Before doing mark_start_commit(), check that there is no pending deadlock
kill. If there is a pending kill, we won't commit (we will abort, roll back,
and retry). Then we should not mark the commit as started, since that could
potentially make the following GCO start too early, before we completed the
commit after the retry.
This condition could trigger in some corner cases, where InnoDB would take
temporarily table/row locks that are released again immediately, not held
until the transaction commits. This happens with dict_stats updates and
possibly auto-increment locks.
Such locks can be passed to thd_rpl_deadlock_check() and cause a deadlock
kill to be scheduled in the background. But since the blocking locks are
held only temporarily, they can be released before the background kill
happens. This way, the kill can be delayed until after mark_start_commit()
has been called. Thus we need to check the synchronous indication
rgi->killed_for_retry, not just the asynchroneous thd->killed.
Signed-off-by: Kristian Nielsen <knielsen@knielsen-hq.org>
Similar to #2480.
567b681 introduced safe_strcpy() to minimize the use of C with
potentially unsafe memory overflow with strcpy() whose use is
discouraged.
Replace instances of strcpy() with safe_strcpy() where possible, limited
here to files in the `sql/` directory.
All new code of the whole pull request, including one or several files
that are either new files or modified ones, are contributed under the
BSD-new license. I am contributing on behalf of my employer
Amazon Web Services, Inc.
Clear any pending deadlock kill after completing XA PREPARE, and before
updating the mysql.gtid_slave_pos table in a separate transaction.
Reviewed-by: Andrei Elkin <andrei.elkin@mariadb.com>
Signed-off-by: Kristian Nielsen <knielsen@knielsen-hq.org>
Keep track of each recently active XID, recording which worker it was queued
on. If an XID might still be active, choose the same worker to queue event
groups that refer to the same XID to avoid conflicts.
Otherwise, schedule the XID freely in the next round-robin slot.
This way, XA PREPARE can normally be scheduled without restrictions (unless
duplicate XID transactions come close together). This improves scheduling
and parallelism over the old method, where the worker thread to schedule XA
PREPARE on was fixed based on a hash value of the XID.
XA COMMIT will normally be scheduled on the same worker as XA PREPARE, but
can be a different one if the XA PREPARE is far back in the event history.
Testcase and code for trimming dynamic array due to Andrei.
Reviewed-by: Andrei Elkin <andrei.elkin@mariadb.com>
Signed-off-by: Kristian Nielsen <knielsen@knielsen-hq.org>
This is a preparatory patch to facilitate the next commit to improve
the scheduling of XA transactions in parallel replication.
When choosing the scheduling bucket for the next event group in
rpl_parallel_entry::choose_thread(), use an explicit FIFO for the
round-robin selection instead of a simple cyclic counter i := (i+1) % N.
This allows to schedule XA COMMIT/ROLLBACK dependencies explicitly without
changing the round-robin scheduling of other event groups.
Reviewed-by: Andrei Elkin <andrei.elkin@mariadb.com>
Signed-off-by: Kristian Nielsen <knielsen@knielsen-hq.org>
When rolling back and retrying a transaction in parallel replication, don't
release the domain ownership (for --gtid-ignore-duplicates) as part of the
rollback. Otherwise another master connection could grab the ownership and
double-apply the transaction in parallel with the retry.
Reviewed-by: Brandon Nesterenko <brandon.nesterenko@mariadb.com>
Signed-off-by: Kristian Nielsen <knielsen@knielsen-hq.org>
This will makes it easier to find out what replication workers are
doing and what they are waiting for.
Things changed in processlist:
- Slave_SQL time was not consistent. Now time for state "Slave has
read all relay log; waiting for more updates" shows how long it has
waited for getting the next event.
- Slave_worker threads did often show "Closing tables" for a long
time. Now the state is reverted to the previous state after
"Closing tables" is done.
- Commit and Rollback states where not shown for replication (and some
other threads). Now Commit and Rollback states are always shown and
the state is reverted to previous state when the Commit/Rollback
have finished.
Code changes:
- Added thd->set_time_for_next_stage() for parallel replication when
when starting to wait for prior transactions to commit, group commit,
and FTWRL and for free space in thread pool.
Before we reset the time only after the above events.
- Moved THD_STAGE_INFO(stage_rollback) and THD_STAGE_INFO(stage_commit)
from sql_parse.cc to transaction.cc to ensure this is done for
all commits and not only 'normal connection queries'.
Test case changes:
- close_thread_tables() reverting stage to previous stage caused the
counter in performance_schema to be increased. In many case it is
the 'sql/starting' stage that was effected.
- We only change to "Commit" stage if there is a need for a commit.
This caused some "Commit" stages to disapper from perfschema reports.
TODO in 11.#:
- Slave_IO always showes "Waiting for master to send event" and the time is
from SLAVE START. We should in 11.# change this to be the time since
reading the last event.
The previous patch for MDEV-10653 changes the rpl_parallel::workers_idle()
function to use Relay_log_info::last_inuse_relaylog to check for idle
workers. But the code was missing a NULL check. Also, there was one place
during SQL slave thread start which was missing mutex synchronisation when
updating inuse_relaylog.
Signed-off-by: Kristian Nielsen <knielsen@knielsen-hq.org>
The error-injection inject_mdev8031 simulates a deadlock kill in a specific
place, by setting killed_for_retry to RETRY_KILL_KILLED directly. If a real
deadlock kill triggers at the same time, it is possible for the thread to
complete its transaction retry and set rgi_slave to NULL before the real
readlock kill can complete in the background. This will cause a segfault
due to null-pointer access.
Fix by changing the error injection to do a real background deadlock kill,
which ensures that the thread will wait for any pending background kills to
complete.
Signed-off-by: Kristian Nielsen <knielsen@knielsen-hq.org>
AKA rpl.rpl_parallel, binlog_encryption.rpl_parallel fails in
buildbot with timeout in include
A replication parallel worker thread can deadlock with another
connection running SHOW SLAVE STATUS. That is, if the replication
worker thread is in do_gco_wait() and is killed, it will already
hold the LOCK_parallel_entry, and during error reporting, try to
grab the err_lock. SHOW SLAVE STATUS, however, grabs these locks in
reverse order. It will initially grab the err_lock, and then try to
grab LOCK_parallel_entry. This leads to a deadlock when both threads
have grabbed their first lock without the second.
This patch implements the MDEV-31894 proposed fix to optimize the
workers_idle() check to compare the last in-use relay log’s
queued_count==dequeued_count for idleness. This removes the need for
workers_idle() to grab LOCK_parallel_entry, as these values are
atomically updated.
Huge thanks to Kristian Nielsen for diagnosing the problem!
Reviewed By:
============
Kristian Nielsen <knielsen@knielsen-hq.org>
Andrei Elkin <andrei.elkin@mariadb.com>
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
Reviewed-by: Marko Mäkelä <marko.makela@mariadb.com>
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.
…with: Test assertion failed
Problem:
=======
Assertion text: 'Value returned by SSS and PS table for Last_Error_Number
should be same.'
Assertion condition: '"1146" = "0"'
Assertion condition, interpolated: '"1146" = "0"'
Assertion result: '0'
Analysis:
========
In parallel replication when slave is started the worker pool gets
activated and it gets cleared when slave stops. Each time the worker pool
gets activated a backup worker pool also gets created to store worker
specific perforance schema information in case of errors. On error, all
relevant information is copied from rpl_parallel_thread to rli and it gets
cleared from thread. Then server waits for all workers to complete their
work, during this stage performance schema table specific worker info is
stored into the backup pool and finally the actual pool gets cleared. If
users query the performance schema table to know the status of workers the
information from backup pool will be used. The test simulates
ER_NO_SUCH_TABLE error and verifies the worker information in pfs table.
Test works fine if execution occurs in following order.
Step 1. Error occurred 'worker information is copied to backup pool'.
Step 2. handle_slave_sql invokes 'rpl_parallel_resize_pool_if_no_slaves' to
deactivate worker pool, it marks the pool->count=0
Step 3. PFS table is queried, since actual pool is deactivated backup pool
information is read.
If the Step 3 happens prior to Step2 the pool is yet to be deactivated and
the actual pool is read, which doesn't have any error details as they were
cleared. Hence test ocasionally fails.
Fix:
===
Upon error mark the back pool as being active so that if PFS table is
quried since the backup pool is flagged as valid its information will be
read, in case it is not flagged regular pool will be read.
This work is one of the last pieces created by the late Sujatha Sivakumar.
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.
