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Doc: improve discussion of reverse+forward host name lookup in pg_hba.conf.
Fix some grammatical issues and make it a bit more readable.
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@ -275,7 +275,7 @@ hostnossl <replaceable>database</replaceable> <replaceable>user</replaceable>
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<para>
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<para>
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If a host name is specified (anything that is not an IP address
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If a host name is specified (anything that is not an IP address
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or a special key word is processed as a potential host name),
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or a special key word is treated as a host name),
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that name is compared with the result of a reverse name
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that name is compared with the result of a reverse name
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resolution of the client's IP address (e.g., reverse DNS
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resolution of the client's IP address (e.g., reverse DNS
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lookup, if DNS is used). Host name comparisons are case
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lookup, if DNS is used). Host name comparisons are case
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@ -310,22 +310,28 @@ hostnossl <replaceable>database</replaceable> <replaceable>user</replaceable>
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the client's host name instead of the IP address in the log.
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the client's host name instead of the IP address in the log.
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</para>
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</para>
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<para>
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This field only applies to <literal>host</literal>,
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<literal>hostssl</literal>, and <literal>hostnossl</> records.
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</para>
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<sidebar>
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<sidebar>
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<para>
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<para>
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Occasionally, users have wondered why host names are handled
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Users sometimes wonder why host names are handled
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in this seemingly complicated way with two name resolutions
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in this seemingly complicated way, with two name resolutions
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and requiring reverse lookup of IP addresses, which is
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including a reverse lookup of the client's IP address. This
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sometimes not set up or points to some undesirable host name.
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complicates use of the feature in case the client's reverse DNS
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It is primarily for efficiency: A connection attempt requires
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entry is not set up or yields some undesirable host name.
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two resolver lookups of the current client's address. If
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It is done primarily for efficiency: this way, a connection attempt
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there is resolver problem with that address, it becomes only
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requires at most two resolver lookups, one reverse and one forward.
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If there is a resolver problem with some address, it becomes only
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that client's problem. A hypothetical alternative
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that client's problem. A hypothetical alternative
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implementation which only does forward lookups would have to
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implementation that only did forward lookups would have to
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resolve every host name mentioned in
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resolve every host name mentioned in
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<filename>pg_hba.conf</filename> at every connection attempt.
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<filename>pg_hba.conf</filename> during every connection attempt.
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That would already be slow by itself. And if there is a
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That could be quite slow if many names are listed.
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resolver problem with one of the host names, it becomes
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And if there is a resolver problem with one of the host names,
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everyone's problem.
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it becomes everyone's problem.
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</para>
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</para>
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<para>
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<para>
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@ -340,11 +346,6 @@ hostnossl <replaceable>database</replaceable> <replaceable>user</replaceable>
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Apache HTTP Server and TCP Wrappers.
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Apache HTTP Server and TCP Wrappers.
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</para>
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</para>
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</sidebar>
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</sidebar>
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<para>
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This field only applies to <literal>host</literal>,
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<literal>hostssl</literal>, and <literal>hostnossl</> records.
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</para>
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</listitem>
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</listitem>
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</varlistentry>
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</varlistentry>
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