When a transaction fails in parallel replication, it should signal the error
to any following transactions doing wait_for_prior_commit() on it. But the
code for this was incorrect, and would not correctly remember a prior error
when sending the signal. This caused corruption when slave stopped due to an
error.
Fix by remembering the error code when we first get an error, and passing the
saved error code to wakeup_subsequent_commits().
Thanks to nanyi607rao who reported this bug on
maria-developers@lists.launchpad.net and analysed the root cause.
Before, the arrival of same GTID twice in multi-source replication
would cause double-apply or in gtid strict mode an error.
Keep the behaviour, but add an option --gtid-ignore-duplicates which
allows to correctly handle duplicates, ignoring all but the first.
This relies on the user ensuring correct configuration so that
sequence numbers are strictly increasing within each replication
domain; then duplicates can be detected simply by comparing the
sequence numbers against what is already applied.
Only one master connection (but possibly multiple parallel worker
threads within that connection) is allowed to apply events within
one replication domain at a time; any other connection that
receives a GTID in the same domain either discards it (if it is
already applied) or waits for the other connection to not have
any events to apply.
Intermediate patch, as proof-of-concept for testing. The main limitation
is that currently it is only implemented for parallel replication,
@@slave_parallel_threads > 0.
With parallel replication, there can be any number of events queued on
in-memory lists in the worker threads.
For normal STOP SLAVE, we want to skip executing any remaining events on those
lists and stop as quickly as possible.
However, for START SLAVE UNTIL, when the UNTIL position is reached in the SQL
driver thread, we must _not_ stop until all already queued events for the
workers have been executed - otherwise we would stop too early, before the
actual UNTIL position had been completely reached.
The code did not handle UNTIL correctly, stopping too early due to not
executing the queued events to completion. Fix this, and also implement that
an explicit STOP SLAVE in the middle (when the SQL driver thread has reached
the UNTIL position but the workers have not) _will_ cause an immediate stop.
Clean up and improve the parallel implementation code, mainly related to
scheduling of work to threads and handling of stop and errors.
Fix a lot of bugs in various corner cases that could lead to crashes or
corruption.
Fix that a single replication domain could easily grab all worker threads and
stall all other domains; now a configuration variable
--slave-domain-parallel-threads allows to limit the number of
workers.
Allow next event group to start as soon as previous group begins the commit
phase (as opposed to when it ends it); this allows multiple event groups on
the slave to participate in group commit, even when no other opportunities for
parallelism are available.
Various fixes:
- Fix some races in the rpl.rpl_parallel test case.
- Fix an old incorrect assertion in Log_event iocache read.
- Fix repeated malloc/free of wait_for_commit and rpl_group_info objects.
- Simplify wait_for_commit wakeup logic.
- Fix one case in queue_for_group_commit() where killing one thread would
fail to correctly signal the error to the next, causing loss of the
transaction after slave restart.
- Fix leaking of pthreads (and their allocated stack) due to missing
PTHREAD_CREATE_DETACHED attribute.
- Fix how one batch of group-committed transactions wait for the previous
batch before starting to execute themselves. The old code had a very
complex scheduling where the first transaction was handled differently,
with subtle bugs in corner cases. Now each event group is always scheduled
for a new worker (in a round-robin fashion amongst available workers).
Keep a count of how many transactions have started to commit, and wait for
that counter to reach the appropriate value.
- Fix slave stop to wait for all workers to actually complete processing;
before, the wait was for update of last_committed_sub_id, which happens a
bit earlier, and could leave worker threads potentially accessing bits of
the replication state that is no longer valid after slave stop.
- Fix a couple of places where the test suite would kill a thread waiting
inside enter_cond() in connection with debug_sync; debug_sync + kill can
crash in rare cases due to a race with mysys_var_current_mutex in this
case.
- Fix some corner cases where we had enter_cond() but no exit_cond().
- Fix that we could get failure in wait_for_prior_commit() but forget to flag
the error with my_error().
- Fix slave stop (both for normal stop and stop due to error). Now, at stop
we pick a specific safe point (in terms of event groups executed) and make
sure that all event groups before that point are executed to completion,
and that no event group after start executing; this ensures a safe place to
restart replication, even for non-transactional stuff/DDL. In error stop,
make sure that all prior event groups are allowed to execute to completion,
and that any later event groups that have started are rolled back, if
possible. The old code could leave eg. T1 and T3 committed but T2 not, or
it could even leave half a transaction not rolled back in some random
worker, which would cause big problems when that worker was later reused
after slave restart.
- Fix the accounting of amount of events queued for one worker. Before, the
amount was reduced immediately as soon as the events were dequeued (which
happens all at once); this allowed twice the amount of events to be queued
in memory for each single worker, which is not what users would expect.
- Fix that an error set during execution of one event was sometimes not
cleared before executing the next, causing problems with the error
reporting.
- Fix incorrect handling of thd->killed in worker threads.
MDEV-4984: Implement MASTER_GTID_WAIT() and @@LAST_GTID.
MDEV-4726: Race in mysql-test/suite/rpl/t/rpl_gtid_stop_start.test
MDEV-5636: Deadlock in RESET MASTER
MASTER_GTID_WAIT() is similar to MASTER_POS_WAIT(), but works with a
GTID position rather than an old-style filename/offset.
@@LAST_GTID gives the GTID assigned to the last transaction written
into the binlog.
Together, the two can be used by applications to obtain the GTID of
an update on the master, and then do a MASTER_GTID_WAIT() for that
position on any read slave where it is important to get results that
are caught up with the master at least to the point of the update.
The implementation of MASTER_GTID_WAIT() is implemented in a way
that tries to minimise the performance impact on the SQL threads,
even in the presense of many waiters on single GTID positions (as
from @@LAST_GTID).
- CREATE TABLE is by default executed on the slave as CREATE OR REPLACE
- DROP TABLE is by default executed on the slave as DROP TABLE IF NOT EXISTS
This means that a slave will by default continue even if we try to create
a table that existed on the slave (the table will be deleted and re-created) or
if we try to drop a table that didn't exist on the slave.
This should be safe as instead of having the slave stop because of an inconsistency between
master and slave, it will fix the inconsistency.
Those that would prefer to get a stopped slave instead for the above cases can set slave_ddl_exec_mode to STRICT.
- Ensure that a CREATE OR REPLACE TABLE which dropped a table is replicated
- DROP TABLE that generated an error on master is handled as an identical DROP TABLE on the slave (IF NOT EXISTS is not added in this case)
- Added slave_ddl_exec_mode variable to decide how DDL's are replicated
New logic for handling BEGIN GTID ... COMMIT from the binary log:
- When we find a BEGIN GTID, we start a transaction and set OPTION_GTID_BEGIN
- When we find COMMIT, we reset OPTION_GTID_BEGIN and execute the normal COMMIT code.
- While OPTION_GTID_BEGIN is set:
- We don't generate implict commits before or after statements
- All tables are regarded as transactional tables in the binary log (to ensure things are executed exactly as on the master)
- We reset OPTION_GTID_BEGIN also on rollback
This will help ensuring that we don't get any sporadic commits (and thus new GTID's) on the slave and will help keep the GTID's between master and slave in sync.
mysql-test/extra/rpl_tests/rpl_log.test:
Added testing of mode slave_ddl_exec_mode=STRICT
mysql-test/r/mysqld--help.result:
New help messages
mysql-test/suite/rpl/r/create_or_replace_mix.result:
Testing of CREATE OR REPLACE TABLE with replication
mysql-test/suite/rpl/r/create_or_replace_row.result:
Testing of CREATE OR REPLACE TABLE with replication
mysql-test/suite/rpl/r/create_or_replace_statement.result:
Testing replication of create or replace
mysql-test/suite/rpl/r/rpl_gtid_startpos.result:
Test must be run in slave_ddl_exec_mode=STRICT as part of the test depends on that DROP TABLE should fail on slave.
mysql-test/suite/rpl/r/rpl_row_log.result:
Updated result
mysql-test/suite/rpl/r/rpl_row_log_innodb.result:
Updated result
mysql-test/suite/rpl/r/rpl_row_show_relaylog_events.result:
Updated result
mysql-test/suite/rpl/r/rpl_stm_log.result:
Updated result
mysql-test/suite/rpl/r/rpl_stm_mix_show_relaylog_events.result:
Updated result
mysql-test/suite/rpl/r/rpl_temp_table_mix_row.result:
Updated result
mysql-test/suite/rpl/t/create_or_replace.inc:
Testing of CREATE OR REPLACE TABLE with replication
mysql-test/suite/rpl/t/create_or_replace_mix.cnf:
Testing of CREATE OR REPLACE TABLE with replication
mysql-test/suite/rpl/t/create_or_replace_mix.test:
Testing of CREATE OR REPLACE TABLE with replication
mysql-test/suite/rpl/t/create_or_replace_row.cnf:
Testing of CREATE OR REPLACE TABLE with replication
mysql-test/suite/rpl/t/create_or_replace_row.test:
Testing of CREATE OR REPLACE TABLE with replication
mysql-test/suite/rpl/t/create_or_replace_statement.cnf:
Testing of CREATE OR REPLACE TABLE with replication
mysql-test/suite/rpl/t/create_or_replace_statement.test:
Testing of CREATE OR REPLACE TABLE with replication
mysql-test/suite/rpl/t/rpl_gtid_startpos.test:
Test must be run in slave_ddl_exec_mode=STRICT as part of the test depends on that DROP TABLE should fail on slave.
mysql-test/suite/rpl/t/rpl_stm_log.test:
Removed some lines
mysql-test/suite/sys_vars/r/slave_ddl_exec_mode_basic.result:
Testing of slave_ddl_exec_mode
mysql-test/suite/sys_vars/t/slave_ddl_exec_mode_basic.test:
Testing of slave_ddl_exec_mode
sql/handler.cc:
Regard all tables as transactional in commit if OPTION_GTID_BEGIN is set.
This is to ensure that statments are not commited too early if non transactional tables are used.
sql/log.cc:
Regard all tables as transactional in commit if OPTION_GTID_BEGIN is set.
Also treat 'direct' log events as transactional (to get them logged as they where on the master)
sql/log_event.cc:
Ensure that the new error from DROP TABLE when trying to drop a view is treated same as the old one.
Store error code that slave expects in THD.
Set OPTION_GTID_BEGIN if we find a BEGIN.
Reset OPTION_GTID_BEGIN if we find a COMMIT.
sql/mysqld.cc:
Added slave_ddl_exec_mode_options
sql/mysqld.h:
Added slave_ddl_exec_mode_options
sql/rpl_gtid.cc:
Reset OPTION_GTID_BEGIN if we record a gtid (safety)
sql/sql_class.cc:
Regard all tables as transactional in commit if OPTION_GTID_BEGIN is set.
sql/sql_class.h:
Added to THD: log_current_statement and slave_expected_error
sql/sql_insert.cc:
Ensure that CREATE OR REPLACE is logged if table was deleted.
Don't do implicit commit for CREATE if we are under OPTION_GTID_BEGIN
sql/sql_parse.cc:
Change CREATE TABLE -> CREATE OR REPLACE TABLE for slaves
Change DROP TABLE -> DROP TABLE IF EXISTS for slaves
CREATE TABLE doesn't force implicit commit in case of OPTION_GTID_BEGIN
Don't do commits before or after any statement if OPTION_GTID_BEGIN was set.
sql/sql_priv.h:
Added OPTION_GTID_BEGIN
sql/sql_show.cc:
Enhanced store_create_info() to also be able to handle CREATE OR REPLACE
sql/sql_show.h:
Updated prototype
sql/sql_table.cc:
Ensure that CREATE OR REPLACE is logged if table was deleted.
sql/sys_vars.cc:
Added slave_ddl_exec_mode
sql/transaction.cc:
Added warning if we got a GTID under OPTION_GTID_BEGIN
The problem was a race between the SQL driver thread and the worker threads.
The SQL driver thread would set rli->last_master_timestamp to zero to
mark that it has caught up with the master, while the worker threads would
set it to the timestamp of the executed event. This can happen out-of-order
in parallel replication, causing the "caught up" status to be overwritten
and Seconds_Behind_Master to wrongly grow when the slave is idle.
To fix, introduce a separate flag rli->sql_thread_caught_up to mark that the
SQL driver thread is caught up. This avoids issues with worker threads
overwriting the SQL driver thread status. In parallel replication, we then
make SHOW SLAVE STATUS check in addition that all worker threads are idle
before showing Seconds_Behind_Master as 0 due to slave idle.
Add another test case.
Fix bug found: When one thread aborts, another thread might
wrongly advance the relay log position too far, causing the
fauling transaction to be skipped and thus lost upon
restarting the SQL thread after the failure.
The merge is still missing a few hunks related to temporary tables and
InnoDB log file size. The associated code did not seem to exist in
10.0, so the merge of that needs more work. Until this is fixed, there
are a number of test failures as a result.
Fix a couple of issues in MDEV-4506, Parallel replication:
- Missing mysql_cond_signal(), which could cause hangs.
- Fix incorrect update of old-style replication position.
- Change assertion to error handling (can trigger on manipulated/
corrupt binlog).
MDEV-5189: Error handling in parallel replication.
Fix error handling in parallel worker threads when a query fails:
- Report the error to the error log.
- Return the error back, and set rli->abort_slave.
- Stop executing more events after the error.
Do not update relay-log.info and master.info on disk after every event
when using GTID mode:
- relay-log.info and master.info are not crash-safe, and are not used
when slave restarts in GTID mode (slave connects with GTID position
instead and immediately rewrites the file with the new, correct
information found).
- When using GTID and parallel replication, the position in
relay-log.info is misleading at best and simply wrong at worst.
- When using parallel replication, the fact that every single
transaction needs to do a write() syscall to the same file is
likely to become a serious bottleneck.
The files are still written at normal slave stop.
In non-GTID mode, the files are written as normal (this is needed to
be able to restart after slave crash, even if such restart is then not
crash-safe, no change).
Fix some more parts of old-style position updates.
Now we save in rgi some coordinates for master log and relay log, so
that in do_update_pos() we can use the right set of coordinates with
the right events.
The Rotate_log_event::do_update_pos() is fixed in the parallel case
to not directly update relay-log.info (as Rotate event runs directly
in the driver SQL thread, ahead of actual event execution). Instead,
group_master_log_file is updated as part of do_update_pos() in each
event execution.
In the parallel case, position updates happen in parallel without
any ordering, but taking care that position is not updated backwards.
Since position update happens only after event execution this leads
to the right result.
Also fix an access-after-free introduced in an earlier commit.
Fix some part of update of old-style coordinates in parallel replication:
- Ignore XtraDB request for old-style coordinates, not meaningful for
parallel replication (must use GTID to get crash-safe parallel slave).
- Only update relay log coordinates forward, not backwards, to ensure
that parallel threads do not conflict with each other.
- Move future_event_relay_log_pos to rgi.
-row_stmt_start_timestamp
-last_event_start_time
-long_find_row_note
-trans_retries
Added slave_executed_entries_lock to protect rli->executed_entries
Added primitives for thread safe 64 bit increment
Update rli->executed_entries when event has executed, not when event has been sent to sql execution thread
sql/log_event.cc:
row_stmt_start and long_find_row_note is now in rpl_group_info
sql/mysqld.cc:
Added slave_executed_entries_lock to protect rli->executed_entries
sql/mysqld.h:
Added slave_executed_entries_lock to protect rli->executed_entries
Added primitives for thread safe 64 bit increment
sql/rpl_parallel.cc:
Update rli->executed_entries when event has executed, not when event has been sent to sql execution thread
sql/rpl_rli.cc:
Moved row_stmt_start_timestamp, last_event_start_time and long_find_row_note from Relay_log_info to rpl_group_info
sql/rpl_rli.h:
Moved trans_retries, row_stmt_start_timestamp, last_event_start_time and long_find_row_note from Relay_log_info to rpl_group_info
sql/slave.cc:
Use rgi for trans_retries and last_event_start_time
Update rli->executed_entries when event has executed, not when event has been sent to sql execution thread
Reset trans_retries when object is created
- Made slaves temporary table multi-thread slave safe by adding mutex around save_temporary_table usage.
- rli->save_temporary_tables is the active list of all used temporary tables
- This is copied to THD->temporary_tables when temporary tables are opened and updated when temporary tables are closed
- Added THD->lock_temporary_tables() and THD->unlock_temporary_tables() to simplify this.
- Relay_log_info->sql_thd renamed to Relay_log_info->sql_driver_thd to avoid wrong usage for merged code.
- Added is_part_of_group() to mark functions that are part of the next function. This replaces setting IN_STMT when events are executed.
- Added is_begin(), is_commit() and is_rollback() functions to Query_log_event to simplify code.
- If slave_skip_counter is set run things in single threaded mode. This simplifies code for skipping events.
- Updating state of relay log (IN_STMT and IN_TRANSACTION) is moved to one single function: update_state_of_relay_log()
We can't use OPTION_BEGIN to check for the state anymore as the sql_driver and sql execution threads may be different.
Clear IN_STMT and IN_TRANSACTION in init_relay_log_pos() and Relay_log_info::cleanup_context() to ensure the flags doesn't survive slave restarts
is_in_group() is now independent of state of executed transaction.
- Reset thd->transaction.all.modified_non_trans_table() if we did set it for single table row events.
This was mainly for keeping the flag as documented.
- Changed slave_open_temp_tables to uint32 to be able to use atomic operators on it.
- Relay_log_info::sleep_lock -> rpl_group_info::sleep_lock
- Relay_log_info::sleep_cond -> rpl_group_info::sleep_cond
- Changed some functions to take rpl_group_info instead of Relay_log_info to make them multi-slave safe and to simplify usage
- do_shall_skip()
- continue_group()
- sql_slave_killed()
- next_event()
- Simplifed arguments to io_salve_killed(), check_io_slave_killed() and sql_slave_killed(); No reason to supply THD as this is part of the given structure.
- set_thd_in_use_temporary_tables() removed as in_use is set on usage
- Added information to thd_proc_info() which thread is waiting for slave mutex to exit.
- In open_table() reuse code from find_temporary_table()
Other things:
- More DBUG statements
- Fixed the rpl_incident.test can be run with --debug
- More comments
- Disabled not used function rpl_connect_master()
mysql-test/suite/perfschema/r/all_instances.result:
Moved sleep_lock and sleep_cond to rpl_group_info
mysql-test/suite/rpl/r/rpl_incident.result:
Updated result
mysql-test/suite/rpl/t/rpl_incident-master.opt:
Not needed anymore
mysql-test/suite/rpl/t/rpl_incident.test:
Fixed that test can be run with --debug
sql/handler.cc:
More DBUG_PRINT
sql/log.cc:
More comments
sql/log_event.cc:
Added DBUG statements
do_shall_skip(), continue_group() now takes rpl_group_info param
Use is_begin(), is_commit() and is_rollback() functions instead of inspecting query string
We don't have set slaves temporary tables 'in_use' as this is now done when tables are opened.
Removed IN_STMT flag setting. This is now done in update_state_of_relay_log()
Use IN_TRANSACTION flag to test state of relay log.
In rows_event_stmt_cleanup() reset thd->transaction.all.modified_non_trans_table if we had set this before.
sql/log_event.h:
do_shall_skip(), continue_group() now takes rpl_group_info param
Added is_part_of_group() to mark events that are part of the next event. This replaces setting IN_STMT when events are executed.
Added is_begin(), is_commit() and is_rollback() functions to Query_log_event to simplify code.
sql/log_event_old.cc:
Removed IN_STMT flag setting. This is now done in update_state_of_relay_log()
do_shall_skip(), continue_group() now takes rpl_group_info param
sql/log_event_old.h:
Added is_part_of_group() to mark events that are part of the next event.
do_shall_skip(), continue_group() now takes rpl_group_info param
sql/mysqld.cc:
Changed slave_open_temp_tables to uint32 to be able to use atomic operators on it.
Relay_log_info::sleep_lock -> Rpl_group_info::sleep_lock
Relay_log_info::sleep_cond -> Rpl_group_info::sleep_cond
sql/mysqld.h:
Updated types and names
sql/rpl_gtid.cc:
More DBUG
sql/rpl_parallel.cc:
Updated TODO section
Set thd for event that is execution
Use new is_begin(), is_commit() and is_rollback() functions.
More comments
sql/rpl_rli.cc:
sql_thd -> sql_driver_thd
Relay_log_info::sleep_lock -> rpl_group_info::sleep_lock
Relay_log_info::sleep_cond -> rpl_group_info::sleep_cond
Clear IN_STMT and IN_TRANSACTION in init_relay_log_pos() and Relay_log_info::cleanup_context() to ensure the flags doesn't survive slave restarts.
Reset table->in_use for temporary tables as the table may have been used by another THD.
Use IN_TRANSACTION instead of OPTION_BEGIN to check state of relay log.
Removed IN_STMT flag setting. This is now done in update_state_of_relay_log()
sql/rpl_rli.h:
Changed relay log state flags to bit masks instead of bit positions (most other code we have uses bit masks)
Added IN_TRANSACTION to mark if we are in a BEGIN ... COMMIT section.
save_temporary_tables is now thread safe
Relay_log_info::sleep_lock -> rpl_group_info::sleep_lock
Relay_log_info::sleep_cond -> rpl_group_info::sleep_cond
Relay_log_info->sql_thd renamed to Relay_log_info->sql_driver_thd to avoid wrong usage for merged code
is_in_group() is now independent of state of executed transaction.
sql/slave.cc:
Simplifed arguments to io_salve_killed(), sql_slave_killed() and check_io_slave_killed(); No reason to supply THD as this is part of the given structure.
set_thd_in_use_temporary_tables() removed as in_use is set on usage in sql_base.cc
sql_thd -> sql_driver_thd
More DBUG
Added update_state_of_relay_log() which will calculate the IN_STMT and IN_TRANSACTION state of the relay log after the current element is executed.
If slave_skip_counter is set run things in single threaded mode.
Simplifed arguments to io_salve_killed(), check_io_slave_killed() and sql_slave_killed(); No reason to supply THD as this is part of the given structure.
Added information to thd_proc_info() which thread is waiting for slave mutex to exit.
Disabled not used function rpl_connect_master()
Updated argument to next_event()
sql/sql_base.cc:
Added mutex around usage of slave's temporary tables. The active list is always kept up to date in sql->rgi_slave->save_temporary_tables.
Clear thd->temporary_tables after query (safety)
More DBUG
When using temporary table, set table->in_use to current thd as the THD may be different for slave threads.
Some code is ifdef:ed with REMOVE_AFTER_MERGE_WITH_10 as the given code in 10.0 is not yet in this tree.
In open_table() reuse code from find_temporary_table()
sql/sql_binlog.cc:
rli->sql_thd -> rli->sql_driver_thd
Remove duplicate setting of rgi->rli
sql/sql_class.cc:
Added helper functions rgi_lock_temporary_tables() and rgi_unlock_temporary_tables()
Would have been nicer to have these inline, but there was no easy way to do that
sql/sql_class.h:
Added functions to protect slaves temporary tables
sql/sql_parse.cc:
Added DBUG_PRINT
sql/transaction.cc:
Added comment
Implement @@gtid_binlog_state. This is the internal state of the binlog
(most recent GTID logged for every domain_id and server_id). This allows
to save the state before RESET MASTER and restore it afterwards.
STATUS OF ROLLBACKED TRANSACTION" and bug #17054007 - "TRANSACTION
IS NOT FULLY ROLLED BACK IN CASE OF INNODB DEADLOCK".
The problem in the first bug report was that although deadlock involving
metadata locks was reported using the same error code and message as InnoDB
deadlock it didn't rollback transaction like the latter. This caused
confusion to users as in some cases after ER_LOCK_DEADLOCK transaction
could have been restarted immediately and in some cases rollback was
required.
The problem in the second bug report was that although InnoDB deadlock
caused transaction rollback in all storage engines it didn't cause release
of metadata locks. So concurrent DDL on the tables used in transaction was
blocked until implicit or explicit COMMIT or ROLLBACK was issued in the
connection which got InnoDB deadlock.
The former issue has stemmed from the fact that when support for detection
and reporting metadata locks deadlocks was added we erroneously assumed
that InnoDB doesn't rollback transaction on deadlock but only last statement
(while this is what happens on InnoDB lock timeout actually) and so didn't
implement rollback of transactions on MDL deadlocks.
The latter issue was caused by the fact that rollback of transaction due
to deadlock is carried out by setting THD::transaction_rollback_request
flag at the point where deadlock is detected and performing rollback
inside of trans_rollback_stmt() call when this flag is set. And
trans_rollback_stmt() is not aware of MDL locks, so no MDL locks are
released.
This patch solves these two problems in the following way:
- In case when MDL deadlock is detect transaction rollback is requested
by setting THD::transaction_rollback_request flag.
- Code performing rollback of transaction if THD::transaction_rollback_request
is moved out from trans_rollback_stmt(). Now we handle rollback request
on the same level as we call trans_rollback_stmt() and release statement/
transaction MDL locks.
includes:
* remove some remnants of "Bug#14521864: MYSQL 5.1 TO 5.5 BUGS PARTITIONING"
* introduce LOCK_share, now LOCK_ha_data is strictly for engines
* rea_create_table() always creates .par file (even in "frm-only" mode)
* fix a 5.6 bug, temp file leak on dummy ALTER TABLE
Fix a bunch of issues found with locking, ordering, and non-thread-safe stuff
in Relay_log_info.
Now able to do a simple benchmark, showing 4.5 times speedup for applying a
binlog with 10000 REPLACE statements.
Fix some bugs around waiting for worker threads to end during SQL slave stop.
Free Log_event after parallel execution (still needs to be made thread-safe by
using rpl_group_info rather than rli).
Hook in the wait-for-prior-commit logic (not really tested yet).
Clean up some resource maintenance around rpl_group_info (may still be some
smaller issues there though).
Add a ToDo list at the top of rpl_parallel.cc
When we load the slave state from the mysql.gtid_slave_pos at server start, we
need to load all the rows into the in-memory hash, not just the most recent
one in each replication domain. Otherwise we accumulate cruft in the form of
old rows each time the server restarts.
