Speeding up graphs with RRDCacheD

When the graphs are stored with the RRDTool engine, every IP graph update is a small random disk write. RRDCacheD batches these updates in memory and flushes them in bulk, which greatly reduces the disk I/O of the Console server.

1. Install the packages:

   apt-get install rrdtool rrdcached

2. Edit /etc/default/rrdcached and set:

   OPTS="-l unix:/var/run/rrdcached.sock -s andrisoft -m 774 -w 3600 -f 7200 -F -b /var/lib/rrdcached/db/"

3. The ownership and permissions of the socket reset on every service start, so let systemd fix them automatically: run systemctl edit rrdcached and add:

   [Service]
   ExecStartPost=/bin/sh -c "/bin/sleep 2; /bin/chown andrisoft:www-data /var/run/rrdcached.sock; /bin/chmod 770 /var/run/rrdcached.sock"

4. Enable and start the service:

   systemctl daemon-reload
   systemctl enable --now rrdcached

5. Add unix:/var/run/rrdcached.sock to the RRDCached Socket field in Configuration » General Settings » Graphs & Storage. The existing IP graphs do not need to be deleted.

1. Install RRDTool (the rrdcached daemon is included in the rrdtool package):

   dnf install rrdtool

2. Create the service file /usr/lib/systemd/system/rrdcached.service with the following content:

   [Unit]
   Description=RRDCacheD for Andrisoft
   
   [Service]
   Restart=always
   User=andrisoft
   PermissionsStartOnly=yes
   ExecStartPre=/bin/sh -c "/bin/mkdir -p /var/rrdtool/rrdcached/; /bin/chown andrisoft:andrisoft /var/rrdtool/rrdcached"
   ExecStart=/usr/bin/rrdcached -l unix:/var/rrdtool/rrdcached/rrdcached.sock -s andrisoft -m 774 -w 3600 -g -p /var/rrdtool/rrdcached/rrdcached.pid
   ExecStartPost=/bin/sh -c "/bin/sleep 4; /bin/chown andrisoft:apache /var/rrdtool/rrdcached/rrdcached.sock; /bin/chown andrisoft:andrisoft /var/rrdtool/rrdcached/rrdcached.pid; /bin/chmod 770 /var/rrdtool/rrdcached/rrdcached.sock"
   
   [Install]
   WantedBy=multi-user.target

3. Enable and start the service:

   systemctl daemon-reload
   systemctl enable --now rrdcached

4. Add unix:/var/rrdtool/rrdcached/rrdcached.sock to the RRDCached Socket field in Configuration » General Settings » Graphs & Storage. The existing IP graphs do not need to be deleted.

You can watch RRDCacheD at work with (replace the socket path on Rocky/Alma/RHEL):

while true; do clear; echo STATS | socat - /var/run/rrdcached.sock; sleep 1; done