Bug 208359 - spurious AAAA DNS query hurts performance and is anti-social
Summary: spurious AAAA DNS query hurts performance and is anti-social
Alias: None
Product: Fedora
Classification: Fedora
Component: exim
Version: 8
Hardware: All
OS: Linux
Target Milestone: ---
Assignee: David Woodhouse
QA Contact: Fedora Extras Quality Assurance
Whiteboard: bzcl34nup
Keywords: Reopened
Depends On:
TreeView+ depends on / blocked
Reported: 2006-09-28 00:19 UTC by Russell Coker
Modified: 2009-01-09 06:59 UTC (History)
2 users (show)

Clone Of:
Last Closed: 2009-01-09 06:59:09 UTC

Attachments (Terms of Use)

Description Russell Coker 2006-09-28 00:19:13 UTC
I am currently benchmarking mail relay systems with a soon to be released 
version of my Postal benchmark and found a performance related bug in 

IP exim.35992 > DNS.domain:  43702+ MX? a0.example.com. (32)
IP exim.35992 > DNS.domain:  7866+ AAAA? mail.a0.example.com. (37)
IP exim.35992 > DNS.domain:  31399+ A? mail.a0.example.com. (37)

I noticed that often DNS queries are a bottleneck.  Exim does the above 
queries for an email addressed to user@a0.example.com, however my machine has 
IPv6 disabled (the ipv6 kernel module is not loaded) so it is impossible for 
Exim to do anything with the AAAA record.  I believe that Exim should be able 
to work this out and refrain from doing the extra query.

When an entry in /etc/aliases expands to 254 users in different domains 
Postfix will do ~500 DNS queries and Exim will do ~750.  This will give Exim 
33% less performance than Postfix in some situations and will also make it 
less friendly to the network at large.

Comment 1 David Woodhouse 2006-09-28 05:41:22 UTC
See http://www.exim.org/exim-html-4.62/doc/html/spec_html/ch13.html#id2569429
for instructions on disabling all IPv6 support including AAAA lookups.

But yes, I agree that if we have no IPv6 support (in fact, I'd go so far as to
say if we have no non-link-local IPv6 addresses), Exim should probably do that

Comment 2 Bug Zapper 2008-04-04 03:52:18 UTC
Fedora apologizes that these issues have not been resolved yet. We're
sorry it's taken so long for your bug to be properly triaged and acted
on. We appreciate the time you took to report this issue and want to
make sure no important bugs slip through the cracks.

If you're currently running a version of Fedora Core between 1 and 6,
please note that Fedora no longer maintains these releases. We strongly
encourage you to upgrade to a current Fedora release. In order to
refocus our efforts as a project we are flagging all of the open bugs
for releases which are no longer maintained and closing them.

If this bug is still open against Fedora Core 1 through 6, thirty days
from now, it will be closed 'WONTFIX'. If you can reporduce this bug in
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Thanks for your help, and we apologize again that we haven't handled
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The process we are following is outlined here:

We will be following the process here:
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Comment 3 Bug Zapper 2008-05-06 16:25:34 UTC
This bug is open for a Fedora version that is no longer maintained and
will not be fixed by Fedora. Therefore we are closing this bug.

If you can reproduce this bug against a currently maintained version of
Fedora please feel free to reopen thus bug against that version.

Thank you for reporting this bug and we are sorry it could not be fixed.

Comment 4 Russell Coker 2008-05-07 00:53:54 UTC
Below is the tcpdump output from using a machine named "test" (which has the 
name "TEST" in tcpdump output) using a machine named "DNSSERVER" for it's DNS.  
I send myself an email, it does two "AAAA" lookups for itself (doing two 
lookups is a bug in itself) and then an "AAAA" lookup for my machine 
nospam.coker.com.au.  At the bottom of this report there is the ifconfig 
output showing that the machine in question has no IPv6 addresses and 
therefore no possibility of ever sending mail via IPv6.  I can only wonder 
what it might do if it was to get a response to one of it's AAAA requests.

This is from exim-4.68-1.fc8.

10:48:25.789466 IP TEST.filenet-nch > DNSSERVER.domain: 65297+ AAAA? test. 
10:48:25.790795 IP DNSSERVER.domain > TEST.filenet-nch: 65297 NXDomain 0/1/0 
10:48:25.822382 IP TEST.filenet-nch > DNSSERVER.domain: 37395+ AAAA? test. 
10:48:25.823566 IP DNSSERVER.domain > TEST.filenet-nch: 37395 NXDomain 0/1/0 
10:48:25.827032 IP TEST.filenet-nch > DNSSERVER.domain: 36442+ MX? 
coker.com.au. (30)
10:48:25.828610 IP DNSSERVER.domain > TEST.filenet-nch: 36442 1/2/3 MX[|
10:48:25.829319 IP TEST.filenet-nch > DNSSERVER.domain: 64716+ AAAA? 
nospam.sws.net.au. (35)
10:48:25.830459 IP DNSSERVER.domain > TEST.filenet-nch: 64716 0/1/0 (79)
10:48:25.831066 IP TEST.filenet-nch > DNSSERVER.domain: 4689+ A? 
nospam.sws.net.au. (35)
10:48:25.832517 IP DNSSERVER.domain > TEST.filenet-nch: 4689 1/2/2 A (132)

eth0      Link encap:Ethernet  HWaddr 00:02:A5:DE:52:B6
          inet addr:  Bcast:  Mask:
          RX packets:386 errors:0 dropped:0 overruns:0 frame:0
          TX packets:312 errors:0 dropped:0 overruns:0 carrier:0
          collisions:0 txqueuelen:1000
          RX bytes:37928 (37.0 KiB)  TX bytes:39671 (38.7 KiB)

lo        Link encap:Local Loopback
          inet addr:  Mask:
          UP LOOPBACK RUNNING  MTU:16436  Metric:1
          RX packets:1435 errors:0 dropped:0 overruns:0 frame:0
          TX packets:1435 errors:0 dropped:0 overruns:0 carrier:0
          collisions:0 txqueuelen:0
          RX bytes:3445452 (3.2 MiB)  TX bytes:3445452 (3.2 MiB)

Comment 6 Bug Zapper 2008-11-26 07:02:05 UTC
This message is a reminder that Fedora 8 is nearing its end of life.
Approximately 30 (thirty) days from now Fedora will stop maintaining
and issuing updates for Fedora 8.  It is Fedora's policy to close all
bug reports from releases that are no longer maintained.  At that time
this bug will be closed as WONTFIX if it remains open with a Fedora 
'version' of '8'.

Package Maintainer: If you wish for this bug to remain open because you
plan to fix it in a currently maintained version, simply change the 'version' 
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The process we are following is described here: 

Comment 7 Bug Zapper 2009-01-09 06:59:09 UTC
Fedora 8 changed to end-of-life (EOL) status on 2009-01-07. Fedora 8 is 
no longer maintained, which means that it will not receive any further 
security or bug fix updates. As a result we are closing this bug.

If you can reproduce this bug against a currently maintained version of 
Fedora please feel free to reopen this bug against that version.

Thank you for reporting this bug and we are sorry it could not be fixed.

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