MySQL Developer Day conference: MySQL Replication and Scalability

transcript

MySQL Replication and Scalability

Shivji JhaSoftware Developer,MySQL Replication Team

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OverviewMySQL Replication: Discover What's New

Overview: MySQL Replication

Consistency: Lossless Semi-Sync

Slave Throughput: Improved Multi-Threaded Slave

Flexibility: Multi-Source Replication

Monitoring: Performance_Schema Tables

Next steps

“In my opinion, MySQL is the only database we would ever trust to power the Zappos.com website.”

"On any given day we can sell close to 300,000 tickets on the Web site using MySQL as the database to search for events. It is amazing."

"craigslist infrastructure could not have handled the exponential growth in traffic without MySQL.”

“We are one of the largest MySQL web sites in production

MySQL Replication In Action on the Web

“As a leader in our field, we are committed to providing the best service to our users, and a web experience that meets members expectations and that starts with IT”

What isReplication?

Replication: Copy Changes Master → Slave

MySQL Master Server● Changes data● Sends changes to slave

MySQL Slave Server● Receives changes from master● Applies received changes to database

M M/S S

Server can be master, slave or both

Master can have multiple slaves

Slave can only have one master

MSlave can have multiple masters!labs.mysql.com

labsYippee!

Circular replication is also possible

Filters on slave

Replicationfilter

I have a lotof tables

I only havetable_1

Why UseReplication?

Why Replication? – Performance

Read scale-out

write clients read clients

Read scale-out

write clients read clients

Morereads?More

slaves!

Read scale-out

write clients read clients read clients

write clients

Morereads?More

slaves!

Why Replication? – Redundancy

If master crashes, promote slave to master

ACrash

B is thenew master

Why Replication? – Online backup/reporting

Expensive queries on slave(s)

Regular clients

Reports Big queries Business intelligence

Why Replication? – Long-distance Data Distribution

Image fromwww.ginkgomaps.com

How DoesReplication

All Transactions Written to Binary Log

binary log

Client

create table t (a int);

binary log

Client

create table t (a int);

Table t

create...

binary log

Client

create table t (a int);insert into t values (1);

Table t

create...

binary log

Client

create table t (a int);insert into t values (1);

Table t1

create...insert...A

binary log

Client

Slave Initiates Replication

binary log

Client1. Slave sends request

for replication to startto master

2. Master sends streamof replication data

to slave

Binary Log Sent to Slave, Re-applied

binary log

Client

create...

binary log

Client

create...

Table t

binary log

create...

binary log

Client

create...

Table t Table t

create...

binary log

create...

binary log

Client

create...insert...

Table t Table t

create...

binary log

create...

binary log

Client

create...insert...

Table t1

Table t

create...

binary log

create...insert...A

binary log

Client

create...insert...

Table t1

create...insert...B

binary log

create...insert...A

binary log

Client

Actually, Transactions Land in Slave's Relay Log

binary logrelay log

binary log

Client

create...

binary logrelay log

binary log

Client

create...

binary logrelay log

create...

binary log

Client

Table t

create...

binary log

create...

relay log

create...

binary log

Client

Table t

create...

binary log

create...

relay log

create...

binary log

Client

Table t Table t

create...

Replication is Asynchronous

create...

binary log

create...

relay log

create...

binary log

Client

Table t Table tTransactionapplied here

andcopied here

THENapplied here

THENack'ed

create...insert...

create...

binary log

create...

relay log

create...

binary log

Client

andcopied here

THENapplied here

THENack'ed

create...insert...

create...

binary log

create...

relay log

create...insert...A

binary log

Client

Table t1

Table tTransactionapplied here

andcopied here

THENapplied here

THENack'ed

create...insert...

create...

binary log

create...

relay log

create...insert...A

binary log

Client

Table t1

andcopied here

THENapplied here

THENack'ed

create...insert...

create...

binary log

create...insert...

relay log

create...insert...A

binary log

Client

Table t1

andcopied here

THENapplied here

THENack'ed

create...insert...

create...insert...B

binary log

create...insert...

relay log

create...insert...A

binary log

Client

Table t1

Table t1Transaction

applied hereand

copied hereTHEN

applied hereTHENack'ed

Next steps

What isSemi-Synchronous

Replication?

Asynchronous vs Semi-sync Replication

By default, replication is asynchronous● In parallel: Master acks to app and sends transaction to slave

● Fast● Changes lost if master dies

MySQL 5.5: semi-synchronous replication possible● In sequence: slave receives transaction, then master acks to app

● Slower: Master waits for slave● Less risk for lost updates

create...

Semi-Synchronous Replication (MySQL 5.5)

create...

binary log

create...

relay log

create...

binary log

Client

THENcopied here

andapplied here

THENack'ed

create...insert...

create...

binary log

create...

relay log

create...

binary log

Client

andapplied here

THENcopied here

THENack'ed

create...insert...

create...

binary log

create...

relay log

create...insert...A

binary log

Client

Table t1

andapplied here

THENcopied here

THENack'ed

create...insert...

create...

binary log

create...insert...

relay log

create...insert...A

binary log

Client

Table t1

andapplied here

THENcopied here

THENack'ed

create...insert...

create...

binary log

create...insert...

relay log

create...insert...A

binary log

Client

Table t1

andapplied here

THENcopied here

THENack'ed

create...insert...

create...

binary log

create...insert...

relay log

create...insert...A

binary log

Client

Table t1

andapplied here

THENcopied here

THENack'ed

Slave tells masterwhen to ack!

create...insert...

create...insert...B

binary log

create...insert...

relay log

create...insert...A

binary log

Client

Table t1

Table t1Transaction

applied hereand

applied hereTHEN

copied hereTHENack'ed

What's New inSemi-Synchronous

Replication?

Loss-Less Semi-Sync Replication (MySQL 5.7.2)

MySQL 5.5:semi-synchronous replication● Master commit● Slave receive● Client ack

.If master crashesbetween 1 and 2,committed data is lost

.Concurrent clientsmay have seen the transaction

MySQL 5.7.2:loss-less semi-sync replication● Slave receive● Master commit● Client ack

.If master crashes, all committed data is on slave

create...

binary log

create...

relay log

create...

binary log

Client

Table t Table tTHEN com-mitted here

andapplied here

Transactioncopied here

andack'ed

create...insert...

create...

binary log

create...

relay log

create...

binary log

Client

Table t Table tTHEN com-mitted here

andapplied here

andack'ed

create...insert...

create...

binary log

create...insert...

relay log

create...insert...A

binary log

Client

Table t Table tand

applied hereTHEN com-mitted here

andack'ed

create...insert...

create...

binary log

create...insert...

relay log

create...insert...A

binary log

Client

Table t1

Table tand

applied here

andack'ed

THEN com-mitted here

create...insert...

create...

binary log

create...insert...

relay log

create...insert...A

binary log

Client

Table t1

Table tand

applied here

Slave tells masterwhen to commit!

andack'ed

THEN com-mitted here

create...insert...

create...

binary log

create...insert...

relay log

create...insert...A

binary log

Client

Table t1

Table tand

andack'ed

create...insert...

create...insert...B

binary log

create...insert...

relay log

create...insert...A

binary log

Client

Table t1

Table t1and

andack'ed

Summary● MySQL 5.7.2: loss-less semi-synchronous replication possible● If master crashes, all committed data is on slave● To enable:

master> SET GLOBAL rpl_semi_sync_master_wait_point = AFTER_SYNC;

● (default: AFTER_COMMIT – for 5.5 behavior)

Next steps

What isMulti-Threaded

Slave?

binary log

Before MySQL 5.6: Single-threaded slave

Improved Multi-Threaded Slave

relay logClient

Client

binary log

relay log

Transactionsapplied

in parallel

Client

Transactionslogged

in sequence

Transactionsapplied

in sequence

binary log

relay log

Transactionsapplied

in parallel

Client

Transactionslogged

in sequence

Transactionsapplied

in sequence

Bottleneck!

binary log

MySQL 5.6: Multi-threaded slave by database

relay log

Transactionsapplied

in parallel

Client

Transactionslogged

in sequence

Transactionsapplied

in parallel

binary log

MySQL 5.6: Multi-threaded slave by database● Different databases go to different threads

relay logClient

Client

binary log

MySQL 5.6: Multi-threaded slave by database● Different databases go to different threads● Great for some applications, BUT:

● No improvement if there is only one database● May break cross-database consistency

relay logClient

Client

What's New inMulti-Threaded

Slave?

binary log

MySQL 5.7.2: Multi-threaded slave by master concurrency● Transactions that were prepared at the same time on master

cannot conflict● Master stores a logical timestamp in the binary log● Slave applies transactions with same timestamp in parallel

relay logClient

Client

binary log

MySQL 5.7.2: Multi-threaded slave by master concurrency● Works always

● Even for one-database applications● Consistent

relay logClient

Client

binary log

MySQL 5.7.2: Multi-threaded slave by master concurrency● To enable:

slave> SET GLOBAL slave_parallel_type = logical_clock;

(default: database – for 5.6 behavior)

relay logClient

Client

Next steps

Multi-Source Replication

What isMulti-SourceReplication?

Before: Slave can have one master Labs release: Slave can have multiple masters

Note● No conflict detection/resolution● Not update everywhere● Not synchronous

The masters must have conflict-free workloads!

Slave can have multiple masters

Preview release: labs.mysql.com● Not for production yet● Known and unknown limitations and bugs● Try it out and give feedback!

Why UseMulti-SourceReplication?

Multi-Source Replicationfor Data Analytics

Business IntelligenceData analytics

Backupetc

Database 2

Database 3

Database 1

SDatabase 1, 2, 3

Multi-Source Replicationfor Merging Shards

Shard 2

Shard 1

SNew Shard

How DoesMulti-Source

relay log

Multi-Source + Multi-Threaded

relay log

Channel = Full slave pipeline

relay log

Channel = Full slave pipeline

Channels are named

my_channel

another_channel

third_channel

Setting up CHANGE MASTER TO […] FOR CHANNEL = 'name'

Other replication commands: START SLAVE […] FOR CHANNEL = 'name' STOP SLAVE […] FOR CHANNEL = 'name' RESET SLAVE […] FOR CHANNEL = 'name' FLUSH RELAY LOGS FOR CHANNEL = 'name' SHOW RELAY LOG EVENTS FOR CHANNEL = 'name'

START SLAVE […] FOR ALL CHANNELS STOP SLAVE […] FOR ALL CHANNELS RESET SLAVE […] FOR ALL CHANNELS

SELECT MASTER_POS_WAIT('file', pos[, timeout][, 'channel'])

Compatibility CHANGE MASTER TO […] (with no channel specified) START SLAVE […] (with no channel specified) etc

… are the same as …

CHANGE MASTER TO […] FOR CHANNEL = '' START SLAVE […] FOR CHANNEL = '' etc

Next steps

Monitoring with Performance_Schema

Traditional replication monitoring:SHOW SLAVE STATUS;

– Simple

– Not SQL friendly – no WHERE, no joins, etc

– Multi-source has per-source status

– Multi-threaded slave has per-applier status

5.7.2: Performance_Schema tables for replication slave

relay log

execute statusby coordinator

execute statusby worker

executeconfiguration

executestatus

connectionconfiguration

connectionstatus

6 tables in performance_schema database:

replication_connection_configuration

replication_connection_status

replication_execute_configuration

replication_execute_status

replication_execute_status_by_coordinator

replication_execute_status_by_worker Consistent semantics across tables Consistent naming across tables

One row for each workerin each multi-source channel

One rowfor each

multi-sourcechannel

Example: Connection statusmysql> select * from performance_schema.replication_connection_status\G*************************** 1. row *************************** CHANNEL_NAME: CHANNEL1 SOURCE_UUID: 7cff740623ca11e3ac3e5c260a83b12b THREAD_ID: 13 SERVICE_STATE: ONRECEIVED_TRANSACTION_SET: 7cff740623ca11e3ac3e5c260a83b12b:14 LAST_ERROR_NUMBER: 0 LAST_ERROR_MESSAGE: LAST_ERROR_TIMESTAMP: 00000000 00:00:00*************************** 2. row *************************** CHANNEL_NAME: CHANNEL2

⋮ One row for each channel

⋮ The master's server_uuid

⋮ Thread id and status

⋮ Set of transactionsreceived through this channel

⋮ Error status

Example: Connection statusmysql> select * from performance_schema.replication_connection_status\G*************************** 1. row *************************** CHANNEL_NAME: CHANNEL1 SOURCE_UUID: 7cff740623ca11e3ac3e5c260a83b12b THREAD_ID: NULL SERVICE_STATE: OFFRECEIVED_TRANSACTION_SET: 7cff740623ca11e3ac3e5c260a83b12b:14 LAST_ERROR_NUMBER: 1045 LAST_ERROR_MESSAGE: error connecting to master 'me@host:13000' … LAST_ERROR_TIMESTAMP: 20131109 21:03:23*************************** 2. row *************************** CHANNEL_NAME: CHANNEL2

Error status

Example: Connection statusmysql> select * from performance_schema.replication_connection_status\G*************************** 1. row *************************** CHANNEL_NAME: CHANNEL1 SOURCE_UUID: 7cff740623ca11e3ac3e5c260a83b12b THREAD_ID: NULL SERVICE_STATE: OFFRECEIVED_TRANSACTION_SET: 7cff740623ca11e3ac3e5c260a83b12b:14 LAST_ERROR_NUMBER: 1045 LAST_ERROR_MESSAGE: error connecting to master 'me@host:13000' … LAST_ERROR_TIMESTAMP: 20131109 21:03:23*************************** 2. row *************************** CHANNEL_NAME: CHANNEL2

Thread stoppedon error

Next steps

Try it out!● MySQL 5.6:

http://dev.mysql.com/downloads/mysql/● MySQL 5.7.4:

http://dev.mysql.com/downloads/mysql/5.7.html● Labs release:

http://labs.mysql.com

Read the manual!● http://dev.mysql.com/doc/refman/5.7/en/index.html

Next Steps

Send us feedback!● Shivji Kumar Jha

shivji.jha@oracle.com● Sven Sandberg

sven.sandberg@oracle.com● Luís Soares

luis.soares@oracle.com

File bugs!● http://bugs.mysql.com

Next Steps

MySQL Developer Day conference: MySQL Replication and Scalability

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