replication tips & trick for smug

Copyright © 2012, Oracle and/or its affiliates. All rights reserved. Insert Information Protection Policy Classification from Slide 121

Replication Tips & TricksMats [email protected]

+ some things about GTIDs

2 Copyright © 2012, Oracle and/or its affiliates. All rights reserved.

Program Agenda

Replication setup and status checking

Slave fail-over using GTID

Binary log analysis

Crash-safe slaves

Multi-source replication


About the Presentation

This presentation will introduce you to some replication features and also briefly show tips and tricks on how to work with replication. The focus is on short ideas and each item does not go deeper into details.


What is Replication?

● MySQL Master Server

– Changes data– Sends changes to slave

● MySQL Slave Server

– Receives changes from master– Applies received changes to

database


Replication Topologies

TreeSimple

CircularDual Master


Why Replication?Scaling out

Reads

Writes


Why Replication?Redundancy

CrashSlave

Promotion

New Master


Replication Architecture

Master Slave


Reading Slave Status

● I/O Thread Status

– Slave_IO_Running

– Last_IO_Errno

– Last_IO_Error

– Last_IO_Error_Timestamp

● SQL Thread Status

– Slave_SQL_Running

– Last_SQL_Errno

– Last_SQL_Error

– Last_SQL_Error_Timestamp

● Master being replicated from

– Master_Host

– Master_Port

Understanding the fields of SHOW SLAVE STATUS


Reading Slave Status

● Next event to execute – in master log coordinates

– Relay_Master_Log_File + Exec_Master_Log_Pos

● Next event to execute – in relay log coordinates

Relay_Log_File + Relay_Log_Pos

● Next event to read from master

Master_Log_File + Read_Master_Log_Pos

Understanding the fields of SHOW SLAVE STATUS


Reading the Binary Log

● Use mysqlbinlog

--hexdump Show hex dump of event as comment

--start-position Start dumping at a position

--stop-position Stop dumping after this position

# at 275#120927 23:11:58 server id 3 end_log_pos 373 # Position Timestamp Type Master ID Size Master Pos Flags # 113 1e c1 64 50 02 03 00 00 00 62 00 00 00 75 01 00 00 00 00

Query Little-endian

17516=37310

Decoding the binary log



# at 275#120927 23:11:58 server id 3 end_log_pos 373 # Position Timestamp Type Master ID Size Master Pos Flags # 113 1e c1 64 50 02 03 00 00 00 62 00 00 00 75 01 00 00 00 00# 126 c5 03 00 00 00 00 00 00 04 00 00 1a 00 00 00 00 |................|# 136 00 00 01 00 00 00 00 00 00 00 00 06 03 73 74 64 |.............std|# 146 04 21 00 21 00 08 00 74 65 73 74 00 69 6e 73 65 |.......test.inse|# 156 72 74 20 69 6e 74 6f 20 74 32 20 76 61 6c 75 65 |rt.into.t2.value|# 166 73 20 28 31 2c 27 74 65 73 74 69 6e 67 27 29 |s..1..testing..|# Query thread_id=965 exec_time=0 error_code=0SET TIMESTAMP=1348780318/*!*/;insert into t2 values (1,'testing')/*!*/;

Decoding the binary log



● Use mysqlbinlog

--verbose Decode row events into pseudo-SQL

# at 849# at 893#120928 15:19:24 server id 3 end_log_pos 893 Table_map: `test`.`t2` mapped to number 48#120928 15:19:24 server id 3 end_log_pos 941 Write_rows: table id 48 flags: STMT_END_F

BINLOG '3KNlUBMDAAAALAAAAH0DAAAAADAAAAAAAAEABHRlc3QAAnQyAAIDDwIoAAM=3KNlUBcDAAAAMAAAAK0DAAAAADAAAAAAAAEAAv/8AwAAAA1yb3dzIGFyZSBjb29s'/*!*/;

Decode row events



● Use mysqlbinlog

--verbose Decode row events into pseudo-SQL

# at 849# at 893#120928 15:19:24 server id 3 end_log_pos 893 Table_map: `test`.`t2` mapped to number 48#120928 15:19:24 server id 3 end_log_pos 941 Write_rows: table id 48 flags: STMT_END_F

BINLOG '3KNlUBMDAAAALAAAAH0DAAAAADAAAAAAAAEABHRlc3QAAnQyAAIDDwIoAAM=3KNlUBcDAAAAMAAAAK0DAAAAADAAAAAAAAEAAv/8AwAAAA1yb3dzIGFyZSBjb29s'/*!*/;### INSERT INTO test.t2### SET### @1=3### @2='rows are cool'

Decode row events


CHANGE MASTER TO MASTER_HOST='master1.example.com', MASTER_PORT=3306, MASTER_USER='repl_user', MASTER_PASSWORD='xyzzy', MASTER_LOG_FILE='master-bin.00001', MASTER_LOG_POS=22145;

Global Transaction Identifiers (GTIDs)

● Binary log positions manually handled

● Each server has it's own position

● Failing over slaves to new masters difficult

– What is the position to fail over to?

Handling positions in MySQL 5.5

Different fordifferent servers



● MySQL 5.6 has Global Transaction ID

– Positions independent of server● GTID handshake

– Done on connection with master– Negotiate position automatically

CHANGE MASTER TO MASTER_HOST='master1.example.com', MASTER_PORT=3306, MASTER_USER='repl_user', MASTER_PASSWORD='xyzzy', MASTER_LOG_FILE='master-bin.00001', MASTER_LOG_POS=22145; MASTER_AUTO_POSITION=1;

Enabling Global Transaction IDs



● Turn on GTIDs

● Turn off dangerous statements

– CREATE TABLE...SELECT– CREATE TEMPORARY TABLE

● Inside transactions

CHANGE MASTER TO MASTER_HOST='master1.example.com', MASTER_PORT=3306, MASTER_USER='repl_user', MASTER_PASSWORD='xyzzy', MASTER_LOG_FILE='master-bin.00001', MASTER_LOG_POS=22145; MASTER_AUTO_POSITION=1;

Enabling Global Transaction IDs

[mysqld]…gtid-mode=onenforcegtidconsistency=onlog-bin=master-binlog-slave-updates



● Global transaction ID

– A server UUID + Transaction Number

a61678ba488942799e5845ba840af334:1

– Preserved when replicated● Global Transaction ID Set

– Sequence of Server UUID + Transaction Number Range

a61678ba488942799e5845ba840af334:15,f88e2a43a13e11e298de0021cc6850ca:122564

Global Transaction ID Concepts



● @@GTID_EXECUTED

– GTID set of all transactions logged in the binary log

● @@GTID_PURGED

– GTID set of all transaction purged from binary log– Cannot be sent to slaves

Server Variables


Cloning a Slave

1. Stop the slave

2. Write down where slave has stopped

– SHOW SLAVE STATUS– Relay_Master_Log_File + Exec_Master_Log_Pos

3. Backup slave

– mysqldump – slow but safe

dumpslave Generate CHANGE MASTER

– Physical file copy – fast but you need to shut down the server

Creating a slave image

BeforeMySQL 5.6


Cloning a Slave

4. Restore backup on new slave

5. Direct the slave to the master

– CHANGE MASTER– Master_Host + Master_Port– Relay_Master_Log_File + Exec_Master_Log_Pos

6. Start slave

– START SLAVE

Setting up the new slave

BeforeMySQL 5.6


Cloning a Slave

1. Stop the slave

2. Backup slave

mysqldump host=slave1.example.com user=root \ dumpslave setgtidpurged >image.sql

3. Start the slave

4. Restore image on new slave

mysql host=slave2.example.com user=root <image.sql

5. Start Slave

MySQL 5.6or later

Tell slave that transactionsin image cannot be replicated


Point in time recovery

● Use mysqlbinlog

--to-datetime Stop reading when reaching date● Example

mysqlbinlog --read-from-remote-server \ --host=master -uroot --position=192 \

--to-datetime=”2009-04-11 12:36:56” \master-bin.00002[2-4] |

mysql -uroot --host=slave

Warning

: times

tamps

are

not mo

notonic

ally inc

reasing

!


Using Relay Servers

● Relieve master server by creating relay slaves

● Just keep binary logs

● Do not store data in tables

– Use BLACKHOLE engine– --log-slave-updates

SET STORAGE_ENGINE = BLACKHOLEALTER TABLE table ENGINE = BLACKHOLE


Using Relay Servers

● Filtering replication stream

● Filtering done on relay servers

● replicatewild*table

– Work with cross-database queries

replicate-wild-do-table=*.%_east replicate-wild-do-table=*.%_west


Write Your Own Library

● Create a utility library to easier work with replication

● Common functions to manage replication:

– Start/stop slave– Change master– Fetch master position– Fetch slave execute/read position– Fetch master host information

Write your own utility library



# Usage: mysql_exec socket sql ... mysql_exec () { sock=$1 shift 1 mysql uroot vertical batch \ skipcolumnnames \ socket="$sock" \ exec "$*"}

# Usage: stop_slave socket [ thread ]stop_slave () { mysql_exec $1 STOP SLAVE $2}

# Usage: start_slave socket [ thread ]start_slave () { mysql_exec $1 START SLAVE $2}

Basic functions using Bourne shell



# Usage: change_master socket [ host [ port [ file [ pos ] ] ] ]change_master () { host=${2:+MASTER_HOST=\'$2\'} port=${3:+,MASTER_PORT=$3} file=${4:+,MASTER_LOG_FILE=\'$4\'} pos=${5:+,MASTER_LOG_POS=$5} mysql_exec $1 CHANGE MASTER TO $host $port $file $pos}

# Usage: fetch_master_pos socketfetch_master_pos () { mysql_exec $1 SHOW MASTER STATUS | grep '\<File\|\<Pos' | cut f2 d:}




# Usage: fetch_slave_exec_pos socketfetch_slave_exec_pos () { mysql_exec $1 SHOW SLAVE STATUS | grep '\<Relay_Master_Log_File\|\<Exec_Master_Log_Pos' | cut f2 d:}

# Usage: fetch_slave_read_pos socketfetch_slave_read_pos () { mysql_exec $1 SHOW SLAVE STATUS | grep '\<Master_Log_File\|\<Read_Master_Log_Pos' | cut f2 d:}



Round-Robin Replication

● Slave can only replicate from single master at a time

● Use time sharing to replicate from several masters

Switcher

master1.example.com master2.example.com

slave1.example.com

Stop

Save

Restore

Start


# Usage: fetch_host_and_pos socketfetch_host_and_pos () { mysql_exec $1 SHOW SLAVE STATUS | grep '\<Master_$Host\|Port\|Log_File$\|\<Read_Master_Log_Pos' | cut -f2 -d:}

# Usage: stop_and_save socketstop_and_save () { sock="/var/run/mysqld/$1.sock" stop_slave $socket fetch_host_and_pos $sock >$1.savepos}


A version using Bourne Shell


restore_and_start () { socket="/var/run/mysqld/$1.sock" cat $1.savepos | { read host read port read file read pos change_master $socket \ $host $port $file $pos start_slave $socket }}


cnt=1

while truedo stop_and_save mysqld.$cnt cnt=`expr $cnt % 5 + 1` restore_and_start mysqld.$cnt sleep 60done

A version using Bourne Shell


Crash-safe Slaves

● Traditional Replication

– Position stored in file– Update after transaction– Crash can lose update

● Transactional Replication

– Positions stored in table– Update part of transaction– Crash-safe

● Repository location FILE or TABLE

master_info_repositoryrelay_log_info_repository

FILE TABLE

Keeping replication information in sync with data


Crash-safe Slaves

● Direct server to use table-based repository

– Defaults to FILE

master_info_repository=TABLErelay_log_info_repository=TABLE

● Ensure that a transactional engine is used

– InnoDB default since 5.6.6– Before 5.6.6: set the storage engine

ALTER TABLE slave_master_info ENGINE = InnoDBALTER TABLE slave_relay_log_info ENGINE = InnoDB

Steps to set up crash-safe slaves


CREATE TABLE current_master ( idx INT) ENGINE=InnoDB

CREATE TABLE my_masters ( idx INT PRIMARY KEY, host CHAR(50) NOT NULL, port INT NOT NULL DEFAULT 3306, log_file CHAR(50), log_pos LONG, UNIQUE INDEX (host,port,user)) ENGINE=InnoDB


CREATE PROCEDURE save_position()BEGIN DECLARE l_idx INT UNSIGNED;

UPDATE my_masters AS mi, mysql.slave_relay_log_info AS rli SET mi.log_pos = rli.master_log_pos, mi.log_file = rli.master_log_name WHERE idx = (SELECT idx FROM current_master);END

A version using pure SQL



In pure SQL

CREATE PROCEDURE fetch_next_master(OUT p_host CHAR(50), OUT p_port INT UNSIGNED, OUT p_file CHAR(50), OUT p_pos BIGINT)BEGIN DECLARE l_next_idx INT DEFAULT 1;

SELECT idx INTO l_next_idx FROM my_masters WHERE idx > (SELECT idx FROM current_master) ORDER BY idx LIMIT 1;

SELECT idx INTO l_next_idx FROM my_masters WHERE idx >= l_next_idx ORDER BY idx LIMIT 1;

UPDATE current_master SET idx = l_next_idx;

SELECT host, port, log_file, log_pos INTO p_host, p_port, p_file, p_pos FROM my_masters WHERE idx = l_next_idx;END

Select next index, if there is one

Fetch master info using the index

Select the first index, if there were no next index



In pure SQL

CREATE EVENT multi_source ON SCHEDULE EVERY 10 SECOND DOBEGIN DECLARE l_host CHAR(50); DECLARE l_port INT UNSIGNED; DECLARE l_file CHAR(50); DECLARE l_pos BIGINT;

SET SQL_LOG_BIN = 0;

STOP SLAVE; START TRANSACTION; CALL save_current_position(); CALL fetch_next_master(l_host, l_port, l_file, l_pos); CALL change_master(l_host, l_port, 'repl_user', 'xyzzy', l_file, l_pos); COMMIT; START SLAVE;END


Different Tables on Master and Slave

● Upgrading

– Example: Upgrading a topology without downtime● Saving space

– Not keeping big columns on slave● Hiding data

– Keeping data away from users

– Note: still available in binary log and relay log – just not applied to table● Debugging and Auditing

– Adding data for auditing


CREATE TABLE employee ( name CHAR(40), email CHAR(40), changed TIMESTAMP DEFAULT CURRENT_TIMESTAMP ON UPDATE CURRENT_TIMESTAMP)

CREATE TABLE employee ( name CHAR(40), email CHAR(40)

)


● Same initial columns

● Statement-based or row-based replication

More columns on slave

Master Slave


CREATE TABLE employee ( name CHAR(40), email CHAR(40), password CHAR(40))

CREATE TABLE employee ( name CHAR(40), email CHAR(40), password CHAR(40))


● Same initial columns

● Row-based replication only

More columns on master

Master Slave


CREATE TABLE employee ( emp_id TINYINT, name CHAR(40), email CHAR(40))

CREATE TABLE employee ( emp_id INT, name CHAR(40), email CHAR(40))


● Table definitions are identical

… except that some column type are different

Different types of columns on master and slave

Master Slave





● Consider this statement:

INSERT INTO employee VALUES (1, 'Bob', '[email protected]'), (500, 'Alice', '[email protected]')

Slave type conversions

Master Slave

Statement-based

ReplicationWorks fine

Fails silently!








Master Slave

Row-basedReplicationThrows an error!

BeforeMySQL 5.5.3



● @@GLOBAL.SLAVE_TYPE_CONVERSIONS

– Type: SET('ALL_LOSSY', 'ALL_NON_LOSSY')

– Require slave restart

● Non-lossy conversions

– TINYINT INT→

– VARCHAR(32) CHAR(64)→

– FLOAT DOUBLE→

● Lossy conversions

– INT TINYINT→

– CHAR(64) VARCHAR(32)→

– DOUBLE FLOAT →


MySQL 5.5.3and later



● Conversions within same domain possible

– INT, TINYINT, SMALLINT, MEDIUMINT, BIGINT– CHAR(n), VARCHAR(n), TINYTEXT, TEXT, …– DECIMAL(n,m), DOUBLE, FLOAT

● ALL_NON_LOSSY in SLAVE_TYPE_CONVERSIONS

– Conversion to larger domains allowed

● ALL_LOSSY in SLAVE_TYPE_CONVERSIONS

– Conversion to smaller domains allowed (truncation/rounding may occur)




CREATE TABLE employee ( emp_id INT, name VARCHAR(40), email VARCHAR(40))

CREATE TABLE employee ( emp_id TINYINT, name VARCHAR(40), email VARCHAR(40))





Master Slave

Row-basedReplicationWorks fine!

SLAVE_TYPE_CONVERSIONS = 'ALL_NON_LOSSY'



CREATE TABLE employee ( emp_id TINYINT, name VARCHAR(40), email VARCHAR(40))

CREATE TABLE employee ( emp_id INT, name VARCHAR(40), email VARCHAR(40))





Master Slave

Row-basedReplicationThrows an error!

SLAVE_TYPE_CONVERSIONS = 'ALL_NON_LOSSY'



Master and Slave out of sync

● Slave stopped with a strange error

ERROR 1062 (23000): Duplicate entry '3' for key 'PRIMARY'● Compare two databases using mysqldbcompare

mysqldbcompare [email protected] [email protected] employee



$ mysqldbcompare --quiet --server1=root@localhost:3309 --server2=root@localhost:3310 world# Checking databases world on server1 and world on server2#

## Data differences found among rows:--- world.City+++ world.City@@ -1,5 +1,5 @@-+-------+------------+--------------+-----------+-------------+-| ID | Name | CountryCode | District | Population |-+-------+------------+--------------+-----------+-------------+-| 3048 | Stockholm | SWE | Lisboa | 750348 |-+-------+------------+--------------+-----------+-------------+++-------+-----------+--------------+-----------+-------------++| ID | Name | CountryCode | District | Population |++-------+-----------+--------------+-----------+-------------++| 3048 | Helsinki | SWE | Lisboa | 750348 |++-------+-----------+--------------+-----------+-------------+

Comparing two databases and finding the differences



$ mysqldbcompare --quiet --difftype=sql --changes-for=server2 \> [email protected] [email protected] \> world# Checking databases world on server1 and world on server2#

## Transformation for --changes-for=server2:#

# Data differences found among rows:UPDATE world.City SET Name = 'Stockholm' WHERE ID = '3048';

Synchronizing master and slave databases



$ mysqldbcompare --quiet --difftype=sql --changes-for=server1 \> [email protected] [email protected] \> world# Checking databases world on server1 and world on server2#

## Transformation for --changes-for=server1:#

# Data differences found among rows:UPDATE world.City SET Name = 'Helsinki' WHERE ID = '3048';

Synchronizing master and slave databases


Replication Event ChecksumsMaster Slave

EventChecksums


Replication Event Checksums

● Controlling checksum generation (default is CRC32 since 5.6.6)

SET GLOBAL BINLOG_CHECKSUM = CRC32

● Enable verification on events read by dump thread

SET GLOBAL MASTER_VERIFY_CHECKSUM = ON

● Enable verification on events read by SQL thread

SET GLOBAL SLAVE_SQL_VERIFY_CHECKSUM = ON

Configurations and optionsConfigurations and options


The preceding is intended to outline our general product direction. It is intended for information purposes only, and may not be incorporated into any contract. It is not a commitment to deliver any material, code, or functionality, and should not be relied upon in making purchasing decisions. The development, release, and timing of any features or functionality described for Oracle’s products remains at the sole discretion of Oracle.

replication tips & trick for smug

Technology

master master

oracle andor

master log coordinatesrelay

timestamp master

host master

master negotia

change master

binary log positions