con5409_jadhav-yahoo case study- mysql gtids and parallel or multithreaded replication

8/17/2019 CON5409_Jadhav-Yahoo Case Study- MySQL GTIDs and Parallel or Multithreaded Replication

1/57

Yahoo Case Study: MySQL GTIDs and Parallel orMultithreaded Replication

PRESENTED BY Stacy Yuan, Yashada Jadhav October 2015


2/57

About Yahoo

! Yahoo is focused on making the world’s daily habits inspiring and

entertaining.

! By creating highly personalized experiences for our users, we keep people

connected to what matters most to them, across devices and around theworld.

! In turn, we create value for advertisers by connecting them with the

audiences that build their businesses

! More than 1B monthly active users across Yahoo and Tumblr

!

More than 575M mobile monthly active users across Yahoo and Tumblr

Yahoo Case Study: MySQL GTIDs and Parallel orMultithreaded Replication


3/57

Ad Products Team

Mission Statement: Delivering scalable and cost efficient data services

through innovation and automation powering Yahoo Products

! Thousands of Production Servers

! OLTP systems & Data marts

! Database Design and Architecture

! Capacity Planning and Performance Reviews

! 24x7 Monitoring and Operational Support


4/57

MySQL at Yahoo

! MySQL powers many mission-critical products within Advertisingand User space across Desktop and Mobile

! Multiple production configurations based on product requirement

!

DBaaS setup for multiple products! Yahoo Sports: Mobile friendly

! Flickr: Sharded across thousands of servers

! Hot:Hot, Hot:Warm Configurations

! Versions range from Percona Server 5.1 to 5.6 including PerconaXtraDB Cluster

! Operating systems running customized RHEL 5.6 to 6.5


5/57

About Stacy

! Senior MySQL database administrator

! 10+ years of experience on various flavors of relational databases.

! Focus on performance tuning, code reviews, database deployment

and infrastructure management for MySQL! In her spare time, she enjoys reading books and doing some

volunteer work.


6/57

About Yashada

! MySQL DevOps Engineer with a background in database designand performance tuning.

! 4+ years of experience on various flavors of relational databases.

!

In her spare time, she enjoys listening to music and going toconcerts. She appreciates sarcasm a lot too!


7/57

What are the next 45 minutes about?

! GTID Replication! Advantages and Disadvantages! Performance when compared to regular replication

! Multi threaded slaves! Why do we want MTS?!

MTS vs single threaded replication - Performance tests

! Rolling out GTID and MTS to a live system with no downtime

! GTID and MTS in Production!

Operational issues! Monitoring and HA! Backups using xtrabackup


8/57

Why go for GTID and MTS

! Slave promotion becomes easier with a global transaction ID

! Multitenant database systems suffer from problems like resource

contention due to bad queries, batch jobs etc. that affect replication.

! MTS without GTID - replication co-ordinates might no longer beaccurate due to multiple parallel worker threads.

!

MTS with GTID


9/57

GTID Replication


10/57

File-based Replication

Enables data from one MySQL database server (the master) to bereplicated to one or more MySQL database servers (the slaves) throughMySQL log file and its position

! Needs replication user, binlog is enabled!

Needs a copy of master database! Connect to master through master_host, port, replication user,

master log file and its position.! Each slave pulls the data from the master, and execute the events

to the slave.


11/57

GTID Replication

A global transaction identifier (GTID) is a unique identifier created andassociated with each transaction committed on the server of origin(master).

GTID is unique not only to the server on which it originated, but isunique across all servers in a given replication setup.

GTID = source_id :transaction_id

! The source_id identifies the originating server.!

The transaction_id is a sequence number determined by the order inwhich the transaction was committed on this server.

Example:! 5c7401d3-3623-11e5-ae8c-78e7d15fd641:1-13476


12/57

GTID Replication Advantage

! Replication topology is easy to change - binlog file name andposition are not required any more instead we usemaster_auto_position=1

! Failover is simplified

!

Increase performance in relay slave - set sync_binlog=0

! Managing multi-tiered replication is easier

Master_log_file=‘mysql-bin.***’Master_log_pos=****

master_auto_position=1


13/57

Replication Failover Comparison

Regular Rep FailoverIf S1 is bad, S4S5 needto be rebuilt.

M M

GTID Rep FailoverRedirectS4 to M

S2

S3

S1

S4

S5

S2 S1

S3 S4

S5


14/57

GTID Replication Limitations

! GTID does not provide replication monitoring

! SQL_SKIP_SLAVE_COUNTER does not work

! Can not force the database to start replication from specific position


15/57

GTIDs Replication Caveats

! Updates involving non-transactional storage engines.

! CREATE TABLE ... SELECT statements is not supported.

! Temporary table is not supported inside a transaction

To prevent GTID-based replication to fail: enforce-gtid-consistency


16/57

Replication Performance GTID vs Regular Rep

In terms of performance, GTID is almost same as regular replication. Itis slightly slower.

The reasons could be -

!

GTIDs write more lines into binary log - information about GTID! GTID performs additional checks for transactions


17/57

GTID vs Regular Replication


18/57



19/57



20/57

Multi threaded Replication


21/57

Replication Performance Issue

! Multi threaded applications write to the master in a parallel fashion

! But the replication from master to slave is single thread, it becomesbottleneck in a busy system.

Master Slave


22/57

Multi-Threaded Slaves (MTS)

! Type of thread – Coordinator thread and Worker thread! Coordinator thread on slave dispatches work across several worker

threads! Each worker thread commit transaction individually.! Multiple active schemas/databases can take advantage of parallel

replication

Master Slave


23/57

MTS Prerequisites

! MySQL 5.6 above! Transactions are independently based on different databases.! Multitenant databases is the best to enable MTS! N databases, use N parallel workers

slave_parallel_workers = N

! Example: 3 databases in MySQL, better to setslave_parallel_workers =3

Masterdb1, db2, db3

Slavedb1, db2, db3


24/57

Configure MTS

!

STOP SLAVE;! SET GLOBAL slave_parallel_workers=3;! START SLAVE;


25/57

MTS Execution Gaps and Checkpoint

!

Events are no longer guaranteed to be consecutive

! Execution gaps are tracked

! Checkpoints are performed from time to time

Check settingsslave_checkpoint_period default 300 msslave_checkpoint_group default 512 trx

! Exec_Master_Log_Pos shows the latest checkpoint and not latest

transaction

! How to fix execution gaps -STOP SLAVE; START SLAVE UNTIL SQL_AFTER_MTS_GAPS


26/57

Convert MTS to Single-threaded

!

Run MTS until no more gaps are found in the relay log

! Stop Replication

! Configure single threaded slave

! Start single threaded slave

START SLAVE UNTIL SQL_AFTER_MTS_GAPS;

SET @@GLOBAL.slave_parallel_workers = 0;

START SLAVE;


27/57

MTS Advantages and Limitations

Advantages:

! Take advantage of multi-core servers

! Changes to each schema applied and committed independently by

worker threads! Smaller risk of data loss

Limitations:

! START SLAVE UNTIL no longer support

! Foreign Keys cross-referencing DBs will disable MTS

! No implicit transaction retry after transient failure


28/57

MTS Caveats

! Enforcing foreign key relationships between tables in differentdatabases causes MTS to use sequential mode which can havenegative impact on performance

!

Single database replication, it slows down the replicationperformance


29/57

MTS without GTID

!

Exec_Master_Log_Pos in SHOW SLAVE STATUS is misleading.

! Skipping replication errors with SQL_SLAVE_SKIP_COUNTER=1 isdangerous

! Backup from slave, either mysqldump and xtrabackup might not getright position

GTID comes to the rescue


30/57

Performance Testing - GTID with MTS Setup

Test scenario:! one master,! two slaves (one is single-threaded replication, another slave is multi-

threaded replication both using GTID

Master

Slave1 Slave2

GTID Rep MTS GTID Rep


31/57

Replication Performance Comparison


32/57

Replication Performance ComparisonQPS is increased about 3 or 4 timesLoad, CPU, and Writes per second are increased as well


33/57

Replication Performance Comparison


34/57

GTID with MTS enabled: Things to watch out for

!

Exec_Master_Log_Pos is no longer reliable! Executed_Gtid_Set is the reliable

! SQL_SLAVE_SKIP_COUNTER no longer works

! START SLAVE UNTIL is not supported

!

Slave_transaction_retries is treated as 0, and can not be changed.


35/57

Rolling out GTID and MTS to production


36/57

Online Rollout GTID with MTS in Percona Server

!

MySQL56 requires downtime to enable GTID, it is not acceptable

! With Percona server 5.6, with almost no downtimeThe variable GTID_DEPLOYMENT_STEP plays an important role


37/57

Database Servers Setup

Dual masters setup ! Masters setup cross different colos.

! Each master carries one slave DNS

Prod master BCP master

Prod slave BCP slave


38/57

Enable GTID without downtime

Enable GTID in BCP side

1. Make sure BCP master andBCP slave are sync

2. Stop mysqld in BCP master and BCP slave,

add gtid_deployment_step=on,

gtid_mode=ON ,

enforce-gtid-consistency into my.cnf

Restart mysqld in both servers.

3. Replication from prod master to

BCP master is good.

DNS

Prod master

BCP master GTID_deployme

nt_step=on

Prod slave

BCP slaveGTID_deployme

nt_step=on


39/57


Promote BCP master to Prod master

4. Prod master: set global read_only=on

5. BCP master:

set global gtid_deployment_step = off;

set global read_only=off;

6. The replication from BCP master to

Prod master is broken.

DNS

Prod master

BCP masterGTID_deployme

nt_step=off

Prod slave


nt_step=on


40/57


Enable GTID in Prod master

7. Enable GTID on old prod master and prod slave

8. Fix replication from BCP master to prod master

CHANGE MASTER TO

MASTER_AUTO_POSITION = 1;

START SLAVE;

9. Enable GTID replication from

Prod master to BCP master

10. Enable MTS in all serversstop slave;

set global slave_parallel_workers=16;start slave;

DNS

Prod masterGTID enabled


nt_step=off

Prod slaveGTID enabled


nt_step=on


41/57


Switch back

10. Perform switchover in Prod master

Disable gtid_deployment_step across all servers.DNS

Prod masterGTID enabled


nt_step=off

Prod slaveGTID enabled


nt_step=off


42/57

Switchover Steps

•

Enable global read_only=on in prod master

•

Sanity check to make sure BCP master catch up its master(WAIT_UNTIL_SQL_THREAD_AFTER_GTIDS)

•

Disable read_only in BCP master. BCP master becomes prodmaster

Failover:

•

If prod master is unreachable, it will be failover without step 1 and 2.


43/57

GTID and MTS in Production : MySQL Ops


44/57

GTID and MTS in production : What did we learn?

!

Errant Transactions

! Replication Monitoring

!

Building slaves using xtrabackup


45/57

Errant Transaction

The errant transactions are:They are only executed in slaves.

! Could result from a mistake

!

Could be intentionally by design, such as report tables

! Why they cause problem

When the slave becomes the master during failover, it exchanges its ownset of executed GTIDs, then send any missing transactions to the slaves.


46/57

Errant Transaction Detection and Fix

Detect: GTID_SUBSET(slave-Executed_Gtid_Set, master-Executed_Gtid_Set)

If it returns true(1), no errant trx.

If it returns false(0), it does have errant trx.

Identify:GTID_SUBTRACT(slave-Executed_Gtid_Set, master-Executed_Gtid_Set)It returns the errant GTID.

Fix: Inject empty transaction on all other servers.

If the transaction must be executed in slave only, useset sql_log_bin=0;


47/57

Inject Empty Transaction

Sql_skip_slave_counter=n no longer works

Execute a fake trx with the GTID that you want to skip

For example: GTID=68fb0071-299b-11e5-9cd6-78e7d15dbe38:501

STOP SLAVE;SET GTID_NEXT="68fb0071-299b-11e5-9cd6-78e7d15dbe38:501";BEGIN; COMMIT;SET GTID_NEXT="AUTOMATIC";START SLAVE;

SHOW SLAVE STATUS\G # Verification


48/57

MySQL Replication Monitoring

•

Seconds_Behind_Master

A good approximation of how late the slave is only when the slaveactively processes updates.

If the network is slow or not much updates in the master, this is NOTa good measurement.


49/57

MySQL Replication Monitoring at Yahoo

!

MySQL Health Heartbeat

1. Master generates heartbeat by updating timestamp (last_update)

2. Slave checks the difference between current time and last_update


50/57

GTID MTS Monitoring Challenger

! SHOW SLAVE STATUS

! Seconds_Behind_Master is still a good indication of thereplication lag

! Retrieved_Gtid_Set: List of GTIDs received by the I/O thread,cleared after a server restart

! Executed_Gtid_Set: List of GTIDs executed by the SQL thread

!

Auto_position: 1 if GTID-based replication is enabled

! 5.7 is using performance_schema


51/57

Build Slaves Using Xtrabackup

! Start Xtrabackup from either master or slave

If the backup is taken from the master,

Please check the file xtrabackup_binlog_info in the backup folder

If the backup is from slave,

Please check the file xtrabackup_slave_info

$ cat xtrabackup_slave_info

SET GLOBAL gtid_purged='ffee1ff8-363f-11e5-af47-9cb654954cac:1-29123533';

CHANGE MASTER TO MASTER_AUTO_POSITION=1


52/57

Build Slave Using Xtrabackup

Enable Replication in Slave

Issuemysql> SET GLOBAL gtid_purged='ffee1ff8-363f-11e5-af47-9cb654954cac:1-29123533';

ERROR 1840 (HY000): @@GLOBAL.GTID_PURGED can only be set when@@GLOBAL.GTID_EXECUTED is empty.

How to fix

! RESET MASTER;

! SET GLOBAL gtid_purged='ffee1ff8-363f-11e5-af47-9cb654954cac:1-29123533’;

! CHANGE MASTER TO MASTER_HOST="mastername", master_user='rep_user',master_password='rep_password', MASTER_AUTO_POSITION = 1;

! START SLAVE;


53/57

Build Slave Using Xtrabackup

Still issue?

mysql> start slave;ERROR 1872 (HY000): Slave failed to initialize relay log info structure from the repository

RESET SLAVE;

START SLAVE;


54/57

Summary

! GTID

! MTS

! GTID with MTS performance comparison

!

GTID with MTS online rollout! Things to watch out

! Rebuild slave


55/57

We would love to talk more ..

http://mysqlatyahoo.tumblr.com

YJ

[email protected]

https://www.linkedin.com/pub/yashada-jadhav/18/659/a6

Stacy Yuan

[email protected]

https://www.linkedin.com/pub/stacy-yuan/53/577/324


56/57

Appendix


57/57

Appendix: 1. GTID with MTS Configuration and Setup

! Hardware: 24 CPUs, 48 GB memory

! Database: innodb_buffer_pool_size = 32 GB

innodb_log_file_size = 1G

innodb_thread_concurrency = 0Case1:

! Master: Create 8 schemas and 8 users, each user access oneschema

Create 8 tables and 1 million rows in each table for each schema

!

Eight sysbench run executed concurrently on the master.

num-threads=2

max-time=900

oltp-read-only=off

con5409_jadhav-yahoo case study- mysql gtids and parallel or multithreaded replication

Documents