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