High Availability with MariaDB Enterprise

© SkySQL Corpora-on Ab. Company Confiden-al. 09/06/2014

© SkySQL Corpora-on Ab. Company Confiden-al.

High Availability with MariaDB Enterprise

Stephane Varoqui Professional Services, SkySQL

* * 09/06/2014


Agenda

❏  Introduc-on to High Availability ❏ Different services that need HA ❏ Different components of High Availability ❏ Different MariaDB HA Solu-ons

❏  HA using MariaDB Replica-on ❏  HA using MariaDB Galera Cluster

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Introduc-on to High Availability

High availability is a system design protocol and associated

implementation that ensures a certain degree of operational continuity during

a given measurement period

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❏ High Availability != Long Up*me “up” might s-ll not be accessible “down” just once, but for a long *me

❏ High Availability rather means Long Mean Time Between Failures (MTBF) Short Mean Time To Recover (MTTR)



❏  Availability level is measured as the ra-o of -me the system is available over a year, expressed as a percentage

❏  99.9% availability means that the system is available at least 8751 of 8760 hours in a year, or that it is unavailable at the most 9 hours per year

❏  99.999% availability means that the system is available at least 525595 or 525600 minutes in a year, or that it is unavailable at the most 5 minutes per year

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Maintaining High Availability

❏  There are two common situa-ons that we try to protect ourselves from using an HA solu-on

❏  Datacenter failure – A whole datacenter becomes unavailable for some reason, like power failure, network failure, a virus or similar situa-ons

❏  Server failure – An individual server fails because of a hardware failure or something similar

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Layers in HA Solu-on

❏  All services that make up the applica-on stack needs HA for the system to achieve HA

Web servers Applica-on servers Applica-ons Database servers Storage Network

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TCO for Unbreakable

Hardware


Services in an HA Solu-on

❏ Of the different types of services, there are two types Stateless services

These servers has no state beyond the current opera-on. If such a server fails, another server of the same type can replace it without having to transfer any set of data. Webservers and applica-on servers are typical stateless services

Stateful services These services maintains a state, and that state needs to be preserved if a server fails, and has to be made available to any other server that takes it place. A database service such as a MariaDB server is a typical stateful service

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Components of High Availability

❏ Monitoring and Management Availability of the services needs to be monitored, to be able to take ac-on when there is a failure. A failover can be manual or automa-c, but it has to be managed

❏  Failover / Load Balancing mechanism Some mechanism to redirect traffic from the failed server or Datacenter and to a working one

❏ Data redundancy For stateful services, we need to make sure that data is somehow made redundant

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Monitoring and Management

❏  There are many different solu-ons here, some focused on specific services (in par-cular database), some as part of a Load Balancing sodware solu-on of an Appliance or a pure sodware based solu-on such as LinuxHA, HaProxy, MaxScale, Mha

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Failover mechanism

❏  There is a wide range of op-ons here too, in par-cular when it comes to Datacenter failover, which can be more complicated

❏  Common mechanisms range from applica-on based failover and DNS failover to Load Balancing and Network Failover

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Data Redundancy

❏  Providing Data Redundancy is complex, error prone and takes a toll on performance

❏  It also has to be men-oned that a SAN does not provide redundancy just because a disk set can be failed over from one server to another. A SAN might be a SPOF, but in some cases that is a risk that some customers is willing to take

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Data Redundancy with MariaDB

❏ MariaDB Internal Replica*on ❏  Assync ❏  Semi-‐sync ❏  Sync per table with spider

❏ MariaDB Galera Cluster

❏  Storage based redundancy (Ac-ve / Passive setups) ❏  DRBD (Distributed Replicated Block Device) ❏  SAN (Storage Area Network) ❏  VMWare replica-on

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HA using MariaDB Replica-on

❏  In many cases best solu-on

❏  Well known and easy to use technology

❏  The cluster is very loosely coupled, not all nodes are aware of all the other nodes for example it’s self healing solu-on, no sensibility to network latency, and replica-on node speed (hardware variability)

❏  Offer the lowest master performance impact so far

❏  Mul* node read scalability with best possible query latency, network data distribu-on s-ll slow vs in memory scale up (photonic bus & memory is for 2020)

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❏  In many cases the best solu-on

❏  Logical replica-on no corrup*on propagated

❏  Various topologies using mul- source , storage engine switching, mul- master , peer to peer

❏  Row vs Statement for strong network compression

❏ MariaDB fixing the gotcha

❏  Parallel replica-on , group commit, checksum, heartbeat

❏  Can be extended with per session consistency using GTID_POS_WAIT

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HA MariaDB Replica-on GTID

SET GLOBAL GTID_SLAVE_POS = BINLOG_GTID_POS("master-bin.00024", 1600);

CHANGE MASTER TO master_host="10.2.3.4", master_use_gtid=slave_pos; START SLAVE;

CHANGE MASTER TO master_host="10.2.3.5";



❏ Replica-on gotcha

❏  Can lose data on master crash without semi-‐sync and semi sync performance should be address in next release

❏  Adding a slave stay manual and complex (MyISAM)

❏  Failover is more complex, found the most up to date slave, depends external product like MHA and scrip-ng to LB or HA solu-ons (maxscale can fix)

❏  Automa-c Strong consistency (maxscale can fix)

❏  No map reduce queries (spider temporary table can fix)

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HA using MariaDB ❏  This a sodware-‐only solu-on

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MariaDB Server MariaDB Server MariaDB Server

Galera wsrep Library Galera wsrep Library Galera wsrep Library

Synchronous Replication

Load Balancer / Failover

Application / Application server


Installing MariaDB

❏  MariaDB Galera Cluster consists of separate MariaDB binary that in turns talks to the Galera wsrep library

❏  Once set up, Galera is configured using the usual my.cnf file, and is monitored using the SHOW GLOBAL STATUS command

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HA using MariaDB

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❏  Scales reads

❏  Limited impact on concurrent writes, despite long distance network latency

❏  Proper Cluster with easy failover, op-mis-c locking, split-‐brain protec-on, no possible data lost on failover

❏  Synchronous replica*on with low overhead due to op-mis-c locking , paxos queue, parallel event replica-on

❏  Transparent provisioning

❏ Galera best point


HA using MariaDB

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❏  InnoDB only solu-on

❏  Network architecture reliability

❏  Local CommiUed Read only (select for update)

❏  Deadlock error prone

❏ Galera dark side

For transac-onal scenarios it may s-ll need read write spliVng !


Failover with MariaDB

❏  MariaDB Galera Cluster handles failed servers internally provide a status, that tells about membership of the cluster

❏  MariaDB Galera Cluster also handles split-‐brain protec*on and this requires at least 3 servers

❏  MariaDB Galera Cluster can also be configured without split-‐brain protec*on, for example when failover is manual or is handled in some other way

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Sejng up MariaDB

❏  Necessary to allow for protec-on against split-‐brain scenarios, but only using 2 database servers, a third server can be set up with a Galera specific arbitra-on agent (grbd)

❏  Galera also can be used with it’s own simple Load Balancer, (glb) , auto detect new nodes, although it is much more common that other technologies are used, such as HA aware Connectors or a Load Balancer, in this case use a backup policy and no load balancing for write

❏  For advance setup without applica*on control, auto balancing reads and write to a single node we advise you to try out our maxscale proxy

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Ques*ons?

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Software

High Availability with MariaDB Enterprise