This patch introduces support for the system variable eq_range_index_dive_limit
that existed in MySQL starting from 5.6. The variable sets a limit for
index dives into equality ranges. Index dives are performed by optimizer
to estimate the number of rows in range scans. Index dives usually provide
good estimate but they are pretty expensive. To estimate the number of rows
in equality ranges statistical data on indexes can be employed. Its usage gives
not so good estimates but it's cheap. So if the number of equality dives
required by an index scan exceeds the set limit no dives for equality
ranges are performed by the optimizer for this index.

As the new system variable is introduced in a stable version the default
value for it is set to a special value meaning there is no limit for the number
of index dives performed by the optimizer.

The patch partially uses the MySQL code for WL 5957
'Statistics-based Range optimization for many ranges'.

The MySQL 5.7 TRUNCATE TABLE is inherently incompatible
with hot backup, because it is creating and deleting a separate
log file, and it is not writing redo log for all changes of the
InnoDB data dictionary tables. Refuse to create a corrupted backup
if the unsafe form of TRUNCATE was executed.

Note: Undo log tablespace truncation cannot be detected easily.
Also it is incompatible with backup, for similar reasons.

xtrabackup_backup_func(): "Subscribe to" the log events before
the first invocation of xtrabackup_copy_logfile().

recv_parse_or_apply_log_rec_body(): If the function pointer
log_truncate is set, invoke it to report MLOG_TRUNCATE.

Remove the logic for skipping the test if a log checkpoint occurred,
and the logic for tolerating failures. Thanks to MDEV-16791,
MLOG_INDEX_LOAD is supposed to always work.

Amend commit b853b4fd
that was reverted in commit 29150e23.

recv_parse_log_recs(): Do check for corrupted redo log or file
system before checking for len==0, but only read *ptr if
it is not past the end of the buffer (end_ptr).

recv_parse_log_rec(): Report incorrect redo log type
in a consistent way with recv_parse_or_apply_log_rec_body().
This is a follow-up to commit f30c5af4.

The Pool poisoning that was introduced in MDEV-15030 introduced
race conditions in AddressSanitizer builds, because concurrent
poisoning and unpoisoning were not prevented by any synchronization
primitive.

Pool::get(): Protect the unpoisoning by m_lock_strategy.

Pool::mem_free(): Protect the poisoning by m_lock_strategy.

Pool::putl(): Renamed from put(), because now the caller is
responsible for invoking m_lock_strategy.

If trx_free() and trx_create_low() were called while a call to
trx_reference() was pending, we could get a reference to a wrong
transaction object.

trx_reference(): Return NULL if the trx->id no longer matches.

lock_trx_release_locks(): Assign trx->id = 0, so that trx_reference()
will not return a reference to this object.

trx_cleanup_at_db_startup(): Assign trx->id = 0.

assert_trx_is_free(): Assert !trx->n_ref. Assert trx->id == 0,
now that it will be cleared as part of a transaction commit.

Also, replace reverse iteration with forward iteration.

lock_table_has(): Remove a redundant condition.

Allocate trx->lock.rec_pool and trx->lock.table_pool directly from trx_t.
Remove unnecessary use of std::vector.

In order to do this, move some definitions from lock0priv.h to
lock0types.h, so that ib_lock_t will not be an opaque type.

aws_key_management needs current directory to be datadir during
initalization, it scans current directory for encrypted keys.

Fix is to ensure, that plugin initialization in mariabackup happens
after the call to my_setwd(mysql_real_data_home).

Fix a race condition in the test.

The test causes simulated server crashes with DBUG_SUICIDE();.

It also relies on transactions that were committed right before the
crash to be visible after the crash (that is, it requires durability).

Run the test with transaction durability enabled: set
rocksdb-flush-log-at-trx-commit=1.

The package libmariadbclient18 contains the dialog.so plugin, which also
the new libmariadb3 ships. As they both use the exact same path the latter
must be marked as a with Breaks and Replaces relations ship.

Note: This fix is conservative hack for stable releases 10.2 and 10.3.
In 10.4, the development release at the time, we will clean up how the
libmariadb3 packaging and it's -compat packages are done to match that
what is done in downstream Debian official.

recv_parse_log_recs(): Do not check for corruption before
checking for end-of-log-buffer. For some reason, adding the
check to the logical-looking place would cause intermittent
recovery failures in the tests innodb.innodb-index and
innodb_gis.rtree_compress2.

recv_parse_log_recs(): Check for corruption before checking for
end-of-log-buffer.

mlog_parse_initial_log_record(), page_cur_parse_delete_rec():
Flag corruption for out-of-bounds values, and let the caller
dump the corrupted redo log extract.

If recv_sys_justify_left_parsing_buf() has been invoked, it is possible
that recv_previous_parsed_rec_offset is after the current offset.
In this case, we must not dump any bytes before the current record.

If the LOG_BLOCK_HDR_DATA_LEN field is corrupted, scanning the
log records could fail in strange ways. It is better to validate
the field as part of validating each log block.

Display the log record type in hexadecimal, not binary.

warning: suggest a space before ‘;’ or explicit braces around empty body in ‘for’ statement

update the test to the new (correct) result

make mysqld_multi to use same rules for my.cnf directories
that all other tools are using (see my_default.c).

  filamtxt.cpp: DOSFAM::RenameTempFile: Change sprintf to snprintf.
  filamvct.cpp: VECFAM::RenameTempFile: Change sprintf to snprintf.
  javaconn.cpp:
    Add JAVAConn::GetUTFString function.
    Use it instead of env->GetStringUTFChars.
    Fix wrong identation.
  javaconn.h: Add GetUTFString declaration.
  jdbconn.cpp:
    Use GetUTFString function instead of env->GetStringUTFChars.
  jmgoconn.cpp:
    Use GetUTFString function instead of env->GetStringUTFChars.
    Fix wrong identation.
  jsonudf.cpp: change 139 to BMX line 4631.
  tabjmg.cpp:
    Add ReleaseStringUTF.
    Fix wrong identation.
  tabpivot.cpp: Fix wrong identation.
  tabutil.cpp: TDBPRX::GetSubTable: Change sprintf to snprintf.
  modified:   storage/connect/filamtxt.cpp
  modified:   storage/connect/filamvct.cpp
  modified:   storage/connect/javaconn.cpp
  modified:   storage/connect/javaconn.h
  modified:   storage/connect/jdbconn.cpp
  modified:   storage/connect/jmgoconn.cpp
  modified:   storage/connect/jsonudf.cpp
  modified:   storage/connect/tabjmg.cpp
  modified:   storage/connect/tabpivot.cpp
  modified:   storage/connect/tabutil.cpp

- Fix MDEV-16895 CONNECT engine's get_error_message can cause buffer
                 overflow and server crash with long queries
  ha_connect_cc: Update version.
    get_error_message: Remove charset conversion.
  modified:   storage/connect/ha_connect.cc

- Fix a server crash on inserting bigint to a JDBC table
  JDBConn::SetUUID:
    Suppress check on ctyp that causes a server crash because ctyp
    can be negative and this triggers an DEBUG_ASSERT on return.
  modified:   storage/connect/jdbconn.cpp

- Update jdbc.result
  mysql-test/connect/r/jdbc.result: Recorded to reflect a message change.
  modified:   storage/connect/mysql-test/connect/r/jdbc.result

The charset of temporary storage (Item_func_json_insert::tmp_js)
  was not properly set.

Item_func_json_value::val_str() produced string of wrong charset.

rw_lock_get_debug_info(): Remove. This function is inherently unsafe
to use, because the copied pointers can become stale between
rw_lock_debug_mutex_exit() and the dereferencing of the pointer in
the caller.