6. Statistics

The rec_control get command can be used to query the following statistics, either single keys or multiple statistics at once:

all-outqueries      counts the number of outgoing UDP queries since starting
answers0-1          counts the number of queries answered within 1 millisecond
answers100-1000     counts the number of queries answered within 1 second
answers10-100       counts the number of queries answered within 100 milliseconds
answers1-10         counts the number of queries answered within 10 milliseconds
answers-slow        counts the number of queries answered after 1 second
cache-bytes         Size of the cache in bytes (since 3.3.1)
cache-entries       shows the number of entries in the cache
cache-hits          counts the number of cache hits since starting
cache-misses        counts the number of cache misses since starting
chain-resends       number of queries chained to existing outstanding query
client-parse-errors counts number of client packets that could not be parsed
concurrent-queries  shows the number of MThreads currently running
dlg-only-drops      number of records dropped because of delegation only setting
dont-outqueries	    number of outgoing queries dropped because of 'dont-query' setting (since 3.3)
ipv6-outqueries     number of outgoing queries over IPv6
max-mthread-stack   maximum amount of thread stack ever used
negcache-entries    shows the number of entries in the Negative answer cache
noerror-answers     counts the number of times it answered NOERROR since starting
nsspeeds-entries    shows the number of entries in the NS speeds map
nsset-invalidations number of times an nsset was dropped because it no longer worked
nxdomain-answers    counts the number of times it answered NXDOMAIN since starting
outgoing-timeouts   counts the number of timeouts on outgoing UDP queries since starting
over-capacity-drops Questions dropped because over maximum concurrent query limit (since 3.2)
packetcache-bytes   Size of the packet cache in bytes (since 3.3.1)
packetcache-entries Size of packet cache (since 3.2)
packetcache-hits    Packet cache hits (since 3.2)
packetcache-misses  Packet cache misses (since 3.2)
qa-latency          shows the current latency average, in microseconds
questions           counts all End-user initiated queries with the RD bit set
ipv6-questions      counts all End-user initiated queries with the RD bit set, received over IPv6 UDP
resource-limits     counts number of queries that could not be performed because of resource limits
server-parse-errors counts number of server replied packets that could not be parsed
servfail-answers    counts the number of times it answered SERVFAIL since starting
spoof-prevents      number of times PowerDNS considered itself spoofed, and dropped the data
sys-msec            number of CPU milliseconds spent in 'system' mode
tcp-client-overflow number of times an IP address was denied TCP access because it already had too many connections
tcp-outqueries      counts the number of outgoing TCP queries since starting
tcp-questions       counts all incoming TCP queries (since starting)
throttled-out       counts the number of throttled outgoing UDP queries since starting
throttle-entries    shows the number of entries in the throttle map
unauthorized-tcp    number of TCP questions denied because of allow-from restrictions
unauthorized-udp    number of UDP questions denied because of allow-from restrictions
unexpected-packets  number of answers from remote servers that were unexpected (might point to spoofing)
uptime              number of seconds process has been running (since 3.1.5)
user-msec           number of CPU milliseconds spent in 'user' mode
	  

In the rrd/ subdirectory a number of rrdtool scripts is provided to make nice graphs of all these numbers. Use rec_control get-all to get all statistics in one go.

It should be noted that answers0-1 + answers1-10 + answers10-100 + answers100-1000 + packetcache-hits + over-capacity-drops = questions.

Every half our or so, the recursor outputs a line with statistics. More infrastructure is planned so as to allow for Cricket or MRTG graphs. To force the output of statistics, send the process a SIGUSR1. A line of statistics looks like this:

Feb 10 14:16:03 stats: 125784 questions, 13971 cache entries, 309 negative entries, 84% cache hits, outpacket/query ratio 37%, 12% throttled

This means that there are 13791 different names cached, which each may have multiple records attached to them. There are 309 items in the negative cache, items of which it is known that don't exist and won't do so for the near future. 84% of incoming questions could be answered without any additional queries going out to the net.

The outpacket/query ratio means that on average, 0.37 packets were needed to answer a question. Initially this ratio may be well over 100% as additional queries may be needed to actually recurse the DNS and figure out the addresses of nameservers.

Finally, 12% of queries were not performed because identical queries had gone out previously, saving load servers worldwide.