[Bug nscd/6812] New: nscd doesn't handle temporary resolver errors properly

[Bug nscd/6812] New: nscd doesn't handle temporary resolver errors properly

[jsembera at suse dot cz]

When getnameinfo() gets temporary error from nss, it should return temporary
error instead of permanent error to the application. This has already been
solved by following patch for cases without nscd running: 

http://sourceware.org/cgi-bin/cvsweb.cgi/libc/inet/getnameinfo.c.diff?r1=1.34&r2=1.35&cvsroot=glibc&f=h

However, with nscd it still doesn't return proper value. We hit this with 2.4
first and verified that it still exists in 2.8. I have working fix for 2.4 and
unverified fix for current CVS (underlying code is a bit different). I'll attach
it in this bug.

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           Summary: nscd doesn't handle temporary resolver errors properly
           Product: glibc
           Version: unspecified
            Status: NEW
          Severity: normal
          Priority: P2
         Component: nscd
        AssignedTo: drepper at redhat dot com
        ReportedBy: jsembera at suse dot cz
                CC: glibc-bugs at sources dot redhat dot com


http://sourceware.org/bugzilla/show_bug.cgi?id=6812

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[Bug nscd/6812] nscd doesn't handle temporary resolver errors properly

[jsembera at suse dot cz]

------- Additional Comments From jsembera at suse dot cz  2008-08-01 10:02 -------
Created an attachment (id=2883)
 --> (http://sourceware.org/bugzilla/attachment.cgi?id=2883&action=view)
nscd patch for current CVS


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[Bug nscd/6812] nscd doesn't handle temporary resolver errors properly

[jsembera at suse dot cz]

------- Additional Comments From jsembera at suse dot cz  2008-08-01 10:16 -------
Created an attachment (id=2884)
 --> (http://sourceware.org/bugzilla/attachment.cgi?id=2884&action=view)
just for reference - working, verified patch that applies to 2.4


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[Bug nscd/6812] nscd doesn't handle temporary resolver errors properly

[pasky at suse dot cz]

-- 
           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |pasky at suse dot cz


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[Bug nscd/6812] nscd doesn't handle temporary resolver errors properly

[jsembera at suse dot cz]

------- Additional Comments From jsembera at suse dot cz  2010-04-15 12:34 -------
... ping?

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[Bug nscd/6812] nscd doesn't handle temporary resolver errors properly

[pasky at suse dot cz]

------- Additional Comments From pasky at suse dot cz  2010-06-01 02:18 -------
Created an attachment (id=4826)
 --> (http://sourceware.org/bugzilla/attachment.cgi?id=4826&action=view)
updated patch for HEAD


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[Bug nscd/6812] nscd doesn't handle temporary resolver errors properly

[drepper at redhat dot com]

------- Additional Comments From drepper at redhat dot com  2010-08-23 20:24 -------
I don't like this patch.  It does no caching at all.  It is highly unlikely that
a request will succeed a very short while afterwards.  Whther negtimeout is
sufficient to use is another question.  Maybe a third timeout value is needed. 
But the patch as-is is no good.

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[Bug nscd/6812] nscd doesn't handle temporary resolver errors properly

[pasky at suse dot cz]

------- Additional Comments From pasky at suse dot cz  2010-08-26 23:00 -------
I do not think it is appropriate on two counts.

First, caching temporary results would not be specific to this cache and would
be a completely orthogonal nscd-wide change, so I do not think the patch should
be judged based on this at all.

Second, the idea of caching intermittent failures itself seems strange to me.
The situation itself should happen only in relatively exceptional cases, usually
due to some network outage - in that case, it is not clear the benefit of giving
quicker feedback to the application outweights the disadvantage of prolonging
service outages or even massively amplifying mere singular errors. After all,
the return code specifically says "try again", and it is quite plausible the
application will go to some limited loop where it tries to re-resolve after very
short interval.

In short, I am worried about the amplification of singular failures, and noone
showed up so far who would actually want to cache intermittent failures to cater
for some plausible scenario.

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[Bug nscd/6812] nscd doesn't handle temporary resolver errors properly

[drepper at redhat dot com]

------- Additional Comments From drepper at redhat dot com  2010-09-13 18:45 -------
(In reply to comment #6)
> I do not think it is appropriate on two counts.
> [...]

But you're wrong.  The whole point of nscd is to reduce load and latency.  These
errors, when they happen, usually happen for some time.  And if one lookup
happens a second often follows shortly.  Caching these types of errors is
definitely the right thing to do.


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[Bug nscd/6812] nscd doesn't handle temporary resolver errors properly

[pasky at suse dot cz]

------- Additional Comments From pasky at suse dot cz  2010-09-21 14:00 -------
Ok, what you say also makes sense; however, that means I'd be wrong just on the
second count - I still believe fixing hstcache bug returning wrong results for
temporary errors is independent from implementing a new feature for general
caching of the temporary errors.

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