[rsyslog] DNS cache and expiration

[Rainer Gerhards]

> -----Original Message-----
> From: rsyslog-bounces at lists.adiscon.com 
> [mailto:rsyslog-bounces at lists.adiscon.com] On Behalf Of david at lang.hm
> Sent: Thursday, October 01, 2009 9:26 PM
> To: rsyslog-users
> Subject: Re: [rsyslog] DNS cache and expiration
> 
> On Thu, 1 Oct 2009, Rainer Gerhards wrote:
> 
> > I have now reviewed the discussion in depth. Many thanks 
> for all the good
> > thoughts.
> >
> > I will now first begin to move the name resolution calls to 
> the "backend"
> > threads (away from the inputs). However, I will create an 
> option that the
> > name resolution may be done before enqueing the message, 
> which may be used by
> > some folks for whatever reason (plus, it is trivially to 
> do). I also think I
> > will leave in the capability that inputs do the name 
> resolution themselfs, at
> > least if they prefer. For example, imuxsock always has the 
> local host as
> > input, so it makes limited sense to do name resolution 
> calls for messages
> > received from that input. Similarly, imtcp uses the name 
> that was (once)
> > obtained when the session was created (btw, this is also 
> some expiry-less
> > "name resolution", but I think here it is even harder to 
> argue against it
> > ;)).
> 
> on note on this, if you can delay the resolution to the point where 
> something actually accesses the property that uses the name 
> you may be 
> able to skip doing name resolution entirely in many cases.

This I plan to do, but in the TCP case I think it probably is better to do a
name resolution once per *session* even if the name may never be used.
Typically, there are many messages in a session and the overhead if the one
name lookup does not really matter. At least this is my current thinking.

Rainer