three things are certain in life: taxes, death, and …multi-master (master-master) technologicky...
TRANSCRIPT
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Replikace databází
�Three things are certain in life: Taxes, death, and data loss.
Guess which has just occurred.�
-- Operating system error message
Ond ej e ák, VUT FEL, Y36DBA� � � �
�
-- Jan Wiecky, Slony-I
Ond ej e ák, VUT FEL, Y36DBA� � � �
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Replikace databází, Obsah
� p edstavení �� motivace� �nep ímé� replikace�� replikace v MySQL a v PostgreSQL � v celém p ísp vku tisíc a jeden buzzword :)� �� replikace v PostgreSQL pomocí Slony-I
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Replikace
� Replication (in computer science) is the process of sharing information so as to ensure the consistency between redundant resources, such as software or hardware components, to improve reliability, fault-tolerance or accessibility. http://en.wikipedia.org/wiki/Replication_(computer_science)
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Motivace
�The value of data stored on a computer, often far exceeds the value of the computer! Hardware can be quickly and easily replaced, but data cannot! Companies often insure there computer hardware against theft and loss, but fail to backup their data, which is far more precious!�
-- T.E. Ronneberg
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Motivace, mo�né scéná e�
� �stand-by backup�/�hot-spare backup�� �zero-downtime upgrades�� development servers� load balancing
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Ú el�
� pozor, replikace není zálohování, ale spí�e disaster-recovery� zálohy (u�ivatel si sma�e soubor)� archivace (u�ivatel chce rok starou verzi dat)� vysoká dostupnost (HA, high-availability)
� m �e souviset s rozkládáním zát �e (load � �balancing)
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Replikace nep ímo�
� tém r v�dy m �eme replikovat na úrovni � �opera ního systému nebo databázového �systému� tedy replikace databáze nep ímo�
� replikace souborového systému� sdílený prostor s daty
� pravidelnou zálohou a obnovou databáze
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Replikace databází
� hlavní koncepty:� podle typu replikace
� master/slave� v�dy pouze jeden master, který provádí zm ny, které se dál �
�í í na slaves�� heartbeat failover� riziko �split-brain situation�, kdy si n kolik systém myslí, �e � �
jsou master � e�ením je pak typicky fencing a STONITH �(Shoot The Other Node In The Head)
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Replikace databází
� hlavní koncepty:� podle typu replikace
� master/slave� multi-master (master-master)
� technologicky více sexy, zm nu m �e ud lat ka�dý node� � �� náro n j�í implementace a provoz (typicky aktivní ochrana � �
p ed konflikty transakcí)�
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Replikace databází
� hlavní koncepty:� podle typu replikace
� master/slave� multi-master
� podle zp sobu ulo�ení dat�� asynchronní
� zm na je potvrzena, jakmile se provede lokáln� �� vysoký výkon za cenu mo�né ztráty dat
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Replikace databází
� hlavní koncepty:� podle zp sobu ulo�ení dat�
� asynchronní� synchronní
� garantuje nulovou ztrátu dat� nep ekonatelná zpo�d ní � nap íklad rychlost sv tla (cca � � � �
67 s na 10 km, u lokálního potvrzení zápis bloku za cca �10-20 s) �
� systém zamrzne u� p i ztrát jednoho node a nebo spojení, � �z definice (!)
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Replikace MySQL
� out-of-the-box, podpora od verze 3.23� asynchronní� mnoho replika ních scéná� ��
� single master, single slave� single master, multiple slaves� kaskádová replikace od jednoho mastera� master-master
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Replikace MySQL
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Replikace MySQL
� do verze 5.1 byla replikace zalo�ená na p enosu SQL dotaz� �
� v sou asné dob se p ená�í binární log row-� � �based (konfigurovatelné, r zné chování �vzhledem k aplikaci) zm n v celém systému, �datábázi a nebo tabulkách
� single-threaded (bottleneck!)
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Nastavení replikace MySQL
� master-slave replikace� MySQL masteru musí být sí ov dostupná� �� GRANT REPLICATION SLAVE ON *...� binlogdo_db = replicated� mysqldump & restore
� server-id = 2� CHANGE MASTER, START SLAVE
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Co nás eká v MySQL 5.5�
� MySQL 5.5 je momentáln pre-release�� umo� uje semi-synchronní replikace�
� data z masteru jsou p enesena na slave, kde �jsou pouze zapsána do logu
� jakmile master ví, �e data jsou v logu slave, provede commit
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Dal�í mo�nosti replikování MySQL
� MySQL Proxy
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Dal�í mo�nosti replikování MySQL
� MySQL Proxy� MySQL NDB Cluster
� shared-nothing architecture� in-memory� synchronní replikace (dvoj-fázový commit)� no SPOF (Single Point of Failure) � n které funkce chybí (nap . cizí klí e)� � �
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Dal�í mo�nosti replikování MySQL
� MySQL Proxy� MySQL NDB Cluster� Continuent Tungsten middleware
� aplika ní server nad MySQL�� synchronní replikace
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Dal�í mo�nosti replikování MySQL
� MySQL Proxy� MySQL NDB Cluster� Continuent Tungsten middleware� Federated storage engine
� tabulky na vzdálených strojích
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Dal�í mo�nosti replikování MySQL
� MySQL Proxy� MySQL NDB Cluster� Continuent Tungsten middleware� Federated storage engine� HiveDB
� partitioning
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Replikace PostgreSQL
� WAL (Write-Ahead Log) od verze 7.1� asynchronní� plná podpora a� od verze 9.0� skromné replika ní scéná e� �
� single master, single slave� single master, multiple slaves� ... a nic víc :)
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Replikace PostgreSQL
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Replikace PostgreSQL
� úpravy z masteru jsou zapisovány p ímo �do WAL na slave
� slave promítá zm ny a to p ímo raw data, ne � �jednotlivé dotazy kv li rychlosti, tzn. je �bezpe n j�í pro � � INSERTy s NOW(), function() apod.)
� také single-threaded
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Nastavení replikace PostgreSQL
� master-slave replikace� PostgreSQL na masteru musí být sí ov � �
dostupný� wal_level = hot_standby� archive_mode = on� pg_dump & restore
� hot_standby = on� standby_mode = on, primary_conninfo
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Co nás eká v nové verzi�
� synchronní replikace v 9.1� �no formal requirements for each
PostgreSQL release� :)� Postgres-R
� multi-master
� Postgres-XC� synchronní multi-master shared-nothing
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Dal�í mo�nosti replikování PgSQL
� Slony-I� trigger-based replikace� master-slave, s �ir�í podporou replika ních �
scéná��
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Dal�í mo�nosti replikování PgSQL
� Slony-I� Londiste
� replika ní systém nad PostgreSQL�� sou ástí SkyTools od Skype�
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Dal�í mo�nosti replikování PgSQL
� Slony-I� Londiste� Bucardo
� také multi-master replikace� aplika ní server v Perlu�
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Dal�í mo�nosti replikování PgSQL
� Slony-I� Londiste� Bucardo� pgpool-II
� aplika ní proxy�
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Dal�í mo�nosti replikování PgSQL
� Slony-I� Londiste� Bucardo� pgpool-II� Continuent Tungsten middleware
� jako u MySQL
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Dal�í mo�nosti replikování PgSQL
� Slony-I� Londiste� Bucardo� pgpool-II� Continuent Tungsten� EnterpriseDB
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Srovnání MySQL a PostgreSQL
� MySQL� statement-based
� men�í logy, ale pozor na UDF, DML apod.
� row-based
� PostgreSQL� latter-based
� nejbezpe n j�í� �
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Srovnání MySQL a PostgreSQL
� MySQL� mnoho replika ních scéná� ��
� v etn �ring replication�� �
� PostgreSQL� pouze pár replika ních scéná� ��
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Srovnání MySQL a PostgreSQL
� MySQL� umo� uje filtrování replikovaných dat (nap íklad � �
replikace konkrétní tabulky)
� PostgreSQL� filtrování není podporováno
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Srovnání MySQL a PostgreSQL
� MySQL� single-threaded replication
� PostgreSQL� single-threaded replication
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Srovnání MySQL a PostgreSQL
� MySQL� SHOW p íkazy pro správu a monitoring�
� PostgreSQL� mo�nost sledovat datový rozdíl (vzdálenost)
mezi master a slave
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Srovnání MySQL a PostgreSQL
� oba systémy jsou dobrou volbou na replikování
� ka�dý má svá pro a proti
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Replikace pomocí Slony-I
� Slony-I umo� uje asynchronní, master-slave �replikaci zalo�enou na TRIGGERech v databázi s daty
� sleduje zm ny v datech a následn je � �provádí v celém replika ním clusteru�
� jeho konfigurace je pom rn slo�itá� �
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Principy replikace pomocí Slony-I
� master node s n kolika slaves�� AFTER ROW triggery na unikátních ádcích�
� replika ní daemoni (Slon)�� replikace events� konfigura ní jazyk Slonik�
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P íklad�
� jednoduchá replikace mezi dv ma nody�� instalace PostgreSQL, Slony� konfigurace PostgreSQL pro sí ovou �
komunikaci� vytvo ení u�ivatel pro Slony� �� podpora PL/pgSQL� konfigurace pro Slonik
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Konfigurace pro Slonik #!/bin/sh slonik << EOF
cluster name = first;
node 1 admin conninfo = 'dbname=pgbench host=192.168.1.1 ...';
node 2 admin conninfo = 'dbname=pgbenchslave host=192.168.1.2 ...'
init cluster (id=1, comment = 'Master Node');
...
create set (id=1, origin=1, comment='All pgbench tables');
set add table (set id=1, origin=1, id=1,
fully qualified name = 'public.accounts', comment='accounts table');
...
EOF
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Konfigurace pro Sloník � SQL
� Slonik p ekládá do SQL, které se dá volat �také p ímo:�
-- Initialize local node
SELECT @[email protected](@MASTER_NODE_ID@, '@MASTER_NODE_NAME@');
SELECT @[email protected](@MASTER_NODE_ID@);
-- Create replication set
SELECT @[email protected](@REPSET_ID@, '@REPSET_NAME@');
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Konfigurace pro Slonik #!/bin/sh slonik << EOF
cluster name = first;
node 1 admin conninfo = 'dbname=pgbench host=192.168.1.1 ...';
node 2 admin conninfo = 'dbname=pgbenchslave host=192.168.1.2 ...'
init cluster (id=1, comment = 'Master Node');
...
create set (id=1, origin=1, comment='All pgbench tables');
set add table (set id=1, origin=1, id=1,
fully qualified name = 'public.accounts', comment='accounts table');
...
EOF
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... d kuji za pozornost �
Pou�ité zdroje:� Wikipedia [http://www.slony.info/]� Slony-I Homepage [http://www.slony.info/] � http://www.theserverside.com/feature/Compa
ring-MySQL-and-Postgres-90-Replication � MySQL.com, PostgreSQL.com