Lefteris Tsintjelis:
> On 22/6/2019 17:36, Wietse Venema wrote:
> >
> > Sharing a non-persistent cache (memcache) is the only option because
> > it can respond with low latency both for old and new queries. But
> > that of course limits the cache size.
> >
> > Sharing a persistent cache is not an option because that requires
> > a DBMS with milliscond query latency (with a query latency of 50ms,
> > one postscreen instance would handle at most 20 clients per second).
>
> DBMS would very possibly be slow for large backscatter scenarios.
>
> > You could try to combine a shared memcache and a shared persistent
> > cache, but that will only improve the best case where most connections
> > come from a limited set of clients. The memcache will not improve
> > the worst case, for example a backscatter scenario where most clients
> > are clients new. In that case the postscreen performance would be
> > exactly as bad as in the previous paragraph.
>
> Wouldn't the worst case scenario with many new clients improve also by
> reducing latency though? I suspect this has a lot to do with DNSBL
> response time(???) or maybe there are other important delay factors
> besides that? What I have in mind is a local only postscreen DNSBL and
> the 50ms can easily go down to a millisecond.
FYI, postscreen queries its cache BEFORE it decides if DNSXL checks
are needed. Therefore you can't speed up postscreen cache queries
with faster DNS.
Wietse
