywhere
dh_missing: warning: usr/share/mysql/mysql-test/mtr exists in debian/tmp but is not installed to anywhere
dh_missing: warning: usr/share/mysql/mysql-test/mariadb-test-run exists in debian/tmp but is not installed to anywhere
dh_missing: warning: usr/share/mysql/mysql-test/mysql-test-run.pl exists in debian/tmp but is not installed to anywhere

Add all to mariadb-test.install and remove mariadb-test.links

Applying b98375f9 instead of 9b32e4b1 for version 10.5-10.8.
Applying 5075f4e0 instead of 9b32e4b1 for version 10.9+.

AWK is used in autobake-debs.sh for printing information
about created DEB packages.

This can be rewrite with bash inner commands read and echo.

AWK in used in Debian SysV-init and postinst scripts to determine
is there enough space starting MariaDB database or create new
database to target destination.

These AWK scripts can be rewrited to use pure SH or help
using Coreutils which is mandatory for usage of MariaDB currently.

Reasoning behind this is to get rid of one very less used dependency

Extend the portability of ANALYZE FORMAT=JSON by using the microsecond
timer if cycles isn't available.

Reviewer: Sergei Petrunia <sergey@mariadb.com>

make the compile-time logic in my_timer_cycles() also #define
MY_TIMER_ROUTINE_CYCLES to indicate which implementation it is using.
Then, make my_timer_init() use MY_TIMER_ROUTINE_CYCLES.

This leaves us with just one set of compile-time #if's which determine
how we read time in #cycles.

Reviewer (and commit message author): Sergei Petrunia <sergey@mariadb.com>

This fixes up commit e3f6e1c9

log_free_check(): Assert that the caller must not hold
exclusive lock_sys.latch. This was the case for calls from
ibuf_delete_for_discarded_space(). This caused a deadlock with
another thread that would be holding a latch on a dirty page
that would need to be written so that the checkpoint would advance
and log_free_check() could return. That other thread was waiting
for a shared lock_sys.latch.

fil_delete_tablespace(): Do not invoke ibuf_delete_for_discarded_space()
because in DDL operations, we will be holding exclusive lock_sys.latch.

trx_t::commit(std::vector<pfs_os_file_t>&), innodb_drop_database(),
row_purge_remove_clust_if_poss_low(), row_undo_ins_remove_clust_rec(),
row_discard_tablespace_for_mysql():
Invoke ibuf_delete_for_discarded_space() on the deleted tablespaces after
releasing all latches.

page_cleaner_flush_pages_recommendation(): If dirty_pct is
between innodb_max_dirty_pages_pct_lwm
and innodb_max_dirty_pages_pct,
scale the effort relative to how close we are to
innodb_max_dirty_pages_pct.

The previous formula was missing a multiplication by 100.

Tested by: Axel Schwenke

followup for d1a46c68