Two problems were fixed:

1. When not in GTID mode (master_use_gtid=no), then we must not apply events
   in different domains in parallel (in non-GTID mode we are not capable of
   restarting at different points in different domains).

2. When transactions B and C group commit together, but after and separate
   from A, we can apply B and C in parallel, but both B and C must not start
   until A has committed. Fix sub_id to be globally increasing (not just
   per-domain increasing) so that this wait (which is based on sub_id) can be
   done correctly.

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 uninitialised variable.

Implement --slave-parallel-max-queue to limit memory usage
of SQL thread read-ahead in the relay log.

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.

Flush the proc file after every modifications. This will avoid errors of type "Table './mysql/proc' is marked as crashed and should be repaired"

Moved the remaining variables, that depends on sql execution, from Relay_log_info to rpl_group_info:
-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

Add an error code to the wait_for_commit facility.

Now, when a transaction fails, it can signal the error to
any subsequent transaction that is waiting for it to commit.
The waiting transactions then receive the error code back from
wait_for_prior_commit() and can handle the error appropriately.

Also fix one race that could cause crash if @@slave_parallel_threads
were changed several times quickly in succession.

- 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

This helps when moving from MariaDB 5.5 to MariaDB 10.0 as sometimes the log file size is rounded differently.

storage/innobase/srv/srv0start.c:
  Give a warning, not an error, if the log file size in innodb doesn't match what is on disk
storage/xtradb/srv/srv0start.c:
  Give a warning, not an error, if the log file size in innodb doesn't match what is on disk

Improve STOP SLAVE in parallel mode.

Now, the parallel part will queue the current event group to the
end, and then stop queing any more events. Each worker will
complete the current event group, and then just skip any further
queued events.

Remove some unnecessary mutex locking.

Add another test case.

Add another test case, using DEBUG_SYNC.
Fix one bug found.

Add comments explaining tricky memory barrier semantics and
suggestions for future changes.

Add a simple test case.
Fix bugs found.

Some after-review fixes.

Move annotate-event stuff from Relay_log_info to rpl_group_info,
to make it thread safe.

Remove Relay_log_info::group_info. (It is not thread safe).

Move the deferred event stuff from Relay_log_info to rpl_group_info
to make it thread safe for parallel replication.

Fix a number of failures in the test suite.

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.

Impement options --binlog-commit-wait-count and
--binlog-commit-wait-usec.

These options permit the DBA to deliberately increase latency
of an individual commit to get more transactions in each
binlog group commit. This increases the opportunity for
parallel replication on the slave, and can also decrease I/O
load on the master.

The options also make it easier to test the parallel
replication with mysql-test-run.

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).

Wait for all worker threads to finish when stopping the SQL thread.
(Only a basic wait; this still needs to be fixed to include timeout
logic as in sql_slave_killed()).

Pass down rpl_group_info * to remove one instance of non-threadsafe
use of rli->group_info.

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

First step of splitting out part of Relay_log_info, so that different
event groups being applied in parallel can each use their own copy.

Implement facility for the commit in one thread to wait for the commit of
another to complete first. The wait is done in a way that does not hinder
that a waiter and a waitee can group commit together with a single fsync()
in both binlog and InnoDB. The wait is done efficiently with respect to
locking.

The patch was originally made to support TaoBao parallel replication with
in-order commit; now it will be adapted to also be used for parallel
replication of group-committed transactions.

A waiter THD registers itself with a prior waitee THD. The waiter will then
complete its commit at the earliest in the same group commit of the waitee
(when using binlog). The wait can also be done explicitly by the waitee.

Fix typo in worker thread free list management.
Simple parallel INSERT from worker threads runs now.

A few fixes following tests. Now can apply one INSERT event in
a separate worker thread.

First very rough sketch. We spawn and retire a pool of slave threads.
Test main.alias works, most likely not much else does.

Now whenever we reach the GTID point requested from the slave (when using GTID
position to connect), we send a fake Gtid_list event. This event is used by
the slave to know the current old-style position for MASTER_POS_WAIT(), and
later the similar binlog position for MASTER_GTID_WAIT().

Without this fake event, if the slave is already fully up-to-date with the
master, there may be no events sent at the given position for an indeterminate
time.

If the mysql.gtid_slave_pos table is not available, we cannot load nor update
the current GTID position persistently. This can happen eg. after an upgrade,
before mysql_upgrade_db is run, or if the table is InnoDB and the server is
restarted without the InnoDB storage engine enabled.

Before, replication always failed to start if the table was unavailable. With
this patch, we try to continue with old-style replication, after suitable
complaints in the error log. In strict mode, or if slave is configured to use
GTID, slave still refuses to start.