Minor wording improvements.

This commit is contained in:
Tom Lane 2006-12-01 03:19:48 +00:00
parent da6daee216
commit f378ccc261

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<!-- $PostgreSQL: pgsql/doc/src/sgml/high-availability.sgml,v 1.14 2006/11/22 18:15:34 momjian Exp $ --> <!-- $PostgreSQL: pgsql/doc/src/sgml/high-availability.sgml,v 1.15 2006/12/01 03:19:48 tgl Exp $ -->
<chapter id="high-availability"> <chapter id="high-availability">
<title>High Availability and Load Balancing</title> <title>High Availability and Load Balancing</title>
@ -12,7 +12,7 @@
<para> <para>
Database servers can work together to allow a second server to Database servers can work together to allow a second server to
quickly take over quickly if the primary server fails (high take over quickly if the primary server fails (high
availability), or to allow several computers to serve the same availability), or to allow several computers to serve the same
data (load balancing). Ideally, database servers could work data (load balancing). Ideally, database servers could work
together seamlessly. Web servers serving static web pages can together seamlessly. Web servers serving static web pages can
@ -50,8 +50,8 @@
committed until all servers have committed the transaction. This committed until all servers have committed the transaction. This
guarantees that a failover will not lose any data and that all guarantees that a failover will not lose any data and that all
load-balanced servers will return consistent results no matter load-balanced servers will return consistent results no matter
which server is queried. Asynchronous updating has a delay between which server is queried. In contrast, asynchronous solutions allow some
the time of commit and its propagation to the other servers, delay between the time of a commit and its propagation to the other servers,
opening the possibility that some transactions might be lost in opening the possibility that some transactions might be lost in
the switch to a backup server, and that load balanced servers the switch to a backup server, and that load balanced servers
might return slightly stale results. Asynchronous communication might return slightly stale results. Asynchronous communication
@ -101,7 +101,7 @@
standby server should never access the shared storage while standby server should never access the shared storage while
the primary server is running. It is also possible to use the primary server is running. It is also possible to use
some type of file system mirroring to keep the standby server some type of file system mirroring to keep the standby server
current, but the mirroring must be done in a way that the current, but the mirroring must be done in a way that ensures the
standby server has a consistent copy of the file system. standby server has a consistent copy of the file system.
</para> </para>
@ -159,10 +159,10 @@ protocol to make nodes agree on a serializable transactional order.
<para> <para>
With statement-based replication middleware, a program intercepts With statement-based replication middleware, a program intercepts
every SQL query and sends it to all servers. Each server every SQL query and sends it to one or all servers. Each server
operates independently. Read-only queries can be sent to a operates independently. Read-write queries are sent to all servers,
single server because there is no need for all servers to while read-only queries can be sent to just one server, allowing
process it. the read workload to be distributed.
</para> </para>
<para> <para>