[Pdns-users] pdns-recursor cache settings

Tomasz Kawalec kawalec.tomasz at gmail.com
Tue Feb 25 13:41:02 UTC 2014

Hello Peter,
                    thank you for quick response.  In the mean time I've 
set max-cache-entries to 4M and max-packetcache-entries to 1M with 4 
threads. If I execute `rec_control get cache-entries packetcache-entries 
negcache-entries nsspeeds-entries`

cache-entries = 4000398
packetcache-entries = 1000478
negcache-entries = 400147
nsspeeds-entries = 32238

Your answer:

"The max-*-entries settings are per thread. So, threads=4 and 
max-cache-entries=4M will yield you a total of 16M entries, but there 
will be a lot of overlap between those 4 sets!"

My questions:

1. How the packetcache, cache, negcache and nsspeeds are shared/access 
between threads. My assumption is that the is ONE packetcache, ONE cache 
etc. regardless to number of threads that are set. Further these caches 
are shared between threads. With those assumptions I think the 
rec_control output should report ~16M entries not 4M for cache-entries.
2. What do you mean by overlapping? Could you explain on some kind of 

About the recommendations for cache settings => I try different sets of 
values for cache and packetcache entries but I need to know how many 
instances of each type of cache exists (connected to number of threads). 
The is a different story if:

1. All threads share the same instance of each cache.
2. Each thread has its own instance of each cache.

If the second answer is true I think it is not optimal to set many 
threads. Another question that came into my mind is: if I set number of 
threads to 4 and I've 8 CPU sockets visible from the system point of 
view - will those 2 threads  use all of the available CPU sockets or 
each thread will use only on CPU socket.
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