SQL: reverted NATURAL JOIN fix #161 (deprecated by #383)

versioning.truncate is affected in embedded mode

SQL: fixed selecion of handlerton by respecting partitioning

Merge branch '10.3' into trunk

MDEV-14632 Assertion `!((new_col->prtype ^ col->prtype) & ~256U)' failed in row_log_table_apply_convert_mrec

SQL: add exclusive lock to ADD/DROP SYSTEM VERSIONING clauses

This is needed because Online DDL is not working yet for such queries.

Instead of updating global counter, calculate Threads_running on the fly.
All threads having command != COM_SLEEP are included.

Behaviour changes:

Previously SHOW STATUS and SHOW GLOBAL STATUS returned the same values
representing global status. Now SHOW STATUS always returns 1 indicating that
current session has 1 thread running.

Previously only threads that were executing dispatch_command() or running events
were accounted by Threads_running. Now it is rough equivalent of
SELECT COUNT(*) FROM INFORMATION_SCHEMA.PROCESSLIST WHERE state!='Sleep'

SQL: remove unneeded assertion
SQL: disallow set sys_trx fields in INSERT ... SELECT

Fixes by @midenok.

Cleaned up by @midenok.

The problem was that multi_range_read_info_const() called
multi_range_key_create_key() which changed m_part_spec.start_part,
while there was an activ table scan ongoing.

Fixed by copying and restoring m_part_spec around
multi_range_key_create_calls()

SQL: disallow ADD SYSTEM VERSIONING for system-versioned tables

Part #2: Take into accont the fact that three binary collations that
we handle are technically NOPAD collations

Disallow use of NOPAD collations in indexed columns.

first, and we do not not care whether client has received all data.

This is a TCP optimization to avoid TIME_WAIT in TCP connection teardown.

This patch would abort connection on timeout, which usually happens when
client reads a large result set, at slower pace then the server can
write.

The patch also cleans up socket timeout handling, so that Windows
is consistent with another platforms (using nonblocking socket IO
 + waiting in poll/select on single socket, rather than setsockopt).
This makes identifying timeouts easier.


Also removed the superficial shutdown() before closesocket() in a few
places where it was used, because it  was never needed , and
reportedly breaks SO_LINGER on Windows.

Merge branch '10.3' into trunk

When the transaction isolation level is SERIALIZABLE, or when
a locking read is performed in the REPEATABLE READ isolation level,
InnoDB must lock delete-marked records in order to prevent another
transaction from inserting something.

However, at READ UNCOMMITTED or READ COMMITTED isolation level or
when the parameter innodb_locks_unsafe_for_binlog is set, the
repeatability of the reads does not matter, and there is no need
to lock any records.

row_search_mvcc(): Skip locks on delete-marked committed records upfront,
instead of invoking row_unlock_for_mysql() afterwards. The unlocking
never worked for secondary index records.