<term><literal>target_session_attrs</literal></term>

<listitem>

<para>

If this parameter is set to <literal>read-write</literal>, only a

connection in which read-write transactions are accepted by default

is considered acceptable. The query

<literal>SHOW transaction_read_only</literal> will be sent upon any

successful connection; if it returns <literal>on</literal>, the connection

will be closed. If multiple hosts were specified in the connection

string, any remaining servers will be tried just as if the connection

attempt had failed. The default value of this parameter,

<literal>any</literal>, regards all connections as acceptable.

</para>

This option determines whether the session must have certain

properties to be acceptable. It's typically used in combination

with multiple host names to select the first acceptable alternative

among several hosts. There are six modes:

<variablelist>

<varlistentry>

<term><literal>any</literal> (default)</term>

<listitem>

<para>

any successful connection is acceptable

</para>

</listitem>

</varlistentry>

<varlistentry>

<term><literal>read-write</literal></term>

<listitem>

<para>

session must accept read-write transactions by default (that

is, the server must not be in hot standby mode and

the <varname>default_transaction_read_only</varname> parameter

must be <literal>off</literal>)

</para>

</listitem>

</varlistentry>

<varlistentry>

<term><literal>read-only</literal></term>

<listitem>

<para>

session must not accept read-write transactions by default (the

converse)

</para>

</listitem>

</varlistentry>

<varlistentry>

<term><literal>primary</literal></term>

<listitem>

<para>

server must not be in hot standby mode

</para>

</listitem>

</varlistentry>

<varlistentry>

<term><literal>standby</literal></term>

<listitem>

<para>

server must be in hot standby mode

</para>

</listitem>

</varlistentry>

<varlistentry>

<term><literal>prefer-standby</literal></term>

<listitem>

<para>

first try to find a standby server, but if none of the listed

hosts is a standby server, try again in <literal>all</literal>

mode

</para>

</listitem>

</varlistentry>

</variablelist>

</para>

</listitem>

</varlistentry>

</varlistentry>

</variablelist>

</para>

</sect2>