Внедрение протокола spdy в социальной сети linkedin, omer shapira...
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SPDY at LinkedInOmer Shapira
LinkedIn Bandwidth vs. Latency Challenges with HTTP What is SPDY How LinkedIn network stack looks today How we are adopting SPDY
AgendaWhat to expect before beers
Social network for business Founded in 2002 300M+ users 200 countries Users first
Speed mattersWho we are and what we do
We measure vehicle speed in m/s
How do we measure the Internet speed?
Cars vs. trains as analogy Bandwidth vs. latency
Let’s talk about speedWhat’s speed, anyway?
Bandwidth is analogous to number of seats in a plane
Adding bandwidth is expensive – but simple
Typically sold as “speed” Matters for streaming Bandwidth does not
matter that much for business applications
Let’s talk about bandwidthOne bazzillion MBps…
Shorten the pipe Or move faster Speed of light is a hard limit Decreasing latency is hard
and sometimes impossible
Let’s talk about latencyLatency: time it takes for the server to receive and process request for a page object
100ms – user perceives as instantaneous. 1s – is about the upper limit of human flow of thought. User
loses the feeling direct feedback. 10s – upper limit of attention. Feedback is important, and the
chance of context switch is high. Source: Nielsen Norman Group
Important latency limitsNo one will advertise latency
Reality checkSignal latency in vacuum and fiber
Route Distance (km)
Time in vacuum (ms)
Time in fiber (ms)
TCP handshake in fiber (ms)
NYC to SF 4148 14 21 63
NYC to London 5585 19 28 84
NYC to Sydney 15993 53 80 240
More about network latencyNot all latencies are the same
In realityNot all latencies are the same
Fast InternetShort latencies, high bandwidth, opportunities
Low latency High bandwidth … PROFIT!
Mimics interactions between a person and a newspaper – Reading a page takes time. – Transferring text is easy– Single browser window
On a Sunday morning, with a cup of coffee
Let’s talk about HTTPLong latencies, low bandwidth, lots of client time
Hyper TEXT transfer protocolIn reality we mostly transfer images
Challenges with HTTPThe protocol is getting obsolete
Challenges with HTTP5 requests in flight, the rest wait…
Once all threads are used,
the browser blocks the next request…
Challenges with HTTPCongestion Control
Under HTTP/1.1, browser has to parse the page to get more URLs
This includes executing JS in <head> section Extra latency
Challenges with HTTPData from server
Headers are transmitted with every request But some of the headers need to be only transferred once
– Accepts-Encoding Headers are never compressed
Challenges with HTTPHeaders are never compressed
Server sent 914 bytes to
transfer 57 bytes of response.
This is 15x overhead
SPDY – a new beginning Foundations for HTTP/2
Starts with NPN negotiation (optionally as HTTP) If both server and browser support SPDY, they switch to SPDY
Overview of SPDYDrop in replacement, transparent for webdevs and SWEs
Single connection is maintained between browser and server Congestion window grows, increasing utilization of the network Unlimited resources in flight – browser is not blocked
Overview of SPDYMultiplexing instead of thread pools
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Negotiated over SSL (NPN/ALPN) or as HTTP upgrade Transport layer security (always in SPDY, optional in HTTP/2.0) Compression (including headers)
Overview of SPDYBased on SSL/TLS
23
Server can speculatively push resources to client before base page has been parsed
Resources can be reused between pages through the browser cache.
Overview of SPDYServer push
24
Explicit headers are eliminated
Headers are further compressed
Overview of SPDYHeader elimination and compression
25
Putting SPDY to work at LinkedInSo what?
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Anatomy of a pageOne base page and tons of static content
Base page
Static Content
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LinkedIn network stack Or rather non-planar graph
Distribute the content around the globe
Make the web pretty fast by shortening the pipes
CDNsBlazing fast, ubiquitous and not flexible
There is a CDN edge near you
Can we beat CDNs locally?Let’s use science to experiment!
Profile page is better across the board
Homepage is better for regions closer to ECH
Comparing SPDY with CDN - resultsResults
Benefits of SPDY increased with for regions close to the PoP
LinkedIn network stack Overly simplified
LinkedIn network stack Pushing the CDN aside
Static content vs. base pages – round 2
Combining SPDY with CDNsDeploy SPDY stacks around the globe
Modern CDNs do pretty good job accelerating HTTP SPDY accelerates web content delivery further Serving static content through SPDY accelerates LinkedIn page In the long run, CDNs will support SPDY (HTTP/2.0). This will
make the web faster for everybody.
Bottom lineSPDY makes web faster; so do CDNs
Questions
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