MySQL 5.6 Replication for ArchitectsKristian Köhntopp

Scale Out2

Slave Server

Master Server

Client

writes

reads(through LB)

Types of Slaves

• Standard R/O Slave.

• Slave for long running queries.

• Aggregation to secondary local schema.

• Slave for ad-hoc queries.

• Slave for fulltext searches.

• Local schema mods (Table Type, Indices).

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Multi-Level Slaves4

Slave Server

Master Server

Slave Server

Local Master Server

Heathrow Amsterdam

Multi-Level Slaves

• Intermediate Slave requires

• log_slave_updates = 1

• Loop detection: All machines require

• server_id = n

• Since 5.5: Also a machine UUID defined.

• Each machine needs their own id.

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Replication is not HA6

Slave Server

Master Server DesignatedBackup Master

binlog.000018Offset 743271

binlog.000012Offset 393273?

Replication is not HA

• Master and Backup Master have different binlog positions.

• The distance between them is not constant

• Log into Backup, enter command.

• MySQL 5.6 ff: Global Transaction ID.

• Galera!

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Ring Structures8

Server #1

Server #3

Server #2

Ring Structures

• A slave can have only one master.

• A master can have many slaves.

• A ring is a valid replication structure.

• log_slave_updates, server_id critical.

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Ring Structures

• Ring structures are fragile:

• Each ring member has its own binlog position.

• Server #2 fails, binlog position is lost.

• How do you recover?

• We try to avoid replication rings.

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Ring Structures

• Inserts into rings are complicated

• Server #1: INSERT INTO t (id, data) VALUES (NULL, 10)

• Server #2: INSERT INTO t (id, data) VALUES (NULL, 20)

• Assigned auto_increment values?

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Ring Structures

• Workaround:

• auto_increment_increment (aii) = n

• n is ring circumference

• auto_increment_offset (aio) = o

• o is server # in ring

• Server #1 assigns 0, 3, 6, Server #2 assigns 1, 4, 7

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Ring Structures

• Gaps exist:

• Server #1 can be already at 300, while Server #2 is still at 7

• Solves insert problem, but not concurrent UPDATES

• Change record 7 on two servers concurrently → instant disaster

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Ring Structures

• True multimaster solutions exist.

• All of them require 2PC or make assumptions.

• 2PC, 3PC, Paxos:

• Extremely sensitive to latency.

• That means: SLOW!

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Ring Structures

• Note:

• A ring-with-2 is not a multimaster database.

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Proper HA16

Slave Server

Master Server Backup Master

Disk Mirroror

Shared Disk

VirtualIP Number

Mobile between Hosts

Proper HA

• Master active, Backup passive

• Hard partition of capacity, no potential for overcommit.

• Master and Backup binary identical.

• binary log position interchangeable.

• Mobile Virtual IP Number

• On failure migrate VIP, restart service.

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Proper HA

• Shared Disk Solutions:

• NetApp or other SAN.

• Disk Mirror Solutions:

• DRBD or other disk update shipping (ZFS).

• Mobile VIP:

• heartbeat, pacemaker, Veritas, etc.

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