High Performance Web Sites memo(1)

High Performance Web Sites
Chapter A: The Importance of Frontend Performance

The first bar, labeled html, is the initial request for the HTML document.The
browser parses the HTML and starts downloading the components in the page

The HTML document is only 5% of the total response time.The user spends
most of the other 95% waiting for the components to download; she also spends a
small amount of time waiting for HTML, scripts, and stylesheets to be parsed, as
shown by the blank gaps between downloads.

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One redirect ????
One cached image , conditional GET request

the HTTP status codes and headers
affect the browser’s cache

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you can see a blank space with no downloads that occurs immediately
following the HTML document’s HTTP request.This is time when the browser
is parsing HTML, JavaScript, and CSS, and retrieving components from its
cache

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there are as many as six or seven simultaneous HTTP requests.This behavior is due to the
number of different hostnames being used, and whether they use HTTP/1.0 or
HTTP/1.1

Parallel requests don't happen during requests for scripts.That's because in
most situations, browsers block additional HTTP requests while they download
scripts.