sends down UPDATE statement together with current database name.

Add MTR test for UPDATE.

Multi-UPDATE first sends SELECT to collect constrainsts for the records
to be updated. By default this SELECT uses SH that doesn't suit this.
Add if-block to guard against multi-UPDATE in create_SH().

        Renamed select handler control knob.

        Updated test suite.

      Removed unused code.

    Add a knob to disable Select handler.

        syncronize the schema list at MDB FE and CLX BE.

        Add support for RENAME TABLE.

        Fixed a double free bug in discover_table_details.

texts.

Replaced fixed size uchar arrays for buffers with memory allocations.

Fixed MDB crash in discover_table_details with CX unavailable.

Related to MDEV-21769.

Related to MDEV-21769.

After the '.so' one is supposed to use the directory name, like we have
correctly in all old man pages:
  mysql_client_test_embedded.1:.so man1/mysql_client_test.1
  mysql_embedded.1:.so man1/mysql.1
  mysqltest_embedded.1:.so man1/mysqltest.1

This change adds the 'man1/' component so the link has the correct format.
Actually using man links is a deprecated practice and using symlinks
would be better, but that can be fixed in a later commit.

From https://www.debian.org/doc/debian-policy/ch-docs.html#manual-pages:
> If one man page needs to be accessible via several names it is better
> to use a symbolic link than the .so feature

Detected via Lintian errors:
  E: mariadb-server-10.5: bad-so-link-within-manual-page usr/share/man/man1/mariadb-show.1.gz
  E: mariadb-client-10.5: bad-so-link-within-manual-page usr/share/man/man1/mariadb-binlog.1.gz
  E: mariadb-client-10.5: bad-so-link-within-manual-page usr/share/man/man1/mariadb-plugin.1.gz

Related to MDEV-21769.

This fixes errors like:

  $ LC_ALL=en_US.UTF-8 MANROFFSEQ='' MANWIDTH=80 \
    man --warnings -E UTF-8 -l -Tutf8 -Z mysql-test-run.pl.1 > /dev/null

  troff: <standard input>:246: warning [p 2, 6.0i, div '3tbd1,1', 0.3i]: can't break line
  troff: <standard input>:275: warning [p 2, 6.0i, div '3tbd6,1', 0.8i]: can't break line

Related to MDEV-21769.

Related to MDEV-21769.

Added CYCLE ... RESTRICT (nonstandard) clause to recursive CTE.

The following parameters are deprecated:

  innodb-background-scrub-data-uncompressed
  innodb-background-scrub-data-compressed
  innodb-background-scrub-data-interval
  innodb-background-scrub-data-check-interval

Removed scrubbing code completely(btr0scrub.h, btr0scrub.cc)
Removed information_schema.innodb_tablespaces_scrubbing tables
Removed the scrubbing logic from fil_crypt_thread()

When a InnoDB data file page is freed, its contents becomes garbage,
and any storage allocated in the data file is wasted. During flushing,
InnoDB initializes the page with zeros if scrubbing is enabled. If the
tablespace is compressed then InnoDB should punch a hole else ignore the
flushing of the freed page.

buf_page_t:
- Replaced the variable file_page_was_freed, init_on_flush in buf_page_t
with status enum variable.
- Changed all debug assert of file_page_was_freed to DBUG_ASSERT
of buf_page_t::status

Removed buf_page_set_file_page_was_freed(),
buf_page_reset_file_page_was_freed().

buf_page_free(): Newly added function which takes X-lock on the page
before marking the status as FREED. So that InnoDB flush handler can
avoid concurrent flush of the freed page. Also while flushing the page,
InnoDB make sure that redo log which does freeing of the page also written
to the disk. Currently, this function only marks the page as FREED if
it is in buffer pool

buf_flush_freed_page(): Newly added function which initializes zeros
asynchorously if innodb_immediate_scrub_data_uncompressed is enabled.
Punch a hole to the file synchorously if page_compressed is enabled.
Reset the io_fix to NORMAL. Release the block from flush list and
associated mutex before writing zeros or punch a hole to the file.

buf_flush_page(): Removed the unnecessary usage of temporary
variable "flush"

fil_io(): Introduce new parameter called punch_hole. It allows fil_io()
to punch the hole to the file for the given offset.

buf_page_create(): Let the callers assign buf_page_t::status.
Every caller should eventually invoke mtr_t::init().

fsp_page_create(): Remove the unused mtr_t parameter.

In all other callers of buf_page_create() except fsp_page_create(),
before invoking mtr_t::init(), invoke
mtr_t::sx_latch_at_savepoint() or mtr_t::x_latch_at_savepoint().

mtr_t::init(): Initialize buf_page_t::status also for the temporary
tablespace (when redo logging is disabled), to avoid assertion failures.