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Test tools variance speed results
11-25-2015, 03:07 AM
Post: #2
RE: Test tools variance speed results
Pingdom is expected to be radically different because they don't apply any traffic shaping. Historically they also haven't used real browsers but I'm not sure if that's still the case (their UA string looks like Chrome 39).

As far as GTMetrix goes, I'm not sure what is going on with their test but the traffic shaping doesn't look to be working correctly (though it may be close). Some quick back-of-the-napkin numbers using the 2.14MB total bytes they recorded and 5Mbps connection profile:

2.14 MB * 8 bits per byte * 1024 KB per MB * 1024 B per KB = 17,951,621 bits
5 Mbps * 1000000 / 1.026 (2.6% TCP overhead) = 4,873,294 bits per second
17,951,621 / 4,873,294 = 3.68s

So, on a perfectly warm connection with no round trip delays of any kind it would take ~3.7 seconds to transfer the 2.14MB of page data. 2.9s isn't physically possible. There's a few hundred ms of round trip times waiting for the first byte and also TCP slow start so 4-5 seconds on a 5Mbps connection looks about right.
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RE: Test tools variance speed results - pmeenan - 11-25-2015 03:07 AM

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