MySQL 5.7 Replication News

Copyright © 2015, Oracle and/or its affiliates. All rights reserved. |Tuesday, October 20, 2015 Oracle Confidential – Restricted
MySQL 5.7 Replication Update
Ted Wennmark (ted.wennmark@oracle.com)
MySQL EMEA Techtour
1
The Latest and Greatest MySQL 5.7 Replication Features and More!

Copyright © 2015, Oracle and/or its affiliates. All rights reserved. |
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Tuesday, October 20, 2015 Oracle Confidential – Restricted 2

Program Agenda
Background
Replication Features in MySQL 5.7
News From The Lab!
The Road Ahead!
1
2
3
4

Background1
Tuesday, October 20, 2015 Oracle Confidential – Restricted

Background: Replication Components
Tuesday, October 20, 2015
Insert...
Insert...
B
binary log
Insert...
relay log
Insert...
A
binary log
Client
Sender
thread
Receiver
thread
Applier
Threads
Receiver
Meta-data
Update
Applier
Meta-data
Update
Network
Oracle Confidential – Restricted 5

Background: Replication Components
• Binary Log
– File based logical log that records the changes on the master.
– Statement or Row based format (may be intermixed).
– Each transactions is split into groups of events.
– Control events: Rotate, Format Description, Gtid, ...
Layout of a
Binary Log File
BEGIN ...E1 E2 COMMIT BEGIN ...E1 E2 COMMIT

M S
S
S
S
M
write clients read clients
read clients
write clients
More
reads?
More
slaves!
Read scale-out
Background: What is Replication Used For?

M M?
write clients write clients
More
writes?
More
Masters?
M?
M?
MySQL Fabric helps sharding your data with MySQL...
What about write scale-out?

C
B
A
C
B
ACrash
C
B
A
B is the
new master
Uh Oh! Whew!
Redundancy: If master crashes, promote slave to master

M
S
write clients
business intelligent client applications
reporting client applications
big queries client applications
On-line Backup and Reporting

CB
BA
AC
Image from
www.ginkgomaps.com

Usability / Online
2
2.1
Oracle Confidential – Restricted

Online Reconfiguration of Global Transaction Identifiers
Insert...
Insert...
B
binary log
Insert...
relay log
Insert...
A
binary log
Client
Sender
thread
Receiver
thread
Applier
Threads
Receiver
Meta-data
Update
Applier
Meta-data
Update
Network

• The procedure is online.
– Both reads and writes are allowed while global transaction identifiers are being
turned on or off in the entire replication cluster.
• No need to synchronize servers, ever.
• No need to restart servers.
• No need to change replication topology.
– Works in arbitrary topologies.
• Should anything happen in the middle of the procedure, you can always roll
back.

• Over simplified procedure to turn on global transaction identifiers:
• Details: http://dev.mysql.com/doc/refman/5.7/en/replication-mode-
change-online-enable-gtids.html
( SET @@GLOBAL.ENFORCE_GTID_CONSISTENCY = WARN | ON)
1)SET @@GLOBAL.GTID_MODE = OFF_PERMISSIVE; (on every server)
2) SET @@GLOBAL.GTID_MODE = ON_PERMISSIVE; (on every server)
3) wait for a bit longer than your replication lag
4) SET @@GLOBAL.GTID_MODE = ON; (on every server)

Online Reconfiguration of Replication Filters
Insert...
Insert...
B
binary log
Insert...
relay log
Insert...
A
binary log
Client
Sender
thread
Receiver
thread
Applier
Threads
Receiver
Meta-data
Update
Applier
Meta-data
Update
Network

Online Reconfiguration of Replication Filters
• Change Slave's Replication Filters dynamically.
– No need to stop and restart the slave server for setting new replication filtering rules.
– All slave filters are supported.
– Values can be input in various character sets.
mysql> CHANGE REPLICATION FILTER REPLICATE_DO_DB= (db1, db2)

Online Switch/Fail-over to a new Master
Insert...
Insert...
B
binary log
Insert...
relay log
Insert...
A
binary log
Client
Sender
thread
Receiver
thread
Applier
Threads
Receiver
Meta-data
Update
Applier
Meta-data
Update
Network

Change master from A to B without stopping the applier threads.
C
B
A
C
B
ACrash
C
B
A
B is the
new master
Uh Oh! Whew!

Change master from A to B without stopping the applier threads.
C
B
A
C
B
ACrash
C
B
A
Uh Oh! Whew!
DBA did not need C to stop applying its
relay log to change C's master from A to B.

• Enables more online operations during fail-over:
• Stopping, changing master and restarting the receiver thread are all done
while the applier thread is running.
• Change applier properties while the receiver thread is working:
mysql> STOP SLAVE IO_THREAD;
mysql> CHANGE MASTER TO MASTER_HOST='master2', …;
mysql> START SLAVE IO_THREAD;
mysql> STOP SLAVE SQL_THREAD;
mysql> CHANGE MASTER TO MASTER_DELAY=3600, …;
mysql> START SLAVE SQL_THREAD;

Improved Replication Monitoring
Insert...
Insert...
B
binary log
Insert...
relay log
Insert...
A
binary log
Client
Sender
thread
Receiver
thread
Applier
Threads
Receiver
Meta-data
Update
Applier
Meta-data
Update
Network
DBA

• Monitoring through SQL.
• Logically unrelated information into different places.
• Extensible, can be adapted to new features.
• More accurate and consistent identifier names.
• Master-slave, Multi-source, Group Replication support.
Performance Schema Replication Tables

mysql> select * from performance_schema.replication_applier_status_by_workerG
*************************** 1. row ***************************
CHANNEL_NAME:
WORKER_ID: 1
THREAD_ID: 35
SERVICE_STATE: ON
LAST_SEEN_TRANSACTION: 4ba0eb86-63c3-11e4-92ba-28b2bd168d07:2368
LAST_ERROR_NUMBER: 0
LAST_ERROR_MESSAGE:
LAST_ERROR_TIMESTAMP: 0000-00-00 00:00:00
*************************** 2. row ***************************
CHANNEL_NAME:
WORKER_ID: 2
THREAD_ID: 36
SERVICE_STATE: ON
LAST_SEEN_TRANSACTION: 4ba0eb86-63c3-11e4-92ba-28b2bd168d07:2367
LAST_ERROR_NUMBER: 0
LAST_ERROR_MESSAGE:
LAST_ERROR_TIMESTAMP: 0000-00-00 00:00:00
2 rows in set (0,00 sec)

Usability / Online
Performance
2
2.1
2.2

Improved Applier Throughput – Locking-based Parallelism
Insert...
Insert...
B
binary log
Insert...
relay log
Insert...
A
binary log
Client
Sender
thread
Receiver
thread
Applier
Threads
Receiver
Meta-data
Update
Applier
Meta-data
Update
Network

Single Threaded Apply 8 Threads Applier 24 Threads Applier 48 Threads Applier 96 Threads Applier
0%
50%
100%
150%
200%
250%
Fast and Scalable Multi-threaded Replication Applier
(statement-based replication, durable settings, SSD storage)
Slaveapplytime
(SysbenchRWonthemasterwith96threads=100%)
10X

• Leverage parallelization information from master execution:
– Concurrent transactions, which have not blocked each other on the master, are
marked as non-contending in the binary log.
• Meanwhile, at the slave:
– Non-contending transactions are scheduled in parallel;
– Concurrent transactions commit independently, thus no waiting involved.

• T2 is scheduled to execute
together with T1.
• T3 is scheduled to execute
as soon as T1 finishes.
T1
T2
T3
Time
Commit Finishes
Last Lock Acquired
Concurrent Execution History
on the Master
Execution
Commit
T1 and T2 execute in
parallel on the slave.
T2 and T3 execute in
parallel on the slave.

• Supports statement-based or row-based formats.
• Scheduling policy controlled through:
– logical_clock - means schedule based on the locking interval timestamps.
– database - the scheduling policy from 5.6 (concurrency control done per database).
• Work to improve slave scalability continues, does not stop here.
mysql> SET slave_parallel_type= [logical_clock|database]

Improved User Threads-Sender Threads Synchronization
Insert...
Insert...
B
binary log
Insert...
relay log
Insert...
A
binary log
Client
Sender
thread
Receiver
thread
Applier
Threads
Receiver
Meta-data
Update
Applier
Meta-data
Update
Network

Improved User Threads-Sender Threads Synchronization
• Concurrent reads by the sender thread with ongoing writes from user
threads.
– Sender thread does not block user sessions more than necessary.
– Higher throughput for both sender threads and user sessions.
Sender Thread Reads Binary Log User Thread Writes to Binary Log
Sender Thread Reads Binary Log
User Thread Writes to Binary Log
pre 5.7.2
5.7.2+

Faster Semi-sync Replication – ACK Receiver Thread
Insert...
Insert...
B
binary log
Insert...
relay log
Insert...
A
binary log
Client
ACK
Receiver
thread
Receiver
thread
Applier
Threads
Receiver
Meta-data
Update
Applier
Meta-data
Update
Network
Sender
thread

Faster Semi-sync Replication – ACK Receiver Thread
• Consecutive transactions do not block each other while waiting for ACKs
– Transaction t1 and t2 are sent immediately to the slave by the sender thread
– ACKs are received only by a special thread
– Transaction t2 does not include t1 round trip in its semi-sync overall latency
• Thread starts when semi-sync is activated
• Thread stops when semi-sync is deactivated
mysql> SET GLOBAL rpl_semi_master_enabled= ON
mysql> SET GLOBAL rpl_semi_master_enabled= OFF

Usability / Online
Performance
Improved reliability
2
2.1
2.2
2.3

Loss-less Semi-sync Replication
Insert...
Insert...
B
binary log
Insert...
relay log
Insert...
A
binary log
Client
Sender
thread
Receiver
thread
Applier
Threads
Receiver
Meta-data
Update
Applier
Meta-data
Update
Network

Master
Slave
T1: INSERT INTO t1 VALUES (1000)
ACK
Time
T2: SELECT * FROM t1; empty set
execute prepare binlog
relay log
commitexecute

• Master waits for slave's ACK before committing (as opposed to: master
waits for slave's ACK after committing).
– Therefore, concurrent transactions do not see changes while this transaction waits for
ack.
• Should a master fail, then any transaction that it may have externalized is
also persisted on a slave.
• User can choose between the original semi-sync behavior and the new
one.
mysql> SET rpl_semi_sync_master_wait_point= [AFTER_SYNC|AFTER_COMMIT]

Semi-sync Replication – Wait for Multiple ACKs
Insert...
Insert...
B
binary log
Insert...
relay log
Insert...
A
binary log
Client
Sender
thread
Receiver
thread
Applier
Threads
Receiver
Meta-data
Update
Applier
Meta-data
Update
Network

• Master does not commit transaction until it receives N ACKs from N slaves.
• Dynamically settable:
mysql> SET GLOBAL rpl_semi_sync_master_wait_for_slave_count= N

• Master does not commit transaction until it receives N ACKs from N slaves.
• Dynamically settable:
mysql> SET GLOBAL rpl_semi_sync_master_wait_for_slave_count= N
Master
Slave 2
T1: COMMIT
ACK
Slave 1
ACK
T1: COMMIT
succeeds
mysql> SET GLOBAL rpl_semi_sync_master_wait_for_slave_count= 2
Slave 3
Time
relay log
relay log
relay log
ACK

Usability / Online
Performance
Improved reliability
Flexibility
2
2.1
2.2
2.3
2.4

Storing Global Transaction Identifiers in a Table
Insert...
B
Insert...
relay log
Insert...
A
binary log
Client
Sender
thread
Receiver
thread
Applier
Threads
Receiver
Meta-data
Update
Applier
Meta-data
Update
Network

Storing Global Transaction Identifiers in a Table
• Slaves can use GTIDs with binary logs disabled.
– Slaves that are never candidates to become a master can still use GTIDs for auto
positioning.
Use Cases

Multi-Source Replication
S
M M Slave can have more than one master.M M
The need for gathering data in a central server:
• Integrated backup;
• Complex queries for analytics purposes;
• Data HUB for inter-cluster replication.

Multi-Source Replication II
• A server (slave) can replicate from multiple sources (masters).
• Multiple channels (channel: connection thread, relay log, applier threads)
that can be stopped started individually.
• Integrated with Multi-threaded Slave.
– Each channel has its own multi-threaded applier set of threads.
• Integrated with the new P_S tables.
– replication_applier_status_by_coordinator shows multiple entries, one per
channel/source applier.
– replication_connection_status shows multiple entries, one per connection to
different sources.

Multi-Source Replication III
• Integrated with GTIDs.
• Integrated with crash-safe tables.
– Progress state is stored in these tables for recoverability purposes.
• Virtually no limit on the number of sources (capped to 256, but can be
changed if server binary is rebuilt).

The Road Ahead!4
Tuesday, October 20, 2015 Oracle Confidential – Restricted

What is Next?
• MySQL Group Replication
– Rapid releases.
– Improve performance, stability and usability.
• MySQL Replication Usability
– Instrument even more replication and extend replication P_S tables
– Simpler administrative commands
• MySQL Replication Performance
– Continue to improve multi-threaded (slave) applier
– Continue to improve semi-sync

Where to go from here?
• Packages
– http://dev.mysql.com
– http://labs.mysql.com
• Reference Documentation
– http://dev.mysql.com/doc/#manual
• Blogs from the Engineers (news, quirks, technical information and much
more)
– http://mysqlhighavailability.com

MySQL 5.7 Replication News

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