Unbound cache hit rate is anaemic

johnpoz

Well your really going to need to look to what is being looked up, and you might want to adjust your min TTL, as stated before many a ttl this days is just so freaking low - for no reason I can see other than trying to up their query count.

The only sane reason you would have a 5 minute or 60 second ttl, if you were in the middle of migration.. A round robin of 1 hour or 8 hours works just the same as a round robin with 5 minutes.. Your still spreading the load across those IPs.. And with many things pointing to a CDN which is behind load balancing anyway..

The only reason I can see for such low ttls, is wanting to inflate the number of queries so you can charge more ;)

stevogas

@johnpoz said in Unbound cache hit rate is anaemic:

min TTL

Bumped to 3600. From 1200.

stevogas

Up over 69 hrs. which is an accomplishment in itself.

uptime: 216706 seconds

And 60.9% hitrate. It achieved that level after only a few hours and has been steady.

total.num.queries=58241
total.num.queries_ip_ratelimited=0
total.num.cachehits=35473
total.num.cachemiss=22768
total.num.prefetch=933
total.num.expired=0
total.num.recursivereplies=22768

Thanks @johnpoz for the suggestions! We may be at the upper limit for this config.

johnpoz

@stevogas said in Unbound cache hit rate is anaemic:

total.num.expired=0

Turn on serve 0, see if that bumps your rate up some..

chrcoluk

OP, try enabling "serve expired" option in the DNS resolver advanced settings.

This is mine with the option enabled.

root@PFSENSE ~ # unbound-control -c /var/unbound/unbound.conf stats_noreset | egrep 'total.num|cache.count'
total.num.queries=218959
total.num.queries_ip_ratelimited=0
total.num.cachehits=216339
total.num.cachemiss=2620
total.num.prefetch=28326
total.num.expired=21661
total.num.recursivereplies=2620
msg.cache.count=2333
rrset.cache.count=2034
infra.cache.count=3
key.cache.count=0

stevogas

Thank you very much @johnpoz @chrcoluk , after 24hrs cachehits are up to over 88%!

total.num.queries=35176
total.num.queries_ip_ratelimited=0
total.num.cachehits=31218
total.num.cachemiss=3958
total.num.prefetch=7532
total.num.expired=7027
total.num.recursivereplies=3958
msg.cache.count=4324
rrset.cache.count=3322
infra.cache.count=5
key.cache.count=0

@chrcoluk there is a big internet out there, don't keep going to the same sites everyday! (98%, wow).

johnpoz

@stevogas said in Unbound cache hit rate is anaemic:

total.num.expired=7027

So you must be hitting sites less than once an hour even if have min ttl set to 3600, but you have that many hits on serving expired entries.

Doing stats on what is asked for, how often, what the normal ttls are, how often you query - from what your doing the queries from How many users you have.. It can become a obsessive past time ;)

While normal, old school practice was to never mess with ttls, and serving up expired could be problematic - depending on what is being asked for.. But to be honest - these companies have decided that a ttl of 60 or 300 seconds is fine... Which is BS if you ask me.. Unless what your looking for is user data.. Really how often is the IP of some fqdn going to change??? So what is the point of having the client have to look it up 60 seconds later?

Much of the net is served up by CDNs, much if it anycast to allow for global networks and use of the same IP, etc. You can not serve the public with 1 or 2 IPs assigned to a couple of servers - so your behind some load balancing system, with hundreds if not 1000s of servers serving the content from a pool, etc.

So you setup some IPs on the front end of your load balancing - how often would those change? So what is the point of a 60 or 300 second ttl? To lower the amount of queries - those ttls should be getting longer, not shorter.. But hey then we wont know how often somebody wants to go to some fqdn.. And hey company X pays for dns by number of queries they are getting.. So why not have them query way more than they need too ;)

I have not run into any issues that I am aware of by setting min ttl, or serving expired. Here is the thing - even when unbound serves up expired.. the ttl on that is 0.. So while your client will try and go to that IP.. If for whatever reason it fails (ip changed) and you try and go there again, unbound in the background has looked up that record again - and would now have the new IP if it changed, etc.

DNS is a fascinating protocol, and the deeper you get into it - the more interesting it becomes.

Have fun!

tomashk

And if somebody is afraid about serving expired you can always put the following into custom options:

server:
serve-expired-ttl: 86400

stevogas

Over 38 hours and hitting 91%.

total.num.queries=65336
total.num.queries_ip_ratelimited=0
total.num.cachehits=59497
total.num.cachemiss=5839
total.num.prefetch=14832
total.num.expired=13774
total.num.recursivereplies=5839
msg.cache.count=6355
rrset.cache.count=4728
infra.cache.count=5
key.cache.count=0

chrcoluk

@tomashk said in Unbound cache hit rate is anaemic:

And if somebody is afraid about serving expired you can always put the following into custom options:
server:
serve-expired-ttl: 86400

Yep, it can be fine tuned now.

I will present two scenarios, both will be rare in practice, but possible.

Scenario - A content provider changes ip for its services, old ip is dead.

You the user has boosted ttl to 3600 via minttl, and the change happened after 20 mins of the ttl so about another 40 minutes, you hit refresh when the page fails to load and it will be broken for another 40 minutes or until dns cache is flushed.

However if you used serve expired, you would get an initial page load failure, but on refresh it will work as in the background the cache got refreshed.

So whilst both dont comply with the ttl records, serve expired is much more elegant.

In practice this will be rare, and you will just get much higher cache hit rates.

I do agree with John that modern extremely low ttl dns practice is stupid, I am pretty sure that breaks the original RFC as well, it used to be to only set that low if you moving content to another ip, but then increase again after. This is why I pushed for serve expired to be added to the pfsense UI.

johnpoz

@chrcoluk said in Unbound cache hit rate is anaemic:

it used to be to only set that low if you moving content to another ip

Yup use to do that all the time back in the day... As you got closer and closer to zero hour for the switch you would lower the in steps.. Lets say you had a ttl of 24 hours... Couple of days before you might change it to 12.. hours, then 6 later and then 3 later, until you were down to say 1 minute.. for a short time before zero hour.. You would then change your IP.. And within 1 minute everyone should be using the new IP.. Then you could ramp it back up.. Again in steps - just in case you find out something not working and you need to change it.. You wouldn't want some clients having grabbed your 24 hour ttl, etc..

You would ramp down vs just jumping down because that could cause a huge spike on your dns traffic, if you moved it down slowly it would prevent a spike in your dns queries so you were sure you could handle the number of queries with the shorter ttl, etc.