HighLoad++ 2017 Зал «Кейптаун», 8 ноября, 13:00 Тезисы: http://www.highload.ru/2017/abstracts/2954.html MySQL Replication is powerful and has added a lot of advanced features through the years. In this presentation we will look into replication technology in MySQL 5.7 and variants focusing on advanced features, what do they mean, when to use them and when not, Including. When should you use STATEMENT, ROW or MIXED binary log format? What is GTID in MySQL and MariaDB and why do you want to use them? What is semi-sync replication and how is it different from lossless semi-sync? ...

1. © 2017 Percona1
Peter Zaitsev, CEO
Advanced MySQL Replication Features
Highload++ Moscow, Russia
November 8, 2017

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In This Presentation
Few Words about Replication & Availability
MySQL Replication Timeline
Advanced MySQL Replication Options

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Few Words about Replication

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Replication
Having Multiple Copies of the
data, updated with changes

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Why Replication
Availability Scalability Performance

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Availability
Service Stays up when
component fails

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Availability via Redundancy
Have more than one system
Works well for stateless systems
Is not enough for databases

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Availability via Replication
Redundant
Computing
Resource
Paired with
Replicated
Data

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Component Failure
• Total Crash
• Process Crash
• Stall/Unresponsive
• Consistency Issues
Node
Failures
• Single Network Port Failures
• Network Device Failures
• Partitions
• Complicated Failures
Network
Failures

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Scalability with Replication
Scales Reads
Does not Scale Writes very well
Data Distribution is needed for scaling writes

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Performance
Reduce response time by
maintaining replica closer to user
Better Performance Through
avoiding resource saturation

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Replication in MySQL
A brief Time Line

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MySQL Replication
MySQL 3.23
• Initial
Statement
Replication
Implemented
MySQL 4.0
• Split IO
Thread and
SQL Thread
MySQL 5.1
• Row and
Mixed
replication
modes
supported
MySQL 5.6
• Per Database
Parallel
Replication
• GTID Support
MySQL 5.7
• General
Parallel
Replication
• Multi-Source
Replication
• Group
Replication /
MySQL
Innodb
Cluster

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Galera Based Replication
Technology
Similar to MySQL Group
Replication but more mature
Available for MySQL,
Percona, MariaDB
Alternative Track

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Replication in MariaDB
Is not 100% Same as in MySQL
Different GTID Implementation
Different parallel replication
Not instrumented in the same way
Number of features became available in MariaDB Earlier
Not covering MariaDB in this Presentation

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Advanced Replication

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What is Basic Replication ?
Statement
Replication
Replication of
the Full
Database
Using Binary Log
Position
Single Tier
Topology
Single Thread Asynchronous
Write to Single
Master
Keep Slave
Meta-Data Data
in Files
Master-Slave-
Replication
Manual Failover
& Traffic
Management

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Statement vs Row Replication
•STATEMENT
•ROW
•MIXED
Configured on
the Master as
binlog_format

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How Rows are Logged ?
•Full
•Minimal
•Noblob
binlog_row_image

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Missing Seeing Queries ?
Also Log Query For informational Purposes
binlog_rows_query_log_events
Off by Default

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Replication of Full Database
Full Replication Most Simple for Troubleshooting and
Recovery
Can replicate only portions of the database
Can add additional data to the slaves

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Replication Filering
• Binlog_do_db
• Binlog_ignore_db
On the Master
(writing binary
log)
• Replicate_do_db
• Replicate_ignore_db
• Replicate_wild_do_table
• Replicate_wild_ignore_table
On the Slave

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Position Identification
By Binary Log
Position
•File: mysql-
bin.000003
•Position: 73
By GTID
•3E11FA47-71CA-
11E1-9E33-
C80AA9429562:23

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What is in GTID ?
GTID = source_id:transaction_id
Source_id is Server_uuid of Originating Server
Always Preserved on the Slaves
Track which transactions executed
mysql.gtid_executed table (5.7) + binlog

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GTID Benefits and Drawbacks
Automatic Position Discovery
Easy Slave Promotion
Discovery of Missed Transactions
Pain in the Ass with Manual Troubleshooting

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Replication Topologies
Single Tier Master-Slave
Bi-Directional
Tree
Ring
Directed Graph

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Options For Complicated Topologies
•Store copy of applied
statements in local binlog
•Disabled by default until
MySQL 8
Log_slave_updates

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Parallel Replication
Single Thread Replication is typical limiting factor
Parallel Replication for multiple Databases since 5.6
Parallel Replication for same table since 5.7

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Managing Parallel Replication
slave-parallel-workers
slave-parallel-type=DATABASE|LOGICAL_CLOCK
slave_preserve_commit_order

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Asynchronous Replication
Default in MySQL
There is no guaranty of Timeliness
“Replication Lag” can be days… and weeks
Support for Semi-Synchronous Replication
Support for Virtually Synchronous Group Replication

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Sync or Async
Synchronous
Replication
Asynchronous
Replication

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Synchronous Replication
Data “Persisted” on Target Server
Guarantees No Data Loss if Source server fails
Conflicts can be easily prevented
Expensive

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Persistence in terms of
Durability – In case of original node loss, can date be
recovered?
Visibility – Is data visible by reads going to secondary node
Both Required for truly synchronous replication

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What “Persisted” means ?
•Assumes power loss of both
servers does not happen
In
Memory
•Handles Total Loss of Master
and Power loss on the SlaveOn Disk

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Asynchronous Replication
Anything not Synchronous
Many different variants exist!

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Asynchronous Properties
•What happens with
Persistence ?
•What happens with
Visibility ?
Commit
on
Master

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Persistence
Uncommitted Data on Master
Committed Data on Master
Data in Slave’s memory
Data on Slave’s Disk (log)

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Visibility
•Phantom Reads
Results be visible by
concurrent sessions
before
acknowledgement
•No Phantom Reads
Results can’t be
visible by
concurrent sessions

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Semi-Synchronous Replication in MySQL
• Both on Master and SlavePlugin Required
• INSTALL PLUGIN rpl_semi_sync_master
SONAME 'semisync_master.so';Master
• INSTALL PLUGIN rpl_semi_sync_slave
SONAME 'semisync_slave.so';Slave

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Semi-Sync Replication Options
Master: rpl_semi_sync_master_enabled
Master: rpl_semi_sync_master_timeout
Master: rpl_semi_sync_master_wait_point=AFTER_SYNC|AFTER_COMMIT
Master: rpl_semi_sync_master_wait_for_slave_count
Slave: rpl_semi_sync_slave_enabled

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Where Do We Write ?
Single Master Multi-Master

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Single Master
All writes go to the single node
One way replication stream
Simple
No Conflicts
Replication aware Application or Connector

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Active-Passive Master-Master
Replication is bi-directional
Only one Master can be written at the same time
Essentially Single Master if configured well
Minefield if not configured well

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Multiple Active Masters
Can write to multiple masters
Replication is multi-directional
More Complicated
Possibility of Conflicts

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MySQL Replication Multi-Master
Recipe for problems with Async/SemiSync Replication
Design Application to Avoid Conflicts
MySQL Group Replication
PXC/Galera Based Solutions

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Multi-Master with MySQL Replication
auto_increment_offset
auto_increment_increment
slave_exec_mode=idempotent

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Replication Position information
Master_info_repository=FILE|TABLE
Relay_log_info_repository=FILE|TABLE
Sync_master_info
Sync_relay_log_info
Relay_log_recovery
Less Problem with GTID Replication

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Master Slave Replication ?
Most Commonly Used Variant
MySQL Group Replication is other Option
Percona XtraDB Cluster/Galera - Community Alternative

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MySQL Group Replication Overview
Inspired by Galera Ideas (and Success)
Built on top of standard MySQL Replication
Available as Plugin for MySQL 5.7
Considered GA but really very early product

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Difference from MySQL Replication
No Master/Slave but Group Membership
Transactions are committed when they are certified by majority of nodes (Paxos)
Does not accept writes if there is no Quorum
Flow Control to prevent unlimited replication lag
Nodes encountering inconsistency leave the cluster
Conflict Detection and Resolution (or avoidance)
Simple FailOver

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MySQL Group Replication - Writes
By Default configures itself as Single
Primary
Can configure to allow writes to any
node

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MySQL Group Replication Limitations
No Automated node Provisioning
Manual Recovery of failed nodes
No way (yet) to ensure node does not read stale data

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MySQL Innodb Cluster

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Failover and Traffic Management
How do we Re-Configure Replication if Master Crashes ?
How do we Makes Sure Application uses Right Master ?
How do we get Slave used by Application ?

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Making MySQL Replication Better
MHA
MySQL Failover
Orchestrator

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Orchestrator Screenshot

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Traffic Management Solutions
• Not Immediate, Does not handle existing connectionsDNS
• TCP/IP Port level. Does not understand MySQL ProtocolHAProxy
• Like HA Proxy in the CloudElastic Load Balancer (etc)
• Currently very basicMySQL Router
• Proprietary SolutionsMaxScale, ScaleArc
• MySQL Protocol Aware 100% Open Source Proxy Solution for MySQLProxySQL

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We integrate ProxySQL with PXC
High Availability
Multiplexing (Connection Pooling)
Caching
Read/write Splitting
Easy Configuration with proxysql-admin
Can run in dedicated writer and load balanced mode

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Dedicated shared ProxySQL 5
9
application server 1 application server 2 application server 3
PXC node 1 PXC node 2 PXC node 3
ProxySQL

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ProxySQL on application side
application server 1 application server 2 application server 3
PXC node 1 PXC node 2 PXC node 3
6
0
ProxySQL ProxySQL ProxySQL

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ProxySQL at PMM

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