doc: add information about persistent timers

doc/configuration.rst

@@ -106,7 +106,11 @@ See :ref:`keys`::
       }
     }
 
-As of now it is not possible to associate multiple keys with a remote.
+
+If Knot DNS is compiled with the LMDB library, the server will be able to
+preserve slave zone timers across full server restarts. The zone expire,
+refresh, and flush timers are stored in a file-backed database in the
+:ref:`storage` directory in the ``timers`` subdirectory.
 
 Master configuration
 ====================

doc/installation.rst

@@ -36,11 +36,16 @@ Knot DNS requires few libraries to be compiled:
 * zlib
 * Userspace RCU, at least 0.5.4
 * libcap-ng, at least 0.6.4 (optional library)
+* lmdb (optional library)
 
-If libcap-ng library is available, Knot DNS will take advantage of the
+If the libcap-ng library is available, Knot DNS will take advantage of the
 POSIX 1003.1e capabilites(7) by sandboxing the exposed threads.  Most
 rights are stripped from the exposed threads for security reasons.
 
+If the LMDB library is available, the server will be able to store timers
+for slave zones in file-backed storage and the timers will persist across
+server restarts.
+
 You can probably find OpenSSL and zlib libraries already included in
 your system or distribution.  If not, zlib resides at http://zlib.net,
 and OpenSSL can be found at http://www.openssl.org.

doc/introduction.rst

@@ -41,6 +41,7 @@ Server features:
 * Reconfiguring server instance on-the-fly
 * IPv4 / IPv6 support
 * Semantic checks of zones
+* Persistent zone timers
 
 For more info and downloads see `www.knot-dns.cz <https://www.knot-dns.cz>`_.