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<chapter id="high-availability">

<title>High Availability and Load Balancing</title>

other server before each transaction commits. Heavy write

activity can cause excessive locking, leading to poor performance.

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 &mdash; there is

no need to partition workloads between master and slave servers,

and because the data changes are sent from one server to another,

server. Read requests can be sent to any server. Some

implementations use cluster-wide shared memory or shared disk

to reduce the communication overhead. Clustering is best for

mostly read workloads, though its big advantage is that any

server can accept write requests &mdash; there is no need to

partition workloads between master and slave servers, and

because the data changes are sent from one server to another,

there is no problem with non-deterministic functions like

<function>random()</>.

</para>