MDEV-23855 changed the way how the page cleaner is signaled by
user threads. If a threshold is exceeded, a mini-transaction commit
would invoke buf_flush_ahead() in order to initiate page flushing
before all writers would eventually grind to halt in
log_free_check(), waiting for the checkpoint age to reduce.

However, buf_flush_ahead() would always initiate 'furious flushing',
making the buf_flush_page_cleaner thread write innodb_io_capacity_max
pages per batch, and sleeping no time between batches, until the
limit LSN is reached. Because this could saturate the I/O subsystem,
system throughput could significantly reduce during these
'furious flushing' spikes.

With this change, we introduce a gentler version of flush-ahead,
which would write innodb_io_capacity_max pages per second until
the 'soft limit' is reached.

buf_flush_ahead(): Add a parameter to specify whether furious flushing
is requested.

buf_flush_async_lsn: Similar to buf_flush_sync_lsn, a limit for
the less intrusive flushing.

buf_flush_page_cleaner(): Keep working until buf_flush_async_lsn
has been reached.

log_close(): Suppress a warning message in the event that a new log
is being created during startup, when old logs did not exist.
Return what type of page cleaning will be needed.

mtr_t::finish_write(): Also when m_log.is_small(), invoke log_close().
Return what type of page cleaning will be needed.

mtr_t::commit(): Invoke buf_flush_ahead() based on the return value of
mtr_t::finish_write().

buf_page_write_complete(): Reduce the buf_pool.mutex hold time,
and do not acquire buf_pool.flush_list_mutex at all.
Instead, mark blocks clean by setting oldest_modification to 1.
Dirty pages of temporary tables will be identified by the special
value 2 instead of the previous special value 1.
(By design of the ib_logfile0 format, actual LSN values smaller
than 2048 are not possible.)

buf_LRU_free_page(), buf_pool_t::get_oldest_modification()
and many other functions will remove the garbage (clean blocks)
from buf_pool.flush_list while holding buf_pool.flush_list_mutex.

buf_pool_t::n_flush_LRU, buf_pool_t::n_flush_list:
Replaced with non-atomic variables, protected by buf_pool.mutex,
to avoid unnecessary synchronization when modifying the counts.

export_vars: Remove unnecessary indirection for
innodb_pages_created, innodb_pages_read, innodb_pages_written.

In commit 7cffb5f6 (MDEV-23399)
the implementation of buf_flush_dirty_pages() was replaced with
a slow one, which would perform excessive scans of the
buf_pool.flush_list and make little progress.

buf_flush_list(), buf_flush_LRU(): Split from buf_flush_lists().
Vladislav Vaintroub noticed that we will not need to invoke
log_flush_task.wait() for the LRU eviction flushing.

buf_flush_list_space(): Replaces buf_flush_dirty_pages().
This is like buf_flush_list(), but operating on a single
tablespace at a time. Writes at most innodb_io_capacity
pages. Returns whether some of the tablespace might remain
in the buffer pool.

Vladislav Vaintroub suggested that invoking log_flush_up_to()
for every page could perform better than invoking a log write
between buf_pool.flush_list batches, like we started doing in
commit 3a9a3be1 (MDEV-23855).
This could depend on the sequence in which pages are being
modified. The buf_pool.flush_list is ordered by
oldest_modification, while the FIL_PAGE_LSN of the pages is
theoretically independent of that. In the pathological case,
we will wait for a log write before writing each individual page.

It turns out that we can defer the call to log_flush_up_to()
until just before submitting the page write. If the doublewrite
buffer is being used, we can submit a write batch of "future" pages
to the doublewrite buffer, and only wait for the log write right
before we are writing an already doublewritten page.
The next doublewrite batch will not be initiated before the last
page write from the current batch has completed.

When a future version introduces asynchronous writes if the log,
we could initiate a write at the start of a flushing batch, to
reduce waiting further.

It turns out that we had some unnecessary waits for no outstanding
write requests to exist. They were basically working around a
bug that was fixed in MDEV-25953.

On write completion callback, blocks will be marked clean.
So, it is sufficient to consult buf_pool.flush_list to determine
which writes have not been completed yet.

On FLUSH TABLES...FOR EXPORT we must still wait for all pending
asynchronous writes to complete, because buf_flush_file_space()
would merely guarantee that writes will have been initiated.

Cherry-picking only test case.

trx_undo_mem_create_at_db_start(): Relax too strict upgrade checks
that were introduced in
commit e46f76c9 (MDEV-15912).
On commit, pages will typically be set to TRX_UNDO_CACHED state.
Having the type TRX_UNDO_INSERT in such pages is common and
unproblematic; the type would be reset in trx_undo_reuse_cached().

trx_rseg_array_init(): On failure, clean up the rollback segments
that were initialized so far, to avoid an assertion failure later
during shutdown.

init_crypt_key(): On failure, set info->key_version to
ENCRYPTION_KEY_VERSION_INVALID.

log_crypt_101_read_block(): Refuse to attempt decryption if
info->key_version is ENCRYPTION_KEY_VERSION_INVALID.

This bug affected queries with views / derived_tables / CTEs whose
specifications were of the form
  (SELECT ... LIMIT <n>) ORDER BY ...
Units representing such specifications contains one SELECT_LEX structure
for (SELECT ... LIMIT <n>) and additionally SELECT_LEX structure for
fake_select_lex. This fact should have been taken into account in the
function mysql_derived_fill().

This patch has to be applied to 10.2 and 10.3 only.

This bug affected queries with views / derived_tables / CTEs whose
specifications were of the form
  (SELECT ... LIMIT <n>) ORDER BY ...
Units representing such specifications contains one SELECT_LEX structure
for (SELECT ... LIMIT <n>) and additionally SELECT_LEX structure for
fake_select_lex. This fact should have been taken into account in the
function mysql_derived_fill().

This patch has to be applied to 10.2 and 10.3 only.

trx_undo_report_row_operation(): Fix a race condition that was introduced
in commit f74023b9 (MDEV-15090).
We must not access undo_block after the page latch has been released
in mtr_t::commit(), because the block could be evicted or replaced.

In the merge commit d3e4fae7
a message about innodb_force_recovery was accidentally duplicated.

- Adding socket check for MariaDB/Mysql driver

Reviewed by: serg@mariadb.com

mytop fall-back to DBD::mysql if DBD::MariaDB is not available

Apply #1546

Let us simply refuse an upgrade from earlier versions if the
upgrade procedure was not followed. This simplifies the purge,
commit, and rollback of transactions.

Before upgrading to MariaDB 10.3 or later, a clean shutdown
of the server (with innodb_fast_shutdown=1 or 0) is necessary,
to ensure that any incomplete transactions are rolled back.
The undo log format was changed in MDEV-12288. There is only
one persistent undo log for each transaction.

Builds on travis-ci.org ceased on 2021-06-15.

see also 068246c0 and 690ae1de

see also 068246c0

see also a5f6eca5

spider tests use

--let $var= many;sql;statements
--eval $var

and this doesn't work in ps

and *never* disable tests in suite.pm based on $::opt_big_test,
this will make the test skipped both as too big (for ./mtr)
and as too small (for ./mtr --big --big).

MDEV-25867 main.trigger-trans failed in bb, Assertion `ticket->m_duration == MDL_EXPLICIT' failed in MDL_context::release_lock

release MDL on the trigger as early as possible, after everything that
cannot be done concurrently was done (under MDL), but before relocking
tables.

Do not execute user callback just after pwrite. Instead, submit user
function as task into thread pool. This way, the IO thread would not hog
aiocb, which is a limited (in Innodb) resource

- Make innodb_fts.misc_debug test case more stable.

Add fixed for tests mysqld--help,aix.rdiff and sysvars_server_notembedded,aix.rdiff

AIX couldn't compile in embedded mode so leaving sysvars_server_embedded
for later (if required).

In commit 1c35a3f6 a useless
computation that used the variable was removed.

Additional improvements aimed at improving operational
reliability of the SST scripts:

1) Script need to give rsync and stunnel a short time to
   terminate after "kill -9" before the first PID check
   using ps utility;
2) The temporary file used to create the binlog index could
   sometimes remain in the data directory if tar failed and
   then may be reused without being cleaned up (the next
   time when SST was run) - now it's fixed;
3) The temporary file used to build the binlog index is now
   created using mktemp and, if this variable is present in
   the configuration file, in tmpdir;
4) Checking the secret tag in SST via rsync is made faster
   and does not require creating a temporary file, which
   could remain in the data directory in case of failure;
5) Added "-F" option to grep to check the tag when using
   mariabackup/xtrabackup-v2 - to avoid possible collisions
   in case of special characters in the tag value (unlikely
   scenario, but the new check is more reliable).