document max-ixfr-ratio

diff --git a/doc/arm/Bv9ARM-book.xml b/doc/arm/Bv9ARM-book.xml
index 89c54f96542f1a3e2fc8ef5e4e5d1a80ac7a1e7d..a006816a29122c53f108a25e0e8214cea0b10b2c 100644 (file)
--- a/doc/arm/Bv9ARM-book.xml
+++ b/doc/arm/Bv9ARM-book.xml
@@ -1474,30 +1474,43 @@ controls {
 
       <para>
        The incremental zone transfer (IXFR) protocol is a way for
-       slave servers to transfer only changed data, instead of having to
+       secondary servers to transfer only changed data, instead of having to
        transfer the entire zone. The IXFR protocol is specified in RFC
        1995. See <xref linkend="proposed_standards"/>.
       </para>
 
       <para>
-       When acting as a master, <acronym>BIND</acronym> 9
+       When acting as a primary server, <acronym>BIND</acronym> 9
        supports IXFR for those zones
        where the necessary change history information is available. These
-       include master zones maintained by dynamic update and slave zones
+       include primary zones maintained by dynamic update and secondary zones
        whose data was obtained by IXFR.  For manually maintained master
-       zones, and for slave zones obtained by performing a full zone
+       zones, and for secondary zones obtained by performing a full zone
        transfer (AXFR), IXFR is supported only if the option
        <command>ixfr-from-differences</command> is set
        to <userinput>yes</userinput>.
       </para>
 
       <para>
-       When acting as a slave, <acronym>BIND</acronym> 9 will
+       When acting as a secondary server, <acronym>BIND</acronym> 9 will
        attempt to use IXFR unless
        it is explicitly disabled. For more information about disabling
        IXFR, see the description of the <command>request-ixfr</command> clause
        of the <command>server</command> statement.
       </para>
+
+      <para>
+       When a secondary server receives a zone via AXFR, it creates a
+       new copy of the zone database and then swaps it into place; during
+       the loading process, queries continue to be served from the old
+       database with no interference. When receiving a zone via IXFR,
+       however, changes are applied to the running zone, which may
+       degrade query performance during the transfer.  If a server
+       receiving an IXFR request determines that the response size would
+       be similar in size to an AXFR response, it may wish to send AXFR
+       instead. The threshold at which this determination is made can
+       be configured using the <command>max-ixfr-ratio</command> option.
+      </para>
     </section>
 
     <section xml:id="split_dns"><info><title>Split DNS</title></info>
@@ -4656,6 +4669,25 @@ badresp:1,adberr:0,findfail:0,valfail:0]
            </listitem>
          </varlistentry>
 
+         <varlistentry>
+           <term><command>max-ixfr-ratio</command></term>
+           <listitem>
+             <para>
+               Sets the size threshold (expressed as a percentage
+               of the size of the full zone) beyond which
+               <command>named</command> will choose to use an AXFR
+               response rather than IXFR when answering zone transfer
+               requests.  See <xref linkend="incremental_zone_transfers"/>.
+             </para>
+             <para>
+               The minimum value is <literal>1%</literal>. The keyword
+               <literal>unlimited</literal> disables ratio checking and
+               allows IXFRs of any size.  The default is
+               <literal>100%</literal>.
+             </para>
+           </listitem>
+         </varlistentry>
+
          <varlistentry>
            <term><command>new-zones-directory</command></term>
            <listitem>
@@ -12424,6 +12456,17 @@ view "external" {
                </listitem>
              </varlistentry>
 
+             <varlistentry>
+               <term><command>max-ixfr-ratio</command></term>
+               <listitem>
+                 <para>
+                   See the description of
+                   <command>max-ixfr-ratio</command> in
+                   <xref linkend="options"/>.
+                 </para>
+               </listitem>
+             </varlistentry>
+
              <varlistentry>
                <term><command>max-journal-size</command></term>
                <listitem>