[master] note RPZ performance issues in ARM

diff --git a/doc/arm/Bv9ARM-book.xml b/doc/arm/Bv9ARM-book.xml
index 87da1e1108ffc15ab2181ec6d490f113a62a5e32..f8b3426cac0bdb7a663d0bf8064467dec0b616dd 100644 (file)
--- a/doc/arm/Bv9ARM-book.xml
+++ b/doc/arm/Bv9ARM-book.xml
@@ -9874,6 +9874,20 @@ bzone.domain.com        CNAME   garden.example.com.
 ns.domain.com.rpz-nsdname   CNAME   .
 48.zz.2.2001.rpz-nsip       CNAME   .
 </programlisting>
+         <para>
+            Note: RPZ may impact server performance.  Each configured
+            response policy zone requires the server to perform one to four
+            additional database lookups before a query can be answered.
+            For example, a DNS server with four policy zones, each with all
+            four kinds of response triggers &mdash; QNAME, IP, NSIP, and
+            NSDNAME &mdash; requires a total of 17 times as many database
+            lookups as a similar DNS server with no response policy zones.
+            A <acronym>BIND9</acronym> server with adequate memory and one
+            response policy zone with QNAME and IP triggers might achieve a
+            maximum queries-per-second rate about 20% lower.  A server with
+            four response policy zones with QNAME and IP triggers might
+            have a maximum QPS rate about 50% lower.
+         </para>
         </sect3>
       </sect2>