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Clarify replication items, and define some terms.

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Bruce Momjian 2006-11-16 18:25:58 +00:00
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commit c7a6046a59
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doc/src/sgml/failover.sgml
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<!-- $PostgreSQL: pgsql/doc/src/sgml/failover.sgml,v 1.6 2006/11/15 01:09:08 momjian Exp $ -->
<!-- $PostgreSQL: pgsql/doc/src/sgml/failover.sgml,v 1.7 2006/11/16 18:25:58 momjian Exp $ -->
<chapter id="failover">
<title>Failover, Replication, Load Balancing, and Clustering Options</title>
@ -32,6 +32,18 @@
minimizes its impact for a specific workload.
</para>
<para>
Some solutions deal with synchronization by allowing only one
server to modify the data. Servers that can modify data are
called read/write or "master" server. Servers with read-only
data are called backup or "slave" servers. As you will see below,
these terms cover a variety of implementations. Some servers
are masters of some data sets, and slave of others. Some slaves
cannot be accessed until they are changed to master servers,
while other slaves can reply to read-only queries while they are
slaves.
</para>
<para>
Some failover and load balancing solutions are synchronous, meaning that
a data-modifying transaction is not considered committed until all
@ -118,15 +130,20 @@
<title>Data Partitioning</title>
<para>
Data partitioning splits tables into data sets. Each set can only be
modified by one server. For example, data can be partitioned by
offices, e.g. London and Paris. While London and Paris servers have all
data records, only London can modify London records, and Paris can only
modify Paris records.
Data partitioning splits tables into data sets. Each set can
be modified by only one server. For example, data can be
partitioned by offices, e.g. London and Paris. While London
and Paris servers have all data records, only London can modify
London records, and Paris can only modify Paris records. This
is similar to section <xref
linkend="continuously-running-replication-server"> above, except
that instead of having a read/write server and a read-only server,
each server has a read/write data set and a read-only data
set.
</para>
<para>
Such partitioning implements both failover and load balancing. Failover
Such partitioning provides both failover and load balancing. Failover
is achieved because the data resides on both servers, and this is an
ideal way to enable failover if the servers share a slow communication
channel. Load balancing is possible because read requests can go to any