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Data is the currency of today's web, mobile, social, enterprise and cloud applications. Ensuring data is always available is a top priority for any organization. Minutes of downtime can result in significant loss of revenue and reputation.
There is no “one size fits all” approach to delivering High Availability (HA). Unique application attributes, business requirements, operational capabilities and legacy infrastructure can all influence HA technology selection. And technology is only one element in delivering HA: people and processes are just as critical as the technology itself.
MySQL is deployed into many applications demanding availability and scalability. Availability refers to the ability to cope with, and if necessary recover from, failures on the host, including failures of MySQL, the operating system, or the hardware and maintenance activity that may otherwise cause downtime. Scalability refers to the ability to spread both the database and the load of your application queries across multiple MySQL servers.
Because each application has different operational and availability requirements, MySQL offers a range of certified and supported solutions, delivering the appropriate levels of High Availability (HA) and scalability to meet service level requirements. Such solutions extend from replication, through virtualization and geographically redundant, multi-data center solutions delivering 99.999% uptime.
Selecting the right high availability solution for an application largely depends on:
The level of availability required.
The type of application being deployed.
Accepted best practices within your own environment.
The primary solutions supported by MySQL include:
MySQL Replication. Learn more: Chapter 17, Replication
MySQL Cluster. Learn more: MySQL Cluster NDB 7.3 and MySQL Cluster NDB 7.4
Oracle VM Template for MySQL. Learn more: Section 16.1, “Oracle VM Template for MySQL Enterprise Edition”.
MySQL with DRBD with Corosync and Pacemaker. Learn more: Section 16.2, “Overview of MySQL with DRBD/Pacemaker/Corosync/Oracle Linux”.
MySQL with Windows Failover Clustering. Learn more: Section 16.3, “Overview of MySQL with Windows Failover Clustering”.
MySQL with Solaris Cluster. Learn more about Solaris Cluster.
Further options are available using third-party solutions.
Each architecture used to achieve highly available database services is differentiated by the levels of uptime it offers. These architectures can be grouped into three main categories:
Clustered & Virtualized Systems.
Shared-Nothing, Geographically-Replicated Clusters.
As illustrated in the following figure, each of these architectures offers progressively higher levels of uptime, which must be balanced against potentially greater levels of cost and complexity that each can incur. Simply deploying a high availability architecture is not a guarantee of actually delivering HA. In fact, a poorly implemented and maintained shared-nothing cluster could easily deliver lower levels of availability than a simple data replication solution.
The following table compares the HA and Scalability capabilities of the various MySQL solutions:
Table 16.1 Feature Comparison of MySQL HA Solutions
|Requirement||MySQL Replication||DRBD||Oracle VM Template||MySQL Cluster|
|Platform Support||All Supported by MySQL Server (http://www.mysql.com/support/supportedplatforms/database.html)||Linux||Oracle Linux||All Supported by MySQL Cluster (http://www.mysql.com/support/supportedplatforms/cluster.html)|
|Automated IP Failover||No||Yes||Yes||Depends on Connector and Configuration|
|Automated Database Failover||No||Yes||Yes||Yes|
|Automatic Data Resynchronization||No||Yes||N/A - Shared Storage||Yes|
|Typical Failover Time||User / Script Dependent||Configuration Dependent, 60 seconds and Above||Configuration Dependent, 60 seconds and Above||1 Second and Less|
|Synchronous Replication||No, Asynchronous and Semisynchronous||Yes||N/A - Shared Storage||Yes|
|Shared Storage||No, Distributed||No, Distributed||Yes||No, Distributed|
|Geographic redundancy support||Yes||Yes, via MySQL Replication||Yes, via MySQL Replication||Yes, via MySQL Replication|
|Update Schema On-Line||No||No||No||Yes|
|Number of Nodes||One Master, Multiple Slaves||One Active (primary), one Passive (secondary) Node||One Active (primary), one Passive (secondary) Node||255|
|Built-in Load Balancing||Reads, via MySQL Replication||Reads, via MySQL Replication||Reads, via MySQL Replication & During Failover||Yes, Reads and Writes|
|Supports Read-Intensive Workloads||Yes||Yes||Yes||Yes|
|Supports Write-Intensive Workloads||Yes, via Application-Level Sharding||Yes, via Application-Level Sharding to Multiple Active/Passive Pairs||Yes, via Application-Level Sharding to Multiple Active/Passive Pairs||Yes, via Auto-Sharding|
|Scale On-Line (add nodes, repartition, etc.)||No||No||No||Yes|