The buffer pool refactoring in MDEV-15053 and MDEV-22871 shifted
the performance bottleneck to the page flushing.
The configuration parameters will be changed as follows:
innodb_lru_flush_size=32 (new: how many pages to flush on LRU eviction)
innodb_lru_scan_depth=1536 (old: 1024)
innodb_max_dirty_pages_pct=90 (old: 75)
innodb_max_dirty_pages_pct_lwm=75 (old: 0)
Note: The parameter innodb_lru_scan_depth will only affect LRU
eviction of buffer pool pages when a new page is being allocated. The
page cleaner thread will no longer evict any pages. It used to
guarantee that some pages will remain free in the buffer pool. Now, we
perform that eviction 'on demand' in buf_LRU_get_free_block().
The parameter innodb_lru_scan_depth(srv_LRU_scan_depth) is used as follows:
* When the buffer pool is being shrunk in buf_pool_t::withdraw_blocks()
* As a buf_pool.free limit in buf_LRU_list_batch() for terminating
the flushing that is initiated e.g., by buf_LRU_get_free_block()
The parameter also used to serve as an initial limit for unzip_LRU
eviction (evicting uncompressed page frames while retaining
ROW_FORMAT=COMPRESSED pages), but now we will use a hard-coded limit
of 100 or unlimited for invoking buf_LRU_scan_and_free_block().
The status variables will be changed as follows:
innodb_buffer_pool_pages_flushed: This includes also the count of
innodb_buffer_pool_pages_LRU_flushed and should work reliably,
updated one by one in buf_flush_page() to give more real-time
statistics. The function buf_flush_stats(), which we are removing,
was not called in every code path. For both counters, we will use
regular variables that are incremented in a critical section of
buf_pool.mutex. Note that show_innodb_vars() directly links to the
variables, and reads of the counters will *not* be protected by
buf_pool.mutex, so you cannot get a consistent snapshot of both variables.
The following INFORMATION_SCHEMA.INNODB_METRICS counters will be
removed, because the page cleaner no longer deals with writing or
evicting least recently used pages, and because the single-page writes
have been removed:
* buffer_LRU_batch_flush_avg_time_slot
* buffer_LRU_batch_flush_avg_time_thread
* buffer_LRU_batch_flush_avg_time_est
* buffer_LRU_batch_flush_avg_pass
* buffer_LRU_single_flush_scanned
* buffer_LRU_single_flush_num_scan
* buffer_LRU_single_flush_scanned_per_call
When moving to a single buffer pool instance in MDEV-15058, we missed
some opportunity to simplify the buf_flush_page_cleaner thread. It was
unnecessarily using a mutex and some complex data structures, even
though we always have a single page cleaner thread.
Furthermore, the buf_flush_page_cleaner thread had separate 'recovery'
and 'shutdown' modes where it was waiting to be triggered by some
other thread, adding unnecessary latency and potential for hangs in
relatively rarely executed startup or shutdown code.
The page cleaner was also running two kinds of batches in an
interleaved fashion: "LRU flush" (writing out some least recently used
pages and evicting them on write completion) and the normal batches
that aim to increase the MIN(oldest_modification) in the buffer pool,
to help the log checkpoint advance.
The buf_pool.flush_list flushing was being blocked by
buf_block_t::lock for no good reason. Furthermore, if the FIL_PAGE_LSN
of a page is ahead of log_sys.get_flushed_lsn(), that is, what has
been persistently written to the redo log, we would trigger a log
flush and then resume the page flushing. This would unnecessarily
limit the performance of the page cleaner thread and trigger the
infamous messages "InnoDB: page_cleaner: 1000ms intended loop took 4450ms.
The settings might not be optimal" that were suppressed in
commit d1ab89037a unless log_warnings>2.
Our revised algorithm will make log_sys.get_flushed_lsn() advance at
the start of buf_flush_lists(), and then execute a 'best effort' to
write out all pages. The flush batches will skip pages that were modified
since the log was written, or are are currently exclusively locked.
The MDEV-13670 message "page_cleaner: 1000ms intended loop took" message
will be removed, because by design, the buf_flush_page_cleaner() should
not be blocked during a batch for extended periods of time.
We will remove the single-page flushing altogether. Related to this,
the debug parameter innodb_doublewrite_batch_size will be removed,
because all of the doublewrite buffer will be used for flushing
batches. If a page needs to be evicted from the buffer pool and all
100 least recently used pages in the buffer pool have unflushed
changes, buf_LRU_get_free_block() will execute buf_flush_lists() to
write out and evict innodb_lru_flush_size pages. At most one thread
will execute buf_flush_lists() in buf_LRU_get_free_block(); other
threads will wait for that LRU flushing batch to finish.
To improve concurrency, we will replace the InnoDB ib_mutex_t and
os_event_t native mutexes and condition variables in this area of code.
Most notably, this means that the buffer pool mutex (buf_pool.mutex)
is no longer instrumented via any InnoDB interfaces. It will continue
to be instrumented via PERFORMANCE_SCHEMA.
For now, both buf_pool.flush_list_mutex and buf_pool.mutex will be
declared with MY_MUTEX_INIT_FAST (PTHREAD_MUTEX_ADAPTIVE_NP). The critical
sections of buf_pool.flush_list_mutex should be shorter than those for
buf_pool.mutex, because in the worst case, they cover a linear scan of
buf_pool.flush_list, while the worst case of a critical section of
buf_pool.mutex covers a linear scan of the potentially much longer
buf_pool.LRU list.
mysql_mutex_is_owner(), safe_mutex_is_owner(): New predicate, usable
with SAFE_MUTEX. Some InnoDB debug assertions need this predicate
instead of mysql_mutex_assert_owner() or mysql_mutex_assert_not_owner().
buf_pool_t::n_flush_LRU, buf_pool_t::n_flush_list:
Replaces buf_pool_t::init_flush[] and buf_pool_t::n_flush[].
The number of active flush operations.
buf_pool_t::mutex, buf_pool_t::flush_list_mutex: Use mysql_mutex_t
instead of ib_mutex_t, to have native mutexes with PERFORMANCE_SCHEMA
and SAFE_MUTEX instrumentation.
buf_pool_t::done_flush_LRU: Condition variable for !n_flush_LRU.
buf_pool_t::done_flush_list: Condition variable for !n_flush_list.
buf_pool_t::do_flush_list: Condition variable to wake up the
buf_flush_page_cleaner when a log checkpoint needs to be written
or the server is being shut down. Replaces buf_flush_event.
We will keep using timed waits (the page cleaner thread will wake
_at least_ once per second), because the calculations for
innodb_adaptive_flushing depend on fixed time intervals.
buf_dblwr: Allocate statically, and move all code to member functions.
Use a native mutex and condition variable. Remove code to deal with
single-page flushing.
buf_dblwr_check_block(): Make the check debug-only. We were spending
a significant amount of execution time in page_simple_validate_new().
flush_counters_t::unzip_LRU_evicted: Remove.
IORequest: Make more members const. FIXME: m_fil_node should be removed.
buf_flush_sync_lsn: Protect by std::atomic, not page_cleaner.mutex
(which we are removing).
page_cleaner_slot_t, page_cleaner_t: Remove many redundant members.
pc_request_flush_slot(): Replaces pc_request() and pc_flush_slot().
recv_writer_thread: Remove. Recovery works just fine without it, if we
simply invoke buf_flush_sync() at the end of each batch in
recv_sys_t::apply().
recv_recovery_from_checkpoint_finish(): Remove. We can simply call
recv_sys.debug_free() directly.
srv_started_redo: Replaces srv_start_state.
SRV_SHUTDOWN_FLUSH_PHASE: Remove. logs_empty_and_mark_files_at_shutdown()
can communicate with the normal page cleaner loop via the new function
flush_buffer_pool().
buf_flush_remove(): Assert that the calling thread is holding
buf_pool.flush_list_mutex. This removes unnecessary mutex operations
from buf_flush_remove_pages() and buf_flush_dirty_pages(),
which replace buf_LRU_flush_or_remove_pages().
buf_flush_lists(): Renamed from buf_flush_batch(), with simplified
interface. Return the number of flushed pages. Clarified comments and
renamed min_n to max_n. Identify LRU batch by lsn=0. Merge all the functions
buf_flush_start(), buf_flush_batch(), buf_flush_end() directly to this
function, which was their only caller, and remove 2 unnecessary
buf_pool.mutex release/re-acquisition that we used to perform around
the buf_flush_batch() call. At the start, if not all log has been
durably written, wait for a background task to do it, or start a new
task to do it. This allows the log write to run concurrently with our
page flushing batch. Any pages that were skipped due to too recent
FIL_PAGE_LSN or due to them being latched by a writer should be flushed
during the next batch, unless there are further modifications to those
pages. It is possible that a page that we must flush due to small
oldest_modification also carries a recent FIL_PAGE_LSN or is being
constantly modified. In the worst case, all writers would then end up
waiting in log_free_check() to allow the flushing and the checkpoint
to complete.
buf_do_flush_list_batch(): Clarify comments, and rename min_n to max_n.
Cache the last looked up tablespace. If neighbor flushing is not applicable,
invoke buf_flush_page() directly, avoiding a page lookup in between.
buf_flush_space(): Auxiliary function to look up a tablespace for
page flushing.
buf_flush_page(): Defer the computation of space->full_crc32(). Never
call log_write_up_to(), but instead skip persistent pages whose latest
modification (FIL_PAGE_LSN) is newer than the redo log. Also skip
pages on which we cannot acquire a shared latch without waiting.
buf_flush_try_neighbors(): Do not bother checking buf_fix_count
because buf_flush_page() will no longer wait for the page latch.
Take the tablespace as a parameter, and only execute this function
when innodb_flush_neighbors>0. Avoid repeated calls of page_id_t::fold().
buf_flush_relocate_on_flush_list(): Declare as cold, and push down
a condition from the callers.
buf_flush_check_neighbor(): Take id.fold() as a parameter.
buf_flush_sync(): Ensure that the buf_pool.flush_list is empty,
because the flushing batch will skip pages whose modifications have
not yet been written to the log or were latched for modification.
buf_free_from_unzip_LRU_list_batch(): Remove redundant local variables.
buf_flush_LRU_list_batch(): Let the caller buf_do_LRU_batch() initialize
the counters, and report n->evicted.
Cache the last looked up tablespace. If neighbor flushing is not applicable,
invoke buf_flush_page() directly, avoiding a page lookup in between.
buf_do_LRU_batch(): Return the number of pages flushed.
buf_LRU_free_page(): Only release and re-acquire buf_pool.mutex if
adaptive hash index entries are pointing to the block.
buf_LRU_get_free_block(): Do not wake up the page cleaner, because it
will no longer perform any useful work for us, and we do not want it
to compete for I/O while buf_flush_lists(innodb_lru_flush_size, 0)
writes out and evicts at most innodb_lru_flush_size pages. (The
function buf_do_LRU_batch() may complete after writing fewer pages if
more than innodb_lru_scan_depth pages end up in buf_pool.free list.)
Eliminate some mutex release-acquire cycles, and wait for the LRU
flush batch to complete before rescanning.
buf_LRU_check_size_of_non_data_objects(): Simplify the code.
buf_page_write_complete(): Remove the parameter evict, and always
evict pages that were part of an LRU flush.
buf_page_create(): Take a pre-allocated page as a parameter.
buf_pool_t::free_block(): Free a pre-allocated block.
recv_sys_t::recover_low(), recv_sys_t::apply(): Preallocate the block
while not holding recv_sys.mutex. During page allocation, we may
initiate a page flush, which in turn may initiate a log flush, which
would require acquiring log_sys.mutex, which should always be acquired
before recv_sys.mutex in order to avoid deadlocks. Therefore, we must
not be holding recv_sys.mutex while allocating a buffer pool block.
BtrBulk::logFreeCheck(): Skip a redundant condition.
row_undo_step(): Do not invoke srv_inc_activity_count() for every row
that is being rolled back. It should suffice to invoke the function in
trx_flush_log_if_needed() during trx_t::commit_in_memory() when the
rollback completes.
sync_check_enable(): Remove. We will enable innodb_sync_debug from the
very beginning.
Reviewed by: Vladislav Vaintroub
The setting innodb_lock_schedule_algorithm=VATS that was introduced
in MDEV-11039 (commit 021212b525)
causes conflicting exclusive locks to be incorrectly granted to
two transactions. Specifically, in lock_rec_insert_by_trx_age()
the predicate !lock_rec_has_to_wait_in_queue(in_lock) would hold even
though an active transaction is already holding an exclusive lock.
This was observed between two DELETE of the same clustered index record.
The HASH_DELETE invocation in lock_rec_enqueue_waiting() may be related.
Due to lack of progress in diagnosing the problem, we will remove the
option. The unsafe option was enabled by default between
commit 0c15d1a6ff (MariaDB 10.2.3)
and the parent of
commit 1cc1d0429d (MariaDB 10.2.17, 10.3.9),
and it was deprecated in
commit 295e2d500b (MariaDB 10.2.34).
Regretfully, the parameter innodb_log_checksums was introduced
in MySQL 5.7.9 (the first GA release of that series) by
mysql/mysql-server@af0acedd88
which partly replaced a parameter that had been introduced in 5.7.8
mysql/mysql-server@22ba38218e
as innodb_log_checksum_algorithm.
Given that the CRC-32C operations are accelerated on many processor
implementations (AMD64 with SSE4.2; since MDEV-22669 also on IA-32
with SSE4.2, POWER 8 and later, ARMv8 with some extensions)
and by lookup tables when only generic SISD instructions are available,
there should be no valid reason to disable checksums.
In MariaDB 10.5.2, as a preparation for MDEV-12353, MDEV-19543 deprecated
and ignored the parameter innodb_log_checksums altogether. This should
imply that after a clean shutdown with innodb_log_checksums=OFF one
cannot upgrade to MariaDB Server 10.5 at all.
Due to these problems, let us deprecate the parameter innodb_log_checksums
and honor it only during server startup.
The command SET GLOBAL innodb_log_checksums will always set the
parameter to ON.
The usage message for the innodb_compression_algorithm system variable
did not list snappy, which was added as an optional compression algorithm
in MariaDB 10.1.3 and might actually work since
commit 90c52e5291 (MDEV-12615)
in MariaDB 10.1.24.
Unfortunately, we will include also unavailable compression algorithms
in the list, because ENUM parameters allow numeric values, and we do
not want innodb_compression_algorithm=3 to change meaning depending on
the way how the source code was compiled.
The parameters innodb_thread_concurrency and innodb_commit_concurrency
were useful years ago when both computing resources and the implementation
of some shared data structures were limited. MySQL 5.0 or 5.1 had trouble
scaling beyond 8 concurrent connections. Most of the scalability bottlenecks
have been removed since then, and the transactions per second delivered
by MariaDB Server 10.5 should not dramatically drop upon exceeding the
'optimal' number of connections.
Hence, enabling any concurrency throttling for InnoDB actually makes
things worse. We have seen many customers mistakenly setting this to a
small value like 16 or 64 and then complaining the server was slow.
Ignoring the parameters allows us to remove some normally unused code
and data structures, which could slightly improve performance.
innodb_thread_concurrency, innodb_commit_concurrency,
innodb_replication_delay, innodb_concurrency_tickets,
innodb_thread_sleep_delay, innodb_adaptive_max_sleep_delay:
Deprecate and ignore; hard-wire to 0.
The column INFORMATION_SCHEMA.INNODB_TRX.trx_concurrency_tickets
will always report 0.
The rw_lock_s_lock() calls for the buf_pool.page_hash became a
clear bottleneck after MDEV-15053 reduced the contention on
buf_pool.mutex. We will replace that use of rw_lock_t with a
special implementation that is optimized for memory bus traffic.
The hash_table_locks instrumentation will be removed.
buf_pool_t::page_hash: Use a special implementation whose API is
compatible with hash_table_t, and store the custom rw-locks
directly in buf_pool.page_hash.array, intentionally sharing
cache lines with the hash table pointers.
rw_lock: A low-level rw-lock implementation based on std::atomic<uint32_t>
where read_trylock() becomes a simple fetch_add(1).
buf_pool_t::page_hash_latch: The special of rw_lock for the page_hash.
buf_pool_t::page_hash_latch::read_lock(): Assert that buf_pool.mutex
is not being held by the caller.
buf_pool_t::page_hash_latch::write_lock() may be called while not holding
buf_pool.mutex. buf_pool_t::watch_set() is such a caller.
buf_pool_t::page_hash_latch::read_lock_wait(),
page_hash_latch::write_lock_wait(): The spin loops.
These will obey the global parameters innodb_sync_spin_loops and
innodb_sync_spin_wait_delay.
buf_pool_t::freed_page_hash: A singly linked list of copies of
buf_pool.page_hash that ever existed. The fact that we never
free any buf_pool.page_hash.array guarantees that all
page_hash_latch that ever existed will remain valid until shutdown.
buf_pool_t::resize_hash(): Replaces buf_pool_resize_hash().
Prepend a shallow copy of the old page_hash to freed_page_hash.
buf_pool_t::page_hash_table::n_cells: Declare as Atomic_relaxed.
buf_pool_t::page_hash_table::lock(): Explain what prevents a
race condition with buf_pool_t::resize_hash().
For no good reason, innodb_encryption_threads was limited to
4,294,967,295. Expectedly, the server would crash if such an
insane value was specified. Let us limit the maximum to 255.
The encryption threads are not doing much useful work.
They are basically only dirtying pages by performing
dummy writes via the redo log. The encryption key rotation
or the in-place addition or removal of encryption
will take place in the page cleaner.
In a quick test on a 20-core CPU (40 threads in total),
the sweet spot on an otherwise idle server seemed to be
innodb_encryption_threads=16 for the test
encryption.encrypt_and_grep. The new limit 255 should be
more than enough for even bigger servers.
This essentially reverts commit b393e2cb0c.
The leak might have been fixed, but because the
DEBUG_SYNC instrumentation for InnoDB purge threads was reverted
in 10.5 commit 5e62b6a5e0
as part of introducing a thread pool, it is easiest to revert
the entire change.
Let us limit the maximum value of the debug parameter
innodb_data_file_size to 256 MiB. It is only being used
in the test innodb.log_data_file_size, and the size
of the system tablespace should never exceed some 70 MiB
in ./mtr. Thus, 256 MiB should be a reasonable limit.
The fact that negative values that are passed to unsigned parameters
wrap around to the maximum value appears to be a regression due to
commit 18ef02b04d
and has been filed as bug MDEV-22219.
If a table is altered using the MDEV-11369/MDEV-15562/MDEV-13134
ALGORITHM=INSTANT, it can force the table to use a non-canonical
format:
* A hidden metadata record at the start of the clustered index
is used to store each column's DEFAULT value. This makes it possible
to add new columns that have default values without rebuilding the table.
* Starting with MDEV-15562 in MariaDB Server 10.4, a BLOB in the
hidden metadata record is used to store column mappings. This makes
it possible to drop or reorder columns without rebuilding the table.
This also makes it possible to add columns to any position or drop
columns from any position in the table without rebuilding the table.
If a column is dropped without rebuilding the table, old records
will contain garbage in that column's former position, and new records
will be written with NULL values, empty strings, or dummy values.
This is generally not a problem. However, there may be cases where
users may want to avoid putting a table into this format.
For example, users may want to ensure that future UPDATE operations
after an ADD COLUMN will be performed in-place, to reduce write
amplification. (Instantly added columns are essentially always
variable-length.) Users might also want to avoid bugs similar to
MDEV-19916, or they may want to be able to export tables to
older versions of the server.
We will introduce the option innodb_instant_alter_column_allowed,
with the following values:
* never (0): Do not allow instant add/drop/reorder,
to maintain format compatibility with MariaDB 10.x and MySQL 5.x.
If the table (or partition) is not in the canonical format, then
any ALTER TABLE (even one that does not involve instant column
operations) will force a table rebuild.
* add_last (1, default in 10.3): Store a hidden metadata record that
allows columns to be appended to the table instantly (MDEV-11369).
In 10.4 or later, if the table (or partition) is not in this format,
then any ALTER TABLE (even one that does not involve column changes)
will force a table rebuild.
Starting with 10.4:
* add_drop_reorder (2, default): Like 'add_last', but allow the
metadata record to store a column map, to support instant
add/drop/reorder of columns (MDEV-15562).
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()
The configuration parameter innodb_scrub_log never really worked, as
reported in MDEV-13019 and MDEV-18370.
Because MDEV-14425 is changing the redo log format, the innodb_scrub_log
feature would have to be adjusted for it. Due to the known problems,
it is easier to remove the feature for now, and to ignore and deprecate
the parameters.
If old log contents should be kept secret, then enabling innodb_encrypt_log
or setting a smaller innodb_log_file_size could help.
Now there can be only one log file instead of several which
logically work as a single file.
Possible names of redo log files: ib_logfile0,
ib_logfile101 (for just created one)
innodb_log_fiels_in_group: value of this variable is not used
by InnoDB. Possible values are still 1..100, to not break upgrade
LOG_FILE_NAME: add constant of value "ib_logfile0"
LOG_FILE_NAME_PREFIX: add constant of value "ib_logfile"
get_log_file_path(): convenience function that returns full
path of a redo log file
SRV_N_LOG_FILES_MAX: removed
srv_n_log_files: we can't remove this for compatibility reasons,
but now server doesn't use this variable
log_sys_t::file::fd: now just one, not std::vector
log_sys_t::log_capacity: removed word 'group'
find_and_check_log_file(): part of logic from huge srv_start()
moved here
recv_sys_t::files: file descriptors of redo log files.
There can be several of those in case we're upgrading
from older MariaDB version.
recv_sys_t::remove_extra_log_files: whether to remove
ib_logfile{1,2,3...} after successfull upgrade.
recv_sys_t::read(): open if needed and read from one
of several log files
recv_sys_t::files_size(): open if needed and return files count
redo_file_sizes_are_correct(): check that redo log files
sizes are equal. Just to log an error for a user.
Corresponding check was moved from srv0start.cc
namespace deprecated: put all deprecated variables here to
prevent usage of it by us, developers
page_zip_compress_write_log_no_data(): Remove.
We no longer write the MLOG_ZIP_PAGE_COMPRESS_NO_DATA record.
Instead, we will write MLOG_ZIP_PAGE_COMPRESS records.
Our benchmarking efforts indicate that the reasons for splitting the
buf_pool in commit c18084f71b
have mostly gone away, possibly as a result of
mysql/mysql-server@ce6109ebfd
or similar work.
Only in one write-heavy benchmark where the working set size is
ten times the buffer pool size, the buf_pool->mutex would be
less contended with 4 buffer pool instances than with 1 instance,
in buf_page_io_complete(). That contention could be alleviated
further by making more use of std::atomic and by splitting
buf_pool_t::mutex further (MDEV-15053).
We will deprecate and ignore the following parameters:
innodb_buffer_pool_instances
innodb_page_cleaners
There will be only one buffer pool and one page cleaner task.
In a number of INFORMATION_SCHEMA views, columns that indicated
the buffer pool instance will be removed:
information_schema.innodb_buffer_page.pool_id
information_schema.innodb_buffer_page_lru.pool_id
information_schema.innodb_buffer_pool_stats.pool_id
information_schema.innodb_cmpmem.buffer_pool_instance
information_schema.innodb_cmpmem_reset.buffer_pool_instance
During native table rebuild or index creation, InnoDB used to skip
redo logging and write MLOG_INDEX_LOAD records to inform crash recovery
and Mariabackup of the gaps in redo log. This is fragile and prohibits
some optimizations, such as skipping the doublewrite buffer for
newly (re)initialized pages (MDEV-19738).
row_merge_write_redo(): Remove. We do not write MLOG_INDEX_LOAD
records any more. Instead, we write full redo log.
FlushObserver: Remove.
fseg_free_page_func(): Remove the parameter log. Redo logging
cannot be disabled.
fil_space_t::redo_skipped_count: Remove.
We cannot remove buf_block_t::skip_flush_check, because PageBulk
will temporarily generate invalid B-tree pages in the buffer pool.
The only change is a change of the version number.
In MySQL 5.6.46, the copyright comments in a number of files were changed
in mysql/mysql-server@f1a006ece7
but there was no functional change to InnoDB code.
This was also reflected by XtraDB. We are not changing the copyright
comments in MariaDB Server for now.
Between MySQL 5.6.46 and 5.6.47, InnoDB was not changed at all.
Actually, we had forgotten to update the InnoDB version number to
5.6.46. With this change, we are updating InnoDB
from 5.6.45 to 5.6.47 and XtraDB from 5.6.45-86.1 to 5.6.46-86.2.
InnoDB RNG maintains global state, causing otherwise unnecessary bus
traffic. Even worse, this is cross-mutex traffic. That is, different
mutexes suffer from contention.
Fixed delay of 4 was verified to give best throughput by OLTP update
index and read-write benchmarks on Intel Broadwell (2/20/40) and
ARM (1/46/46).
This is a backport of ce04790065 from
MariaDB Server 10.3.
Almost all threads have gone
- the "ticking" threads, that sleep a while then do some work)
(srv_monitor_thread, srv_error_monitor_thread, srv_master_thread)
were replaced with timers. Some timers are periodic,
e.g the "master" timer.
- The btr_defragment_thread is also replaced by a timer , which
reschedules it self when current defragment "item" needs throttling
- the buf_resize_thread and buf_dump_threads are substitutes with tasks
Ditto with page cleaner workers.
- purge workers threads are not tasks as well, and purge cleaner
coordinator is a combination of a task and timer.
- All AIO is outsourced to tpool, Innodb just calls thread_pool::submit_io()
and provides the callback.
- The srv_slot_t was removed, and innodb_debug_sync used in purge
is currently not working, and needs reimplementation.
Historically, InnoDB split the redo log into at least 2 files.
MDEV-12061 allowed the minimum to be innodb_log_files_in_group=1,
but it kept the default at innodb_log_files_in_group=2.
Because performance seems to be slightly better with only one log file,
and because implementing an append-only variant of the log would require
a single file, let us define the default to be 1, and have
innodb_log_file_size=96M, to retain the same default total size.
Based on the performance testing that was conducted in MDEV-17492,
the InnoDB adaptive hash index could only help performance in specific,
almost-read-only workloads. It could slow down all kinds of workloads
(especially DROP TABLE, TRUNCATE TABLE, ALTER TABLE, or DROP INDEX
operations), and it can become corrupted, causing crashes (such as
MDEV-18815, MDEV-20203) and possibly data corruption. Furthermore,
the adaptive hash index consumes space from the InnoDB buffer pool,
which could hurt performance when the working set would almost fit
in the buffer pool.
Given all this, it is best to disable the adaptive hash index by default.
To diagnose a hang in slow shutdown (innodb_fast_shutdown=0),
let us introduce a Boolean startup option in debug builds
that will cause the contents of the InnoDB change buffer
to be dumped to the server error log at startup.
