From c1f743ab2e4a7046d5500875a47d1f62c8624603 Mon Sep 17 00:00:00 2001 From: Daniel Baumann Date: Mon, 8 Apr 2024 22:37:50 +0200 Subject: Adding upstream version 5.7.1. Signed-off-by: Daniel Baumann --- lib/cache/README.rst | 69 ++++++++++++++++++++++++++++++++++++++++++++++++++++ 1 file changed, 69 insertions(+) create mode 100644 lib/cache/README.rst (limited to 'lib/cache/README.rst') diff --git a/lib/cache/README.rst b/lib/cache/README.rst new file mode 100644 index 0000000..767c4c0 --- /dev/null +++ b/lib/cache/README.rst @@ -0,0 +1,69 @@ +.. SPDX-License-Identifier: GPL-3.0-or-later + +.. _cache_sizing: + +Cache sizing +------------ + +For personal use-cases and small deployments cache size around 100 MB is more than enough. + +For large deployments we recommend to run Knot Resolver on a dedicated machine, and to allocate 90% of machine's free memory for resolver's cache. + +For example, imagine you have a machine with 16 GB of memory. +After machine restart you use command ``free -m`` to determine amount of free memory (without swap): + +.. code-block:: bash + + $ free -m + total used free + Mem: 15907 979 14928 + +Now you can configure cache size to be 90% of the free memory 14 928 MB, i.e. 13 453 MB: + +.. code-block:: lua + + -- 90 % of free memory after machine restart + cache.size = 13453 * MB + +.. _cache_persistence: + +Cache persistence +----------------- +.. tip:: Using tmpfs for cache improves performance and reduces disk I/O. + +By default the cache is saved on a persistent storage device +so the content of the cache is persisted during system reboot. +This usually leads to smaller latency after restart etc., +however in certain situations a non-persistent cache storage might be preferred, e.g.: + + - Resolver handles high volume of queries and I/O performance to disk is too low. + - Threat model includes attacker getting access to disk content in power-off state. + - Disk has limited number of writes (e.g. flash memory in routers). + +If non-persistent cache is desired configure cache directory to be on +tmpfs_ filesystem, a temporary in-memory file storage. +The cache content will be saved in memory, and thus have faster access +and will be lost on power-off or reboot. + + +.. note:: In most of the Unix-like systems ``/tmp`` and ``/var/run`` are commonly mounted to tmpfs. + While it is technically possible to move the cache to an existing + tmpfs filesystem, it is *not recommended*: The path to cache is specified in + multiple systemd units, and a shared tmpfs space could be used up by other + applications, leading to ``SIGBUS`` errors during runtime. + +Mounting the cache directory as tmpfs_ is recommended approach. +Make sure to use appropriate ``size=`` option and don't forget to adjust the +size in the config file as well. + +.. code-block:: + + # /etc/fstab + tmpfs /var/cache/knot-resolver tmpfs rw,size=2G,uid=knot-resolver,gid=knot-resolver,nosuid,nodev,noexec,mode=0700 0 0 + +.. code-block:: lua + + # /etc/knot-resolver/config + cache.size = 2 * GB + +.. _tmpfs: https://en.wikipedia.org/wiki/Tmpfs -- cgit v1.2.3