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doc: PHILOSOPHY: formatting fixes

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1 parent 77a951c commit c20077db941cc969fb3721c7527d37a99367f220 Eric Wong committed May 8, 2011
Showing with 49 additions and 49 deletions.
  1. +49 −49 PHILOSOPHY
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@@ -1,32 +1,32 @@
-= The Philosophy Behind Unicorn
+= The Philosophy Behind unicorn
-Being a server that only runs on Unix-like platforms, Unicorn is
+Being a server that only runs on Unix-like platforms, unicorn is
strongly tied to the Unix philosophy of doing one thing and (hopefully)
-doing it well. Despite using HTTP, Unicorn is strictly a _backend_
+doing it well. Despite using HTTP, unicorn is strictly a _backend_
application server for running Rack-based Ruby applications.
== Avoid Complexity
-Instead of attempting to be efficient at serving slow clients, Unicorn
+Instead of attempting to be efficient at serving slow clients, unicorn
relies on a buffering reverse proxy to efficiently deal with slow
clients.
-Unicorn uses an old-fashioned preforking worker model with blocking I/O.
+unicorn uses an old-fashioned preforking worker model with blocking I/O.
Our processing model is the antithesis of more modern (and theoretically
more efficient) server processing models using threads or non-blocking
I/O with events.
=== Threads and Events Are Hard
...to many developers. Reasons for this is beyond the scope of this
-document. Unicorn avoids concurrency within each worker process so you
+document. unicorn avoids concurrency within each worker process so you
have fewer things to worry about when developing your application. Of
-course Unicorn can use multiple worker processes to utilize multiple
+course unicorn can use multiple worker processes to utilize multiple
CPUs or spindles. Applications can still use threads internally, however.
== Slow Clients Are Problematic
-Most benchmarks we've seen don't tell you this, and Unicorn doesn't
+Most benchmarks we've seen don't tell you this, and unicorn doesn't
care about slow clients... but <i>you</i> should.
A "slow client" can be any client outside of your datacenter. Network
@@ -37,71 +37,71 @@ Persistent connections were introduced in HTTP/1.1 reduce latency from
connection establishment and TCP slow start. They also waste server
resources when clients are idle.
-Persistent connections mean one of the Unicorn worker processes
+Persistent connections mean one of the unicorn worker processes
(depending on your application, it can be very memory hungry) would
spend a significant amount of its time idle keeping the connection alive
<i>and not doing anything else</i>. Being single-threaded and using
blocking I/O, a worker cannot serve other clients while keeping a
-connection alive. Thus Unicorn does not implement persistent
+connection alive. Thus unicorn does not implement persistent
connections.
If your application responses are larger than the socket buffer or if
you're handling large requests (uploads), worker processes will also be
bottlenecked by the speed of the *client* connection. You should
-not allow Unicorn to serve clients outside of your local network.
+not allow unicorn to serve clients outside of your local network.
== Application Concurrency != Network Concurrency
Performance is asymmetric across the different subsystems of the machine
and parts of the network. CPUs and main memory can process gigabytes of
data in a second; clients on the Internet are usually only capable of a
-tiny fraction of that. Unicorn deployments should avoid dealing with
+tiny fraction of that. unicorn deployments should avoid dealing with
slow clients directly and instead rely on a reverse proxy to shield it
from the effects of slow I/O.
== Improved Performance Through Reverse Proxying
-By acting as a buffer to shield Unicorn from slow I/O, a reverse proxy
+By acting as a buffer to shield unicorn from slow I/O, a reverse proxy
will inevitably incur overhead in the form of extra data copies.
However, as I/O within a local network is fast (and faster still
with local sockets), this overhead is neglible for the vast majority
of HTTP requests and responses.
-The ideal reverse proxy complements the weaknesses of Unicorn.
-A reverse proxy for Unicorn should meet the following requirements:
-
- 1. It should fully buffer all HTTP requests (and large responses).
- Each request should be "corked" in the reverse proxy and sent
- as fast as possible to the backend Unicorn processes. This is
- the most important feature to look for when choosing a
- reverse proxy for Unicorn.
-
- 2. It should spend minimal time in userspace. Network (and disk) I/O
- are system-level tasks and usually managed by the kernel.
- This may change if userspace TCP stacks become more popular in the
- future; but the reverse proxy should not waste time with
- application-level logic. These concerns should be separated
-
- 3. It should avoid context switches and CPU scheduling overhead.
- In many (most?) cases, network devices and their interrupts are
- only be handled by one CPU at a time. It should avoid contention
- within the system by serializing all network I/O into one (or few)
- userspace procceses. Network I/O is not a CPU-intensive task and
- it is not helpful to use multiple CPU cores (at least not for GigE).
-
- 4. It should efficiently manage persistent connections (and
- pipelining) to slow clients. If you care to serve slow clients
- outside your network, then these features of HTTP/1.1 will help.
-
- 5. It should (optionally) serve static files. If you have static
- files on your site (especially large ones), they are far more
- efficiently served with as few data copies as possible (e.g. with
- sendfile() to completely avoid copying the data to userspace).
+The ideal reverse proxy complements the weaknesses of unicorn.
+A reverse proxy for unicorn should meet the following requirements:
+
+1. It should fully buffer all HTTP requests (and large responses).
+ Each request should be "corked" in the reverse proxy and sent
+ as fast as possible to the backend unicorn processes. This is
+ the most important feature to look for when choosing a
+ reverse proxy for unicorn.
+
+2. It should spend minimal time in userspace. Network (and disk) I/O
+ are system-level tasks and usually managed by the kernel.
+ This may change if userspace TCP stacks become more popular in the
+ future; but the reverse proxy should not waste time with
+ application-level logic. These concerns should be separated
+
+3. It should avoid context switches and CPU scheduling overhead.
+ In many (most?) cases, network devices and their interrupts are
+ only be handled by one CPU at a time. It should avoid contention
+ within the system by serializing all network I/O into one (or few)
+ userspace procceses. Network I/O is not a CPU-intensive task and
+ it is not helpful to use multiple CPU cores (at least not for GigE).
+
+4. It should efficiently manage persistent connections (and
+ pipelining) to slow clients. If you care to serve slow clients
+ outside your network, then these features of HTTP/1.1 will help.
+
+5. It should (optionally) serve static files. If you have static
+ files on your site (especially large ones), they are far more
+ efficiently served with as few data copies as possible (e.g. with
+ sendfile() to completely avoid copying the data to userspace).
nginx is the only (Free) solution we know of that meets the above
requirements.
-Indeed, the folks behind Unicorn have deployed nginx as a reverse-proxy not
+Indeed, the folks behind unicorn have deployed nginx as a reverse-proxy not
only for Ruby applications, but also for production applications running
Apache/mod_perl, Apache/mod_php and Apache Tomcat. In every single
case, performance improved because application servers were able to use
@@ -129,17 +129,17 @@ that is not the Unix way.
== Just Worse in Some Cases
-Unicorn is not suited for all applications. Unicorn is optimized for
+unicorn is not suited for all applications. unicorn is optimized for
applications that are CPU/memory/disk intensive and spend little time
waiting on external resources (e.g. a database server or external API).
-Unicorn is highly inefficient for Comet/reverse-HTTP/push applications
+unicorn is highly inefficient for Comet/reverse-HTTP/push applications
where the HTTP connection spends a large amount of time idle.
Nevertheless, the ease of troubleshooting, debugging, and management of
-Unicorn may still outweigh the drawbacks for these applications.
+unicorn may still outweigh the drawbacks for these applications.
The {Rainbows!}[http://rainbows.rubyforge.org/] aims to fill the gap for
-odd corner cases where the nginx + Unicorn combination is not enough.
+odd corner cases where the nginx + unicorn combination is not enough.
While Rainbows! management/administration is largely identical to
-Unicorn, Rainbows! is far more ambitious and has seen little real-world
+unicorn, Rainbows! is far more ambitious and has seen little real-world
usage.

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