MariaDB async replication SQL thread was stopped for any failure
in applying of replication events and error message logged for the failure
was: "Node has dropped from cluster". The assumption was that event applying
failure is always due to node dropping out.
With optimistic parallel replication, event applying can fail for natural
reasons and applying should be retried to handle the failure. This retry
logic was never exercised because the slave SQL thread was stopped with first
applying failure.
To support optimistic parallel replication retrying logic this commit will
now skip replication slave abort, if node remains in cluster (wsrep_ready==ON)
and replication is configured for optimistic or aggressive retry logic.
During the development of this fix, galera.galera_as_slave_nonprim test showed
some problems. The test was analyzed, and it appears to need some attention.
One excessive sleep command was removed in this commit, but it will need more
fixes still to be fully deterministic. After this commit galera_as_slave_nonprim
is successful, though.
Signed-off-by: Julius Goryavsky <julius.goryavsky@mariadb.com>
The problem was that parallel replication of temporary tables using
statement-based binlogging could overlap the COMMIT in one thread with a DML
or DROP TEMPORARY TABLE in another thread using the same temporary table.
Temporary tables are not safe for concurrent access, so this caused
reference to freed memory and possibly other nastiness.
The fix is to disable the optimisation with overlapping commits of one
transaction with the start of a later transaction, when temporary tables are
in use. Then the following event groups will be blocked from starting until
the one using temporary tables is completed.
This also fixes occasional test failures of rpl.rpl_parallel_temptable seen
in Buildbot.
Signed-off-by: Kristian Nielsen <knielsen@knielsen-hq.org>
When the SQL driver thread goes to wait for room in the parallel slave
worker queue, there was a race where a kill at the right moment could
be ignored and the wait proceed uninterrupted by the kill.
Fix by moving the THD::check_killed() to occur _after_ doing ENTER_COND().
This bug was seen as sporadic failure of the testcase rpl.rpl_parallel
(rpl.rpl_parallel_gco_wait_kill since 10.5), with "Slave stopped with
wrong error code".
Signed-off-by: Kristian Nielsen <knielsen@knielsen-hq.org>
Restore code to make InnoDB choose the second transaction as a deadlock
victim if two transactions deadlock that need to commit in-order for
parallel replication. This code was erroneously removed when VATS was
implemented in InnoDB.
Also add a test case for InnoDB choosing the right deadlock victim.
Also fixes this bug, with testcase that reliably reproduces:
MDEV-28776: rpl.rpl_mark_optimize_tbl_ddl fails with timeout on sync_with_master
Note: This should be null-merged to 10.6, as a different fix is needed
there due to InnoDB locking code changes.
Signed-off-by: Kristian Nielsen <knielsen@knielsen-hq.org>
The largest_started_sub_id needs to be set under LOCK_parallel_entry
together with testing stop_sub_id. However, in-between was the logic for
do_ftwrl_wait(), which temporarily releases the mutex. This could lead to
inconsistent stopping amongst worker threads and lost data.
Fix by moving all the stop-related logic out from unrelated do_gco_wait()
and do_ftwrl_wait() and into its own function do_stop_handling().
Reviewed-by: Andrei Elkin <andrei.elkin@mariadb.com>
Signed-off-by: Kristian Nielsen <knielsen@knielsen-hq.org>
The problem is that when a worker thread is (user) killed in
wait_for_prior_commit, the event group may complete out-of-order since the
wait for prior commit was aborted by the kill.
This fix ensures that event groups will always complete in-order, even
in the error case. This is done in finish_event_group() by doing an
extra wait_for_prior_commit(), if necessary, that ignores kills.
This fix supersedes the fix for MDEV-30780, so the earlier fix for
that is reverted in this patch.
Also fix that an error from wait_for_prior_commit() inside
finish_event_group() would not signal the error to
wakeup_subsequent_commits().
Based on earlier work by Brandon Nesterenko and Andrei Elkin, with
some changes to simplify the semantics of wait_for_prior_commit() and
make the code more robust to future changes.
Reviewed-by: Andrei Elkin <andrei.elkin@mariadb.com>
Signed-off-by: Kristian Nielsen <knielsen@knielsen-hq.org>
The problem was an incorrect unmark_start_commit() in
signal_error_to_sql_driver_thread(). If an event group gets an error, this
unmark could run after the following GCO started, and the subsequent
re-marking could access de-allocated GCO.
The offending unmark_start_commit() looks obviously incorrect, and the fix
is to just remove it. It was introduced in the MDEV-8302 patch, the commit
message of which suggests it was added there solely to satisfy an assertion
in ha_rollback_trans(). So update this assertion instead to not trigger for
event groups that experienced an error (rgi->worker_error). When an error
occurs in an event group, all following event groups are skipped anyway, so
the unmark should never be needed in this case.
Reviewed-by: Andrei Elkin <andrei.elkin@mariadb.com>
Signed-off-by: Kristian Nielsen <knielsen@knielsen-hq.org>
At STOP SLAVE, worker threads will continue applying event groups until the
end of the current GCO before stopping. This is a left-over from when only
conservative mode was available. In optimistic and aggressive mode, often
_all_ queued event will be in the same GCO, and slave stop will be
needlessly delayed.
This patch instead records at STOP SLAVE time the latest (highest sub_id)
event group that has started. Then worker threads will continue to apply
event groups up to that event group, but skip any following. The result is
that each worker thread will complete its currently running event group, and
then the slave will stop.
If the slave is caught up, and STOP SLAVE is run in the middle of an event
group that is already executing in a worker thread, then that event group
will be rolled back and the slave stop immediately, as normal.
Reviewed-by: Andrei Elkin <andrei.elkin@mariadb.com>
Signed-off-by: Kristian Nielsen <knielsen@knielsen-hq.org>
The problem is that a parallel replica would not immediately stop
running/queued transactions when issued STOP SLAVE. That is, it
allowed the current group of transactions to run, and sometimes the
transactions which belong to the next group could be started and run
through commit after STOP SLAVE was issued too, if the last group
had started committing. This would lead to long periods to wait for
all waiting transactions to finish.
This patch updates a parallel replica to try and abort immediately
and roll-back any ongoing transactions. The exception to this is any
transactions which are non-transactional (e.g. those modifying
sequences or non-transactional tables), and any prior transactions,
will be run to completion.
The specifics are as follows:
1. A new stage was added to SHOW PROCESSLIST output for the SQL
Thread when it is waiting for a replica thread to either rollback or
finish its transaction before stopping. This stage presents as
“Waiting for worker thread to stop”
2. Worker threads which error or are killed no longer perform GCO
cleanup if there is a concurrently running prior transaction. This
is because a worker thread scheduled to run in a future GCO could be
killed and incorrectly perform cleanup of the active GCO.
3. Refined cases when the FL_TRANSACTIONAL flag is added to GTID
binlog events to disallow adding it to transactions which modify
both transactional and non-transactional engines when the binlogging
configuration allow the modifications to exist in the same event,
i.e. when using binlog_direct_non_trans_update == 0 and
binlog_format == statement.
4. A few existing MTR tests relied on the completion of certain
transactions after issuing STOP SLAVE, and were re-recorded
(potentially with added synchronizations) under the new rollback
behavior.
Reviewed By
===========
Andrei Elkin <andrei.elkin@mariadb.com>
The problem was that mutex_init() was called after the worker was
put into the domain_hash, which allowed other threads to access it
before mutex was initialized.
When using binlog_row_image=FULL with sequence table inserts, a
replica can deadlock because it treats full inserts in a sequence as DDL
statements by getting an exclusive lock on the sequence table. It
has been observed that with parallel replication, this exclusive
lock on the sequence table can lead to a deadlock where one
transaction has the exclusive lock and is waiting on a prior
transaction to commit, whereas this prior transaction is waiting on
the MDL lock.
This fix for this is on the master side, to raise FL_DDL
flag on the GTID of a full binlog_row_image write of a sequence table.
This forces the slave to execute the statement serially so a deadlock
cannot happen.
A test verifies the deadlock also to prove it happen on the OLD (pre-fixes)
slave.
OLD (buggy master) -replication-> NEW (fixed slave) is provided.
As the pre-fixes master's full row-image may represent both
SELECT NEXT VALUE and INSERT, the parallel slave pessimistically
waits for the prior transaction to have committed before to take on the
critical part of the second (like INSERT in the test) event execution.
The waiting exploits a parallel slave's retry mechanism which is
controlled by `@@global.slave_transaction_retries`.
Note that in order to avoid any persistent 'Deadlock found' 2013 error
in OLD -> NEW, `slave_transaction_retries` may need to be set to a
higher than the default value.
START-SLAVE is an effective work-around if this still happens.
The error was seen by a number of mtr tests being caused
by overdue initialization of rpl_parallel::LOCK_parallel_entry.
Specifically, SHOW-SLAVE-STATUS might find in
rpl_parallel::workers_idle() a gtid domain hash entry
already inserted whose mutex had not done
mysql_mutex_init().
Fixed with swapping the mutex init and the its entry's stack insertion.
Tested with a generous number of `mtr --repeat` of a few of the reported
to fail tests, incl rpl.parallel_backup.
The hang could be seen as show slave status displaying an error like
Last_Error: Could not execute Write_rows_v1
along with
Slave_SQL_Running: Yes
accompanied with one of the replication threads in show-processlist
characteristically having status like
2394 | system user | | NULL | Slave_worker | 50852| closing tables
It turns out that closing tables worker got entrapped in endless looping
in mark_start_commit_inner() across already garbage-collected gco items.
The reclaimed gco links are explained with actually possible
out-of-order groups of events termination due to the Last_Error.
This patch reinforces the correct ordering to perform
finish_event_group's cleanup actions, incl unlinking gco:s
from the active list.
Problem
========
On a parallel, delayed replica, Seconds_Behind_Master will not be
calculated until after MASTER_DELAY seconds have passed and the
event has finished executing, resulting in potentially very large
values of Seconds_Behind_Master (which could be much larger than the
MASTER_DELAY parameter) for the entire duration the event is
delayed. This contradicts the documented MASTER_DELAY behavior,
which specifies how many seconds to withhold replicated events from
execution.
Solution
========
After a parallel replica idles, the first event after idling should
immediately update last_master_timestamp with the time that it began
execution on the primary.
Reviewed By
===========
Andrei Elkin <andrei.elkin@mariadb.com>
There are separate flags DBUG_OFF for disabling the DBUG facility
and ENABLED_DEBUG_SYNC for enabling the DEBUG_SYNC facility.
Let us allow debug builds without DEBUG_SYNC.
Note: For CMAKE_BUILD_TYPE=Debug, CMakeLists.txt will continue to
define ENABLED_DEBUG_SYNC.
Problem:- When we issue FTWRL with shutdown in parallel, there is race between
FTWRL and shutdown. Shutdown might destroy the mutex (pool->LOCK_rpl_thread_pool)
before FTWRL can lock it. So we can get crash on FTWRL thread
Solution:- mysql_mutex_destroy(pool->LOCK_rpl_thread_pool) should wait for
FTWRL thread to complete its work , and then destroy.
So slave_prepare_for_shutdown will just deactivate the pool, and mutex is destroyed
later in end_slave()
Problem:
========
Auto purge of relaylogs stops when relay-log-file is
'slave-relay-log.999999' and slave_parallel_threads is enabled.
Analysis:
=========
The problem is that in Relay_log_info::inc_group_relay_log_pos() function,
when two log names are compared via strcmp() function, it gives correct
result, when log name sequence numbers are of same digits(6 digits), But
when the number goes to 7 digits, a 999999 compares greater than
1000000, which is wrong, hence the bug.
Fix:
====
Extract the numeric extension part of the file name, convert it into
unsigned long and compare.
Thanks to David Zhao for the contribution.
Problem:- rpl_parallel2 was failing non-deterministically
Analysis:-
When FLUSH TABLES WITH READ LOCK is executed, it will allow all worker
threads to complete their ongoing transactions and then it will pause them.
At this state FTWRL will proceed to acquire global read lock. FTWRL first
blocks threads from starting new commits, then upgrades the lock to block
commit of existing transactions.
Step1:
FLUSH TABLES WITH READ LOCK - Blocks new commits
Step2:
* STOP SLAVE command enables 'force_abort=1' which unblocks workers,
they continue to execute events.
* T1: Waits in 'record_gtid' call to update 'gtid_slave_pos' table with
its current GTID, but it is blocked becuase of Step1.
* T2: Holds COMMIT lock and waits for T1 to commit.
Step3:
FLUSH TABLES WITH READ LOCK - Waiting to get BLOCK_COMMIT.
This results in deadlock. When STOP SLAVE command allows paused workers to
proceed, workers should skip the execution of all further events, similar
to 'conservative' parallel mode.
Solution:-
We will assign 1 to skip_event_group when we are aborted in do_ftwrl_wait.
rpl_parallel_entry->pause_sub_id is only reset when force_abort is off in
rpl_pause_after_ftwrl.
Problem:- rpl_parallel2 was failing non-deterministically
Analysis:-
When FLUSH TABLES WITH READ LOCK is executed, it will allow all worker
threads to complete their ongoing transactions and then it will pause them.
At this state FTWRL will proceed to acquire global read lock. FTWRL first
blocks threads from starting new commits, then upgrades the lock to block
commit of existing transactions.
Step1:
FLUSH TABLES WITH READ LOCK - Blocks new commits
Step2:
* STOP SLAVE command enables 'force_abort=1' which unblocks workers,
they continue to execute events.
* T1: Waits in 'record_gtid' call to update 'gtid_slave_pos' table with
its current GTID, but it is blocked becuase of Step1.
* T2: Holds COMMIT lock and waits for T1 to commit.
Step3:
FLUSH TABLES WITH READ LOCK - Waiting to get BLOCK_COMMIT.
This results in deadlock. When STOP SLAVE command allows paused workers to
proceed, workers should skip the execution of all further events, similar
to 'conservative' parallel mode.
Solution:-
We will assign 1 to skip_event_group when we are aborted in do_ftwrl_wait.
rpl_parallel_entry->pause_sub_id is only reset when force_abort is off in
rpl_pause_after_ftwrl.
The issue was:
T1, a parallel slave worker thread, is waiting for another worker thread to
commit. While waiting, it has the MDL_BACKUP_COMMIT lock.
T2, working for mariabackup, is doing BACKUP STAGE BLOCK_COMMIT and blocks
all commits.
This causes a deadlock as the thread T1 is waiting for can't commit.
Fixed by moving locking of MDL_BACKUP_COMMIT from ha_commit_trans() to
commit_one_phase_2()
Other things:
- Added a new argument to ha_comit_one_phase() to signal if the
transaction was a write transaction.
- Ensured that ha_maria::implicit_commit() is always called under
MDL_BACKUP_COMMIT. This code is not needed in 10.5
- Ensure that MDL_Request values 'type' and 'ticket' are always
initialized. This makes it easier to check the state of the MDL_Request.
- Moved thd->store_globals() earlier in handle_rpl_parallel_thread() as
thd->init_for_queries() could use a MDL that could crash if store_globals
where not called.
- Don't call ha_enable_transactions() in THD::init_for_queries() as this
is both slow (uses MDL locks) and not needed.
Problem:- When we issue FTWRL with shutdown in parallel, there is race between
FTWRL and shutdown. Shutdown might destroy the mutex (pool->LOCK_rpl_thread_pool)
before FTWRL can lock it. So we can get crash on FTWRL thread
Solution:- mysql_mutex_destroy(pool->LOCK_rpl_thread_pool) should wait for
FTWRL thread to complete its work , and then destroy.
So slave_prepare_for_shutdown will just deactivate the pool, and mutex is destroyed
later in end_slave()
The immediate bug was caused by a failure to recognize a correct
position to stop the slave applier run in optimistic parallel mode.
There were the following set of issues that the analysis unveil.
1 incorrect estimate for the event binlog position passed to
is_until_satisfied
2 wait for workers to complete by the driver thread did not account non-group events
that could be left unprocessed and thus to mix up the last executed
binlog group's file and position:
the file remained old and the position related to the new rotated file
3 incorrect 'slave reached file:pos' by the parallel slave report in the error log
4 relay log UNTIL missed out the parallel slave branch in
is_until_satisfied.
The patch addresses all of them to simplify logics of log change
notification in either the master and relay-log until case.
P.1 is addressed with passing the event into is_until_satisfied()
for proper analisis by the function.
P.2 is fixed by changes in handle_queued_pos_update().
P.4 required removing relay-log change notification by workers.
Instead the driver thread updates the notion of the current relay-log
fully itself with aid of introduced
bool Relay_log_info::until_relay_log_names_defer.
An extra print out of the requested until file:pos is arranged
with --log-warning=3.
The immediate bug was caused by a failure to recognize a correct
position to stop the slave applier run in optimistic parallel mode.
There were the following set of issues that the analysis unveil.
1 incorrect estimate for the event binlog position passed to
is_until_satisfied
2 wait for workers to complete by the driver thread did not account non-group events
that could be left unprocessed and thus to mix up the last executed
binlog group's file and position:
the file remained old and the position related to the new rotated file
3 incorrect 'slave reached file:pos' by the parallel slave report in the error log
4 relay log UNTIL missed out the parallel slave branch in
is_until_satisfied.
The patch addresses all of them to simplify logics of log change
notification in either the master and relay-log until case.
P.1 is addressed with passing the event into is_until_satisfied()
for proper analisis by the function.
P.2 is fixed by changes in handle_queued_pos_update().
P.4 required removing relay-log change notification by workers.
Instead the driver thread updates the notion of the current relay-log
fully itself with aid of introduced
bool Relay_log_info::until_relay_log_names_defer.
An extra print out of the requested until file:pos is arranged
with --log-warning=3.
