This is only a placeholder that allows an implementation later
during the development of MariaDB, so that downgrade to an earlier
version (with this code) will be possible.
We want to be able to zero out freed pages to reduce write amplification,
and to scrub old data. Zeroing out the pages is optional, not mandatory
for correctness. After all, the MLOG_INIT_FREE_PAGE record can only be
emitted for pages that are marked free in the allocation bitmap page.

Use ibuf_bitmap_page_init() only during recovery.

fsp_fill_free_list(): Initialize the FIL_PAGE_TYPE using MLOG_2BYTES.
The page contents will already have been zeroed out by
MLOG_INIT_FILE_PAGE2.

ibuf_bitmap_init_apply(): Replaces ibuf_parse_bitmap_init().

rec_init_offsets(): Relax a debug assertion that is too strict
during the execution of btr_cur_instant_init_low().

Fix for failures on galera.galera_sst_mysqldump

Test galera_sst_mysqldump could fail occasionally due certification failure. Enforcing stricter causality checks by removing wsrep_sync_wait=0 from test configuration.

MySQL 5.7 introduced the class page_size_t and increased the size of
buffer pool page descriptors by introducing this object to them.

Maybe the intention of this exercise was to prepare for a future
where the buffer pool could accommodate multiple page sizes.
But that future never arrived, not even in MySQL 8.0. It is much
easier to manage a pool of a single page size, and typically all
storage devices of an InnoDB instance benefit from using the same
page size.

Let us remove page_size_t from MariaDB Server. This will make it
easier to remove support for ROW_FORMAT=COMPRESSED (or make it a
compile-time option) in the future, just by removing various
occurrences of zip_size.

instant_alter_column_possible(): allow non-rebuilding operations for
ROW_FORMAT=COMPRESSED

Updated wsrep-lib to galera cache encryption implementation

test a multi-auth with a missing auth plugin on the client

update (and simplify) plugin_auth.test to match

introduce the syntax

... IDENTIFIED { WITH | VIA }
      plugin [ { USING | AS } auth ]
 [ OR plugin [ { USING | AS } auth ]
 [ OR ... ]]

Server will try auth plugins in the specified order until the first
success. No protocol changes, server uses the existing "switch plugin"
packet.

The auth chain is stored in json as

  "auth_or":[{"plugin":"xxx","authentication_string":"yyy"},
             {},
             {"plugin":"foo","authentication_string":"bar"},
            ...],
  "plugin":"aaa", "authentication_string":"bbb"

Note:
* "auth_or" implies that there might be "auth_and" someday;
* one entry in the array is an empty object, meaning to take plugin/auth
  from the main json object. This preserves compatibility with
  the existing mysql.global_priv table and with the mysql.user view.
  This entry is preferrably a mysql_native_password plugin for a
  non-empty mysql.user.password column.

SET PASSWORD is supported and changes the password for the *first*
plugin in the chain that has a notion of a "password"

add DEPRECATED() warning for variables with "deprecated" in the
help text. Remove redundant initializers.

if auth_root_socket is set, root user should be using unix_socket

Followup for 4abb8216

Revert the side effect of 7c40996c.
Do not convert password hash to its binary representation when a user
entry is loaded. Do it lazily on the first authenticatation attempt.

As a collateral - force all authentication plugins to follow the
protocol and read_packet at least once before accessing info->username
(username is not available before first client handshake packet is read).

Fix PAM and GSSAPI plugins to behave.

add tests

Add a system variable spider_slave_trx_isolation.
- spider_slave_trx_isolation
  The transaction isolation level when Spider table is used by slave SQL thread.
  -1 : OFF
   0 : READ UNCOMMITTED
   1 : READ COMMITTED
   2 : REPEATABLE READ
   3 : SERIALIZABLE
  The default value is -1

Miscellaneous Spider typos

Change default value of the followings
quick_mode 0 -> 3
quick_page_size 100 -> 1024

Add the following parameter for limiting result page size by byte
- quick_page_byte(qpb)
  Number of bytes in a page when acquisition one by one.
  When quick_mode is 1 or 2, Spider stores at least 1 record even if
  quick_page_byte is smaller than 1 record. When quick_mode is 3,
  quick_page_byte is used for judging using temporary table.
  That is given to priority when server parameter spider_quick_page_byte
  is set.
  The default value is 10485760

Fix "out of sync" issue at using quick_mode = 1 or 2

The fields of the temporary table were not created in create_tmp_table function. Because item->const_item() was true. But the temporary tables that is created by Spider are always used all columns. So Spider should call create_tmp_table function with TMP_TABLE_ALL_COLUMNS flag.

Store original charset during client authentication, and restore it for
COM_RESET_CONNECTION

The default value for eq_range_index_dive_limit is set to 10

No need to lowercase table names on case-sensitive file systems, as the
cache won't contain the 'lowercased' table anyway. And it prevents the
UPPERCASE.frm from being deleted.

Problem:
=======
Mariabackup incremental prepare creates new tablespace when it encounter
new tablespace. It sets the intial size as FIL_IBD_FILE_INITIAL_SIZE (4).
But while applying redo log, it tries to access 5th page and then
it leads to out of tablespace error.

Fix:
===
While parsing the redo log record, track FSP_SIZE in recv_spaces for the
respective space id. Assign the recv_size for the tablespace when it
is loaded. Extend the tablespace depends on recv_size while applying
the redo log record.

- Added retry logic if validation of first page fails with checksum
mismatch.

Do not try to write ER_SHUTDOWN error message to socket, when it is forcefully closed by the shutdown.
This will avoid the race condition (attempt to write to closed socket,  if connection shuts down by itself).

MDEV-18426: Most of the mtr tests in the galera_3nodes suite fail