Database Reference
In-Depth Information
See also
Clusterware may provide additional features, such as automated failover, monitoring, or ease
of management of replication.
Repmgr is an open source tool designed specifically for PostgreSQL replication. To get
additional information about repmgr visit the following URL:
http://projects.2ndQuadrant.com/repmgr/
Continuent Tungsten is a commercial clusterware product that also supports PostgreSQL,
and is available at the following URL:
http://www.continuent.com/
Managing Hot Standby
Hot Standby is the name for the PostgreSQL feature that allows us to connect to a Standby
database and execute read-only queries. Most importantly, Hot Standby allows us to run
queries while the Standby is being continuously updated through either file-based or
streaming replication.
Hot Standby allows you to offload larger queries or parts of your read-only workload onto
the Standby nodes. Should you need to failover to the Standby node, your queries will keep
executing during the failover process to avoid any interruption of service.
There are some complexities that need to be understood to manage Hot Standby successfully,
as in some cases user queries can conflict with the continuous application of changes from
the Master. If no new changes arrive, no conflicts will arise.
There are two main roles we need to consider with hot Standby. First, that the Standby node
provides a secondary node in case the primary node fails. Second, that we can run queries on
that node. In some cases, those two roles can come into conflict with each other, and we need
to decide ahead of time the importance we attach to each role.
In most cases, the role of Standby will take priority: queries are good, but its OK to cancel
them to ensure we have a viable Standby. If we have more than one hot Standby node, it may
be possible to have one node nominated as Standby and others dedicated to serving queries,
without regard for their need to act as Standbys.
Getting ready
Hot Standby is usable with the following:
F
File-based replication
F
Streaming replication
