Problem:
========
When the mysql.gtid_slave_pos table uses the InnoDB engine, and
mysqld starts, it reads the table and begins a transaction. After
reading the value, it should end the transaction and release all
associated locks. The bug reported in DBAAS-7828 shows that when
autocommit is off, the locks are not released, resulting in
indefinite hangs on future attempts to change gtid_slave_pos. In
particular, the transaction was not properly finalized because
thd->server_status was not updated to reflect the end of the
transaction.
Solution:
========
This patch updates the code to properly commit the transaction after
reading gtid_slave_pos during mysqld start-up.
Reviewed By:
============
Andrei Elkin <andrei.elkin@mariadb.com>
No longer a MySQL server, "his" is the wrong pronoun
for a server.
Thanks Michael Newton for highlighting these problems
Also changed slave -> replica.
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.
The reason for the failure is that
thd->mdl_context.release_transactional_locks()
was called after commit & rollback even in cases where the current
transaction is still active.
For 10.2, 10.3 and 10.4 the fix is simple:
- Replace all calls to thd->mdl_context.release_transactional_locks() with
thd->release_transactional_locks(). The thd function will only call
the mdl_context function if there are no active transactional locks.
In 10.6 we will better fix where we will change the return value for
some trans_xxx() functions to indicate if transaction did close the
transaction or not. This will avoid the need of the indirect call.
Other things:
- trans_xa_commit() and trans_xa_rollback() will automatically
call release_transactional_locks() if the transaction is closed.
- We can't do that for the other functions as the caller of many of these
are doing additional work (like close_thread_tables) before calling
release_transactional_locks().
- Added missing abort_result_set() and missing DBUG_RETURN in
select_create::send_eof()
- Fixed wrong indentation in injector::transaction::commit()
Analysis:
========
Writes to 'rli->log_space_total' needs to be synchronized, otherwise both
SQL_THREAD and IO_THREAD can try to modify the variable simultaneously
resulting in incorrect rli->log_space_total. In the current test scenario
SQL_THREAD is trying to decrement 'rli->log_space_total' in 'purge_first_log'
and IO_THREAD is trying to increment the 'rli->log_space_total' in
'queue_event' simultaneously. Hence test occasionally fails with result
mismatch.
Fix:
===
Convert 'rli->log_space_total' variable to atomic type.
Problem:
========
Relay_log_info::flush reports following MSAN issue.
==17820==WARNING: MemorySanitizer: use-of-uninitialized-value is reported
#5 0x00005584f0981441 in my_write (Filedes=22,
Buffer=0x72500003e818 "5\n./slave-relay-bin.000003\n21385\n
master-bin.000001\n21643\n0\n", '\245' <repeats 141 times>..., Count=118,
MyFlags=532) at /home/sujatha/bug_repo/test-10.5-msan/mysys/my_write.c:49
Analysis:
=========
In parallel replication at the end of each statement execution the worker execution
status is updated in 'relay-log.info' file. When two workers try to flush
the status at the same time, since the write to cache is not serialized both
workers write to the same address simultaneously and increment the
length twice. Because of this the length of buffer is more than actual data.
When flush code tries to read the buffer beyond valid data length MSAN
reports uninitialized values error.
Fix:
===
Serialize the relay log flush operation using "rli->data_lock".
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.
This patch changes how old rows in mysql.gtid_slave_pos* tables are deleted.
Instead of doing it as part of every replicated transaction in
record_gtid(), it is done periodically (every @@gtid_cleanup_batch_size
transaction) in the slave background thread.
This removes the deletion step from the replication process in SQL or worker
threads, which could speed up replication with many small transactions. It
also decreases contention on the global mutex LOCK_slave_state. And it
simplifies the logic, eg. when a replicated transaction fails after having
deleted old rows.
With this patch, the deletion of old GTID rows happens asynchroneously and
slightly non-deterministic. Thus the number of old rows in
mysql.gtid_slave_pos can temporarily exceed @@gtid_cleanup_batch_size. But
all old rows will be deleted eventually after sufficiently many new GTIDs
have been replicated.
This would happen especially in optimistic parallel replication, where there
is a good chance that a transaction will be rolled back (due to conflicts)
after it has executed record_gtid(). If the transaction did any deletions of
old rows as part of record_gtid(), those deletions will be undone as well.
And the code did not properly ensure that the deletions would be re-tried.
This patch makes record_gtid() remember the list of deletions done as part
of a transaction. Then in rpl_slave_state::update() when the changes have
been committed, we discard the list. However, in case of error and rollback,
in cleanup_context() we will instead put the list back into
rpl_global_gtid_slave_state so that the deletions will be re-tried later.
Probably fixes part of the cause of MDEV-12147 as well.
Signed-off-by: Kristian Nielsen <knielsen@knielsen-hq.org>
Replicated transaction extra gtid statement on slave failed to specify
an engine gtid_slave_pos name correctly. In case lower-case-table-names > 0
the InnoDB table name was generated to reproduce the lower-case-table-names=0 version
which is of mixed cases.
In rpl.rpl_mdev12179 test run this triggered a failure to DROP table which
was due to the innodb table handle was not closed:
InnoDB: Waited XYZ seconds for ref-count on table: `mysql`.`gtid_slave_pos_innodb`
on windows.
The closing issue was caused by having the table registered twice in the table cache,
for its lower- and mixed- case name versions. The DROP-table handler closed only
only one of the cache item to leave the 2nd one active.
(On Linux a failure occurs earlier at attempt to open an expected lower-cased table:
Last_Error: Error during XID COMMIT: failed to update GTID state in mysql.gtid_slave_pos: 1146: Table 'mysql.gtid_slave_pos_InnoDB' doesn't exist
but the table's name as the message shows is not in the right case).
Fixed with consulting lower-case-table-names when the engine gtid-slave-pos table
is created.
Note the lower-case-table-names=a-value created table will not recognized when next
the lower case option changes to a different value.
In 10.4 a follow-up patch is going to lowercase gtid-slave-pos autocreated table
at once at their origination, and a warning is issued in the 10.3 current patch.
This was done in, among other things:
- thd->db and thd->db_length
- TABLE_LIST tablename, db, alias and schema_name
- Audit plugin database name
- lex->db
- All db and table names in Alter_table_ctx
- st_select_lex db
Other things:
- Changed a lot of functions to take const LEX_CSTRING* as argument
for db, table_name and alias. See init_one_table() as an example.
- Changed some function arguments from LEX_CSTRING to const LEX_CSTRING
- Changed some lists from LEX_STRING to LEX_CSTRING
- threads_mysql.result changed because process list_db wasn't always
correctly updated
- New append_identifier() function that takes LEX_CSTRING* as arguments
- Added new element tmp_buff to Alter_table_ctx to separate temp name
handling from temporary space
- Ensure we store the length after my_casedn_str() of table/db names
- Removed not used version of rename_table_in_stat_tables()
- Changed Natural_join_column::table_name and db_name() to never return
NULL (used for print)
- thd->get_db() now returns db as a printable string (thd->db.str or "")
and specifically the ack receiving functionality.
Semisync is turned to be static instead of plugin so its functions
are invoked at the same points as RUN_HOOKS.
The RUN_HOOKS and the observer interface remain to be removed by later
patch.
Todo:
React on killed status by repl_semisync_master.wait_after_sync(). Currently
Repl_semi_sync_master::commit_trx does not check the killed status.
There were few bugfixes found that are present in mysql and its unclear
whether/how they are covered. Those include:
Bug#15985893: GTID SKIPPED EVENTS ON MASTER CAUSE SEMI SYNC TIME-OUTS
Bug#17932935 CALLING IS_SEMI_SYNC_SLAVE() IN EACH FUNCTION CALL
HAS BAD PERFORMANCE
Bug#20574628: SEMI-SYNC REPLICATION PERFORMANCE DEGRADES WITH A HIGH NUMBER OF THREADS
Part of MDEV-13073 AliSQL Optimize performance of semisync
The idea it to use a dedicated lock detecting if there is new data in
the master's binary log instead of the overused LOCK_log.
Changes:
- Use dedicated COND variables for the relay and binary log signaling.
This was needed as we where the old 'update_cond' variable was used
with different mutex's, which could cause deadlocks.
- Relay log uses now COND_relay_log_updated and LOCK_log
- Binary log uses now COND_bin_log_updated and LOCK_binlog_end_pos
- Renamed signal_cnt to relay_signal_cnt (as we now have two signals)
- Added some missing error handling in MYSQL_BIN_LOG::new_file_impl()
- Reformatted some comments with old style
- Renamed m_key_LOCK_binlog_end_pos to key_LOCK_binlog_end_pos
- Changed 'signal_update()' to update_binlog_end_pos() which works for
both relay and binary log
