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Combination of edge cases triggers ~200ms delay in TTFB
10-28-2014, 05:39 AM
Post: #15
RE: Combination of edge cases triggers ~200ms delay in TTFB
I've been running ( LOTS ) more tests against our private instance to narrow this down more.

After trying several different options I settled with adding "gzip_min_length 1603;" to the Nginx config. I was able to get a better TTFB for both of my initial tests:

- http://www.webpagetest.org/result/141027...13bc3570d/
- http://www.webpagetest.org/result/141027...9d1c88b53/

I've got another test that looks like requesting two resources. That ran into the same ~200ms TTFB delay as well, even with "gzip_min_length 1603;" set. The second request was not delayed, even though it was also for a very small file.

In the two request case it came down to the first request being less than 1,009 bytes triggering the delay:

- 2 req, 1008 byte 1st (delay): http://www.webpagetest.org/result/141027...f274fbf14/
- 2 req, 1009 byte 1st (no delay): http://www.webpagetest.org/result/141027...2c90c83ae/

I tried shrinking small.html by a few bytes and increasing small.css by the same amount. Still triggered the delay: http://www.webpagetest.org/result/141027...b181a2fb8/

The first request still appears to be the key here. And the 1603 limit isn't sufficient, because files below 1,009 bytes also triggered the delay.

At this point it looks like we could avoid the delay by doing the following:

- Add "gzip_min_length 1603;" to Nginx config
- Make sure all files are 1,009 bytes or more

At best these are hacky work arounds. And I'm not even 100% sure if 1,603 and 1,009 are consistent points, or just artifacts of my particular test setup.
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RE: Combination of edge cases triggers ~200ms delay in TTFB - josephscott - 10-28-2014 05:39 AM

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