<para>

Several <application>libpq</application> functions parse a user-specified string to obtain

connection parameters. There are two accepted formats for these strings:

plain<literal>keyword = value</literal> strings

plain keyword/value strings

and URIs. URIs generally follow

<ulink url="https://tools.ietf.org/html/rfc3986">RFC

3986</ulink>, except that multi-host connection strings are allowed

<title>Keyword/Value Connection Strings</title>

<para>

In the first format, each parameter setting is in the form

<literal>keyword = value</literal>. Spaces around the equal sign are

In the keyword/value format, each parameter setting is in the form

<replaceable>keyword</replaceable> <literal>=</literal>

<replaceable>value</replaceable>, with space(s) between settings.

Spaces around a setting's equal sign are

optional. To write an empty value, or a value containing spaces, surround it

with single quotes,e.g.,<literal>keyword = 'a value'</literal>. Single

quotes and backslashes within

the value must be escaped with a backslash, i.e., <literal>\'</literal> and

with single quotes,for example<literal>keyword = 'a value'</literal>.

Singlequotes and backslashes within

a value must be escaped with a backslash, i.e., <literal>\'</literal> and

<literal>\\</literal>.

</para>

<para>

The general form for a connection <acronym>URI</acronym> is:

<synopsis>

postgresql://[user[:password]@][host][:port][,...][/dbname][?param1=value1&amp;...]

postgresql://<optional><replaceable>userspec</replaceable>@</optional><optional><replaceable>hostspec</replaceable></optional><optional>/<replaceable>dbname</replaceable></optional><optional>?<replaceable>paramspec</replaceable></optional>

<phrase>where <replaceable>userspec</replaceable> is:</phrase>

<replaceable>user</replaceable><optional>:<replaceable>password</replaceable></optional>

<phrase>and <replaceable>hostspec</replaceable> is:</phrase>

<optional><replaceable>host</replaceable></optional><optional>:<replaceable>port</replaceable></optional><optional>,...</optional>

<phrase>and <replaceable>paramspec</replaceable> is:</phrase>

<replaceable>name</replaceable>=<replaceable>value</replaceable><optional>&amp;...</optional>

</synopsis>

</para>

port component, in a single URI. A URI of the form

<literal>postgresql://host1:port1,host2:port2,host3:port3/</literal>

is equivalent to a connection string of the form

<literal>host=host1,host2,host3 port=port1,port2,port3</literal>. Each

<literal>host=host1,host2,host3 port=port1,port2,port3</literal>.

As further described below, each

host will be tried in turn until a connection is successfully established.

</para>

</sect3>

<para>

It is possible to specify multiple hosts to connect to, so that they are

tried in the given order. In the Keyword/Value format, the <literal>host</literal>,

<literal>hostaddr</literal>, and <literal>port</literal> options acceptacomma-separated

list of values. The same number of elements must be given in each

<literal>hostaddr</literal>, and <literal>port</literal> options accept comma-separated

lists of values. The same number of elements must be given in each

option that is specified, such

that e.g., the first <literal>hostaddr</literal> corresponds to the first host name,

the second <literal>hostaddr</literal> corresponds to the second host name, and so

<para>

In the connection URI format, you can list multiple <literal>host:port</literal> pairs

separated by commas, in the <literal>host</literal> component of the URI.

separated by commas in the <literal>host</literal> component of the URI.

</para>

<para>