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ca21417a
编写于
11月 14, 2006
作者:
B
Bruce Momjian
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Update failover docs, per suggestions from Chris Browne.
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doc/src/sgml/failover.sgml
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<!-- $PostgreSQL: pgsql/doc/src/sgml/failover.sgml,v 1.
3 2006/10/27 12:40:26
momjian Exp $ -->
<!-- $PostgreSQL: pgsql/doc/src/sgml/failover.sgml,v 1.
4 2006/11/14 21:43:00
momjian Exp $ -->
<chapter id="failover">
<chapter id="failover">
<title>Failover, Replication, Load Balancing, and Clustering Options</title>
<title>Failover, Replication, Load Balancing, and Clustering Options</title>
...
@@ -108,7 +108,7 @@
...
@@ -108,7 +108,7 @@
</para>
</para>
<para>
<para>
Slony is an example of this type of replication, with per-table
Slony
-I
is an example of this type of replication, with per-table
granularity. It updates the backup server in batches, so the replication
granularity. It updates the backup server in batches, so the replication
is asynchronous and might lose data during a fail over.
is asynchronous and might lose data during a fail over.
</para>
</para>
...
@@ -138,8 +138,8 @@
...
@@ -138,8 +138,8 @@
<para>
<para>
Data partitioning is usually handled by application code, though rules
Data partitioning is usually handled by application code, though rules
and triggers can be used to keep the read-only data sets current. Slony
and triggers can be used to keep the read-only data sets current. Slony
-I
can also be used in such a setup. While Slony replicates only entire
can also be used in such a setup. While Slony
-I
replicates only entire
tables, London and Paris can be placed in separate tables, and
tables, London and Paris can be placed in separate tables, and
inheritance can be used to access both tables using a single table name.
inheritance can be used to access both tables using a single table name.
</para>
</para>
...
@@ -158,11 +158,13 @@
...
@@ -158,11 +158,13 @@
</para>
</para>
<para>
<para>
This can be complex to set up because functions like random()
Because each server operates independently, functions like
and CURRENT_TIMESTAMP will have different values on different
<function>random()</>, <function>CURRENT_TIMESTAMP</>, and
servers, and sequences should be consistent across servers.
sequences can have different values on different servers. If
Care must also be taken that all transactions either commit or
this is unacceptable, applications must query such values from
abort on all servers Pgpool is an example of this type of
a single server and then use those values in write queries.
Also, care must also be taken that all transactions either commit
or abort on all servers Pgpool is an example of this type of
replication.
replication.
</para>
</para>
</sect1>
</sect1>
...
@@ -173,13 +175,23 @@
...
@@ -173,13 +175,23 @@
<para>
<para>
In clustering, each server can accept write requests, and these
In clustering, each server can accept write requests, and these
write requests are broadcast from the original server to all
write requests are broadcast from the original server to all
other servers before each transaction commits. Under heavy
other servers before each transaction commits. Heavy write
load, this can cause excessive locking and performance degradation.
activity can cause excessive locking, leading to poor performance.
It is implemented by <productname>Oracle</> in their
In fact, write performance is often worse than that of a single
server. Read requests can be sent to any server. Clustering
is best for mostly read workloads, though its big advantage is
that any server can accept write requests --- there is no need
to partition workloads between read/write and read-only servers.
</para>
<para>
Clustering is implemented by <productname>Oracle</> in their
<productname><acronym>RAC</></> product. <productname>PostgreSQL</>
<productname><acronym>RAC</></> product. <productname>PostgreSQL</>
does not offer this type of load balancing, though
does not offer this type of load balancing, though
<productname>PostgreSQL</> two-phase commit can be used to
<productname>PostgreSQL</> two-phase commit (<xref
implement this in application code or middleware.
linkend="sql-prepare-transaction-title"> and <xref linkend=
"sql-commit-prepared-title">) can be used to implement this in
application code or middleware.
</para>
</para>
</sect1>
</sect1>
...
@@ -187,12 +199,12 @@
...
@@ -187,12 +199,12 @@
<title>Clustering For Parallel Query Execution</title>
<title>Clustering For Parallel Query Execution</title>
<para>
<para>
This allows multiple servers to work
on a single query. On
e
This allows multiple servers to work
concurrently on a singl
e
possible way this could work is for the data to be split among
query. One possible way this could work is for the data to be
s
ervers and for each server to execute its part of the query
s
plit among servers and for each server to execute its part of
and results sent to a central server to be combined and retur
ned
the query and results sent to a central server to be combi
ned
to the user. There currently is no <productname>PostgreSQL</>
and returned to the user. There currently is no
open source solution for this.
<productname>PostgreSQL</>
open source solution for this.
</para>
</para>
</sect1>
</sect1>
...
...
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