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DNS Look up + Time to first byte
07-31-2014, 12:24 AM
Post: #1
DNS Look up + Time to first byte
I have a problem with long DNS Look up + Time to first byte on the URL it self.

I'm getting mixed results. Please see below:

DNS Lookup: 4 ms + Time to First Byte: 44 ms
http://www.webpagetest.org/result/140730_BV_N8J/

DNS Lookup: 3129 ms + Time to First Byte: 1714 ms
http://www.webpagetest.org/result/140730_QH_KT1/

I have talked to the hosting company and the domain registrar. The hosting company says that everything looks good from their side. Domain registrar blames the hosting company.

What do you guys think? Thanks a lot!
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07-31-2014, 07:41 PM
Post: #2
RE: DNS Look up + Time to first byte
As far as I know WPT won't tell you the nameserver that was used to process your DNS query.

According to dig, your domain has 5 name servers configured:

$ dig ns +short rabattkodsjakten.se | sort
ns3.binero.se.
ns4.binero.se.
ns5.binero.se.
ns6.binero.se.
ns7.binero.se.

I've created a simple script to run 10 queries for your domain against each of the nameserver above and it seems like their performance vary a lot:

$ (echo ns{3..7}.binero.se; for i in {1..10}; do for NAMESERVER in ns{3..7}.binero.se; do (time dig +time=3 +tries=1 rabattkodsjakten.se @${NAMESERVER}) 2>&1 | grep real | awk '{print $2}'; done | xargs ; done ) | column -t

ns3.binero.se ns4.binero.se ns5.binero.se ns6.binero.se ns7.binero.se
0m4.011s 0m0.020s 0m4.012s 0m0.020s 0m0.044s
0m4.010s 0m0.019s 0m0.264s 0m0.019s 0m0.043s
0m0.261s 0m0.019s 0m4.012s 0m0.020s 0m0.043s
0m4.013s 0m0.019s 0m0.268s 0m0.019s 0m0.042s
0m4.014s 0m0.018s 0m4.012s 0m0.017s 0m0.045s
0m4.013s 0m0.018s 0m4.012s 0m0.021s 0m0.046s
0m4.011s 0m0.019s 0m4.011s 0m0.020s 0m0.043s
0m4.011s 0m0.020s 0m0.266s 0m0.019s 0m0.043s
0m4.012s 0m0.020s 0m4.014s 0m0.019s 0m0.044s
0m4.012s 0m0.019s 0m4.012s 0m0.019s 0m0.042s

ns4, ns6 and ns7 responded all 3 queries in less than 50ms which is very good.
ns3 and ns5 however, timed out on almost all queries (ns5 answered 2 queries in 200ms which is still significantly above the others)

I believe the slow DNS results you are getting are from tests using ns3 and ns5.

Get in touch with your ISP and ask them to have a look at nameserver ns3.binero.se and ns5.binero.se

On a side note, I've found on the chromium source code that the browser DNS timeout is 5 seconds:
https://chromium.googlesource.com/chromi...session.cc
const unsigned kMaxTimeoutMs = 5000;

However I could not find if it makes multiple requests in parallel or the number or DNS retries.

Regarding the slow time to first byte then you would need to have a look at your application logs to understand what exactly it was trying to do and why it took so long.
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