High Availability with MariaDB Enterprise by Stéphane Varoqui. Presented 26.6.2014 at the MariaDB Roadshow in Paris, France.

1. © SkySQL Corporation Ab. Company Confidential.09/06/2014

2. © SkySQL Corporation Ab. Company Confidential.
High Availability with MariaDB Enterprise
Stephane Varoqui
Professional Services, SkySQL
* *09/06/2014

3. © SkySQL Corporation Ab. Company Confidential.
Agenda
❏ Introduction to High Availability
❏ Different services that need HA
❏ Different components of High Availability
❏ Different MariaDB HA Solutions
❏ HA using MariaDB Replication
❏ HA using MariaDB Galera Cluster
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Introduction 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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Introduction to High Availability
09/06/2014
❏ High Availability != Long Uptime
“up” might still not be accessible
“down” just once, but for a long time
❏ High Availability rather means
Long Mean Time Between Failures (MTBF)
Short Mean Time To Recover (MTTR)

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Introduction to High Availability
❏ Availability level is measured as the ratio of time
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 situations that we try to
protect ourselves from using an HA solution
❏ Datacenter failure – A whole datacenter
becomes unavailable for some reason, like
power failure, network failure, a virus or similar
situations
❏ Server failure – An individual
server fails because of a
hardware failure or something
similar
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Layers in HA Solution
❏ All services that make up the application stack
needs HA for the system to achieve HA
Web servers
Application servers
Applications
Database servers
Storage
Network
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TCO for
Unbreakable
Hardware

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Services in an HA Solution
❏ Of the different types of services, there are
two types
Stateless services
These servers has no state beyond the current operation. If such a
server fails, another server of the same type can replace it without
having to transfer any set of data. Webservers and application
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 action when there is a failure.
A failover can be manual or automatic, 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 solutions here, some
focused on specific services (in particular
database), some as part of a Load Balancing
software solution of an Appliance or a pure
software based solution such as LinuxHA,
HaProxy, MaxScale, Mha
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Failover mechanism
❏ There is a wide range of options here too, in
particular when it comes to Datacenter
failover, which can be more complicated
❏ Common mechanisms range from application
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 mentioned 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 Replication
❏ Assync
❏ Semi-sync
❏ Sync per table with spider
❏ MariaDB Galera Cluster
❏ Storage based redundancy (Active / Passive setups)
❏ DRBD (Distributed Replicated Block Device)
❏ SAN (Storage Area Network)
❏ VMWare replication
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HA using MariaDB Replication
❏ In many cases best solution
❏ 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
solution, no sensibility to network latency, and
replication node speed (hardware variability)
❏ Offer the lowest master performance impact so far
❏ Multi node read scalability with best possible query
latency, network data distribution still slow vs in memory
scale up (photonic bus & memory is for 2020)
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HA using MariaDB Replication
❏ In many cases the best solution
❏ Logical replication no corruption propagated
❏ Various topologies using multi source , storage engine
switching, multi master , peer to peer
❏ Row vs Statement for strong network compression
❏ MariaDB fixing the gotcha
❏ Parallel replication , group commit, checksum, heartbeat
❏ Can be extended with per session consistency using
GTID_POS_WAIT
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HA MariaDB Replication 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";

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HA using MariaDB Replication
❏ Replication 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 scripting
to LB or HA solutions (maxscale can fix)
❏ Automatic Strong consistency (maxscale can fix)
❏ No map reduce queries (spider temporary table can fix)
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HA using MariaDB
❏ This a software-only solution
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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

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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, optimistic locking, split-
brain protection, no possible data lost on failover
❏ Synchronous replication with low overhead due to
optimistic locking , paxos queue, parallel event replication
❏ Transparent provisioning
❏ Galera best point

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HA using MariaDB
09/06/2014
❏ InnoDB only solution
❏ Network architecture reliability
❏ Local Committed Read only (select for update)
❏ Deadlock error prone
❏ Galera dark side
For transactional scenarios it may still
need read write splitting !

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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 protection
and this requires at least 3 servers
❏ MariaDB Galera Cluster can also be configured without
split-brain protection, for example when failover is manual
or is handled in some other way
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Setting up MariaDB
❏ Necessary to allow for protection against split-brain
scenarios, but only using 2 database servers, a third server
can be set up with a Galera specific arbitration 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 application control, auto
balancing reads and write to a single node we advise you to
try out our maxscale proxy
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Questions?
09/06/2014