fixed posts, got rid of sample posts

5 files changed, 435 insertions, 84 deletions

diff --git a/_posts/2013-08-12-another-sample.md b/_posts/2013-08-12-another-sample.md
deleted file mode 100644
index 2a0de20..0000000
--- a/_posts/2013-08-12-another-sample.md
+++ /dev/null
@@ -1,42 +0,0 @@
----
-layout: post
-title: Another sample
-categories:
-- blog
----
-
-Tattooed roof party *vinyl* freegan single-origin coffee wayfarers tousled, umami yr 
-meggings hella selvage. Butcher bespoke seitan, cornhole umami gentrify put a bird 
-on it occupy trust fund. Umami whatever kitsch, locavore fingerstache Tumblr pork belly
-[keffiyeh](#). Chia Echo Park Pitchfork, Blue Bottle [hashtag](#) stumptown skateboard selvage 
-mixtape. Echo Park retro butcher banjo cardigan, seitan flannel Brooklyn paleo fixie 
-Truffaut. Forage mustache Thundercats next level disrupt. Bicycle rights forage tattooed
-chia, **wayfarers** swag raw denim hashtag biodiesel occupy gastropub!
-
----
-
-# It's all in the game.
-## You come at the king, you best not miss.
-### Be subtle with it, man. You know what subtle means?
-
-VHS post-ironic cred **bespoke** banjo. Yr wayfarers literally gentrify, flexitarian fap 
-dreamcatcher plaid cornhole Intelligentsia paleo. Beard try-hard direct trade, shabby chic 
-Helvetica `look ma, I can code`. Lo-fi American Apparel tattooed [Vice](#) tofu, yr vinyl. 
-Williamsburg butcher hella mumblecore fixie mlkshk, cliche wolf keytar mixtape kitsch banh mi 
-salvia. High Life Odd Future *chambray* kale chips hoodie, cray pop-up. Helvetica narwhal 
-iPhone try-hard jean shorts.
-
-> This is a quote from someone famous about productivity
-
-
-Syntax highlighting with Solarized theme.
-
-{% highlight ruby %}
-class User < ActiveRecord::Base
-  attr_accessible :email, :name
-
-  ... tons of other crap ...
-
-end
-
-{% endhighlight %}
diff --git a/_posts/2013-08-20-sample-post.md b/_posts/2013-08-20-sample-post.md
deleted file mode 100644
index ea372fa..0000000
--- a/_posts/2013-08-20-sample-post.md
+++ /dev/null
@@ -1,42 +0,0 @@
----
-layout: post
-title: Sample post
-categories:
-- blog
----
-
-Tattooed roof party *vinyl* freegan single-origin coffee wayfarers tousled, umami yr 
-meggings hella selvage. Butcher bespoke seitan, cornhole umami gentrify put a bird 
-on it occupy trust fund. Umami whatever kitsch, locavore fingerstache Tumblr pork belly
-[keffiyeh](#). Chia Echo Park Pitchfork, Blue Bottle [hashtag](#) stumptown skateboard selvage 
-mixtape. Echo Park retro butcher banjo cardigan, seitan flannel Brooklyn paleo fixie 
-Truffaut. Forage mustache Thundercats next level disrupt. Bicycle rights forage tattooed
-chia, **wayfarers** swag raw denim hashtag biodiesel occupy gastropub!
-
----
-
-# It's all in the game.
-## You come at the king, you best not miss.
-### Be subtle with it, man. You know what subtle means?
-
-VHS post-ironic cred **bespoke** banjo. Yr wayfarers literally gentrify, flexitarian fap 
-dreamcatcher plaid cornhole Intelligentsia paleo. Beard try-hard direct trade, shabby chic 
-Helvetica `look ma, I can code`. Lo-fi American Apparel tattooed [Vice](#) tofu, yr vinyl. 
-Williamsburg butcher hella mumblecore fixie mlkshk, cliche wolf keytar mixtape kitsch banh mi 
-salvia. High Life Odd Future *chambray* kale chips hoodie, cray pop-up. Helvetica narwhal 
-iPhone try-hard jean shorts.
-
-> This is a quote from someone famous about productivity
-
-
-Syntax highlighting with Solarized theme.
-
-{% highlight ruby %}
-class User < ActiveRecord::Base
-  attr_accessible :email, :name
-
-  ... tons of other crap ...
-
-end
-
-{% endhighlight %}
diff --git a/_posts/2013-10-8-generations.md b/_posts/2013-10-8-generations.md
new file mode 100644
index 0000000..904f625
--- /dev/null
+++ b/_posts/2013-10-8-generations.md
@@ -0,0 +1,100 @@
+---
+layout: post
+title: Generations
+categories:
+- crypticio
+---
+
+A simple file distribution strategy for very large scale, high-availability
+file-services.
+
+# The problem
+
+Working at a shop where we have millions of different files, any of which could
+be arbitrarily chosen to serve to a file at any given time. These files are
+uploaded by users of the app and retrieved by others.
+
+Scaling such a system is no easy task. The chosen solution involves shuffling
+files around on a nearly constant basis, making sure that files which are more
+"popular" are on fast drives, while at the same time making sure that no drives
+are at capicty and at the same time that all files, even newly uploaded ones,
+are stored redundantly.
+
+The problem with this solution is one of coordination. At any given moment the
+app needs to be able to "find" a file so it can give the client a link to
+download the file from one of the servers that it's on. Full-filling this simple
+requirement means that all datastores/caches where information about where a
+file lives need to be up-to-date at all times, and even then there are
+race-conditions and network failures to contend with, while at all times the
+requirements of the app evolve and change.
+
+# A simpler solution
+
+Let's say you want all files which get uploaded to be replicated in triplicate
+in some capacity. You buy three identical hard-disks, and put each on a separate
+server.  As files get uploaded by clients, each file gets put on each drive
+immediately. When the drives are filled (which should be at around the same
+time), you stop uploading to them.
+
+That was generation 0.
+
+You buy three more drives, and start putting all files on them instead. This is
+going to be generation 1. Repeat until you run out of money.
+
+That's it.
+
+## That's it?
+
+It seems simple and obvious, and maybe it's the standard thing which is done,
+but as far as I can tell no-one has written about it (though I'm probably not
+searching for the right thing, let me know if this is the case!).
+
+## Advantages
+
+* It's so simple to implement, you could probably do it in a day if you're
+starting a project from scratch
+
+* By definition of the scheme all files are replicated in multiple places.
+
+* Minimal information about where a file "is" needs to be stored. When a file is
+uploaded all that's needed is to know what generation it is in, and then what
+nodes/drives are in that generation.
+
+* Drives don't need to "know" about each other. What I mean by this is that
+whatever is running as the receive point for file-uploads on each drive doesn't
+have to coordinate with its siblings running on the other drives in the
+generation. In fact it doesn't need to coordinate with anyone. You could
+literally rsync files onto your drives if you wanted to. I would recommend using
+[marlin][0] though :)
+
+* Scaling is easy. When you run out of space you can simply start a new
+generation. If you don't like playing that close to the chest there's nothing to
+say you can't have two generations active at the same time.
+
+* Upgrading is easy. As long as a generation is not marked-for-upload, you can
+easily copy all files in the generation into a new set of bigger, badder drives,
+add those drives into the generation in your code, remove the old ones, then
+mark the generation as uploadable again.
+
+* Distribution is easy. You just copy a generation's files onto a new drive in
+Europe or wherever you're getting an uptick in traffic from and you're good to
+go.
+
+* Management is easy. It's trivial to find out how many times a file has been
+replicated, or how many countries it's in, or what hardware it's being served
+from (given you have easy access to information about specific drives).
+
+## Caveats
+
+The big caveat here is that this is just an idea. It has NOT been tested in
+production. But we have enough faith in it that we're going to give it a shot at
+cryptic.io. I'll keep this page updated.
+
+The second caveat is that this scheme does not inherently support caching. If a
+file suddenly becomes super popular the world over your hard-disks might not be
+able to keep up, and it's probably not feasible to have an FIO drive in *every*
+generation. I think that [groupcache][1] may be the answer to this problem,
+assuming your files are reasonably small, but again I haven't tested it yet.
+
+[0]: https://github.com/cryptic-io/marlin
+[1]: https://github.com/golang/groupcache
diff --git a/_posts/2013-4-9-erlang-tcp-socket-pull-pattern.md b/_posts/2013-4-9-erlang-tcp-socket-pull-pattern.md
new file mode 100644
index 0000000..23d1736
--- /dev/null
+++ b/_posts/2013-4-9-erlang-tcp-socket-pull-pattern.md
@@ -0,0 +1,257 @@
+---
+layout: post
+title: "Erlang, tcp sockets, and active true"
+categories:
+- erlang
+---
+
+If you don't know erlang then [you're missing out][0].  If you do know erlang,
+you've probably at some point done something with tcp sockets. Erlang's highly
+concurrent model of execution lends itself well to server programs where a high
+number of active connections is desired. Each thread can autonomously handle its
+single client, greatly simplifying the logic of the whole application while
+still retaining [great performance characteristics][1].
+
+# Background
+
+For an erlang thread which owns a single socket there are three different ways
+to receive data off of that socket. These all revolve around the `active`
+[setopts][2] flag. A socket can be set to one of:
+
+* `{active,false}` - All data must be obtained through [recv/2][3] calls. This
+                     amounts to syncronous socket reading.
+
+* `{active,true}`  - All data on the socket gets sent to the controlling thread
+                     as a normal erlang message. It is the thread's
+                     responsibility to keep up with the buffered data in the
+                     message queue. This amounts to asyncronous socket reading.
+
+* `{active,once}`  - When set the socket is placed in `{active,true}` for a
+                     single packet. That is, once set the thread can expect a
+                     single message to be sent to when data comes in. To receive
+                     any more data off of the socket the socket must either be
+                     read from using [recv/2][3] or be put in `{active,once}` or
+                     `{active,true}`.
+
+# Which to use?
+
+Many (most?) tutorials advocate using `{active,once}` in your application
+\[0]\[1]\[2]. This has to do with usability and security. When in `{active,true}`
+it's possible for a client to flood the connection faster than the receiving
+process will process those messages, potentially eating up a lot of memory in
+the VM. However, if you want to be able to receive both tcp data messages as
+well as other messages from other erlang processes at the same time you can't
+use `{active,false}`.  So `{active,once}` is generally preferred because it
+deals with both of these problems quite well.
+
+# Why not to use `{active,once}`
+
+Here's what your classic `{active,once}` enabled tcp socket implementation will
+probably look like:
+
+```erlang
+-module(tcp_test).
+-compile(export_all).
+
+-define(TCP_OPTS, [
+    binary,
+    {packet, raw},
+    {nodelay,true},
+    {active, false},
+    {reuseaddr, true},
+    {keepalive,true},
+    {backlog,500}
+]).
+
+%Start listening
+listen(Port) ->
+    {ok, L} = gen_tcp:listen(Port, ?TCP_OPTS),
+    ?MODULE:accept(L).
+
+%Accept a connection
+accept(L) ->
+    {ok, Socket} = gen_tcp:accept(L),
+    ?MODULE:read_loop(Socket),
+    io:fwrite("Done reading, connection was closed\n"),
+    ?MODULE:accept(L).
+
+%Read everything it sends us
+read_loop(Socket) ->
+    inet:setopts(Socket, [{active, once}]),
+    receive
+    {tcp, _, _} ->
+        do_stuff_here,
+        ?MODULE:read_loop(Socket);
+    {tcp_closed, _}-> donezo;
+    {tcp_error, _, _} -> donezo
+    end.
+```
+
+This code isn't actually usable for a production system; it doesn't even spawn a
+new process for the new socket. But that's not the point I'm making. If I run it
+with `tcp_test:listen(8000)`, and in other window do:
+
+```bash
+while [ 1 ]; do echo "aloha"; done | nc localhost 8000
+```
+
+We'll be flooding the the server with data pretty well. Using [eprof][4] we can
+get an idea of how our code performs, and where the hang-ups are:
+
+```erlang
+1> eprof:start().
+{ok,<0.34.0>}
+
+2> P = spawn(tcp_test,listen,[8000]).
+<0.36.0>
+
+3> eprof:start_profiling([P]).
+profiling
+
+4> running_the_while_loop.
+running_the_while_loop
+
+5> eprof:stop_profiling().
+profiling_stopped
+
+6> eprof:analyze(procs,[{sort,time}]).
+
+****** Process <0.36.0>    -- 100.00 % of profiled time *** 
+FUNCTION                           CALLS      %      TIME  [uS / CALLS]
+--------                           -----    ---      ----  [----------]
+prim_inet:type_value_2/2               6   0.00         0  [      0.00]
+
+....snip....
+
+prim_inet:enc_opts/2                   6   0.00         8  [      1.33]
+prim_inet:setopts/2             12303599   1.85   1466319  [      0.12]
+tcp_test:read_loop/1            12303598   2.22   1761775  [      0.14]
+prim_inet:encode_opt_val/1      12303599   3.50   2769285  [      0.23]
+prim_inet:ctl_cmd/3             12303600   4.29   3399333  [      0.28]
+prim_inet:enc_opt_val/2         24607203   5.28   4184818  [      0.17]
+inet:setopts/2                  12303598   5.72   4533863  [      0.37]
+erlang:port_control/3           12303600  77.13  61085040  [      4.96]
+```
+
+eprof shows us where our process is spending the majority of its time. The `%`
+column indicates percentage of time the process spent during profiling inside
+any function. We can pretty clearly see that the vast majority of time was spent
+inside `erlang:port_control/3`, the BIF that `inet:setopts/2` uses to switch the
+socket to `{active,once}` mode. Amongst the calls which were called on every
+loop, it takes up by far the most amount of time. In addition all of those other
+calls are also related to `inet:setopts/2`.
+
+I'm gonna rewrite our little listen server to use `{active,true}`, and we'll do
+it all again:
+
+```erlang
+-module(tcp_test).
+-compile(export_all).
+
+-define(TCP_OPTS, [
+    binary,
+    {packet, raw},
+    {nodelay,true},
+    {active, false},
+    {reuseaddr, true},
+    {keepalive,true},
+    {backlog,500}
+]).
+
+%Start listening
+listen(Port) ->
+    {ok, L} = gen_tcp:listen(Port, ?TCP_OPTS),
+    ?MODULE:accept(L).
+
+%Accept a connection
+accept(L) ->
+    {ok, Socket} = gen_tcp:accept(L),
+    inet:setopts(Socket, [{active, true}]), %Well this is new
+    ?MODULE:read_loop(Socket),
+    io:fwrite("Done reading, connection was closed\n"),
+    ?MODULE:accept(L).
+
+%Read everything it sends us
+read_loop(Socket) ->
+    %inet:setopts(Socket, [{active, once}]),
+    receive
+    {tcp, _, _} ->
+        do_stuff_here,
+        ?MODULE:read_loop(Socket);
+    {tcp_closed, _}-> donezo;
+    {tcp_error, _, _} -> donezo
+    end.
+```
+
+And the profiling results:
+
+```erlang
+1> eprof:start().
+{ok,<0.34.0>}
+
+2>  P = spawn(tcp_test,listen,[8000]).
+<0.36.0>
+
+3> eprof:start_profiling([P]).
+profiling
+
+4>  running_the_while_loop.
+running_the_while_loop
+
+5> eprof:stop_profiling().
+profiling_stopped
+
+6> eprof:analyze(procs,[{sort,time}]).
+
+****** Process <0.36.0>    -- 100.00 % of profiled time *** 
+FUNCTION                           CALLS       %      TIME  [uS / CALLS]
+--------                           -----     ---      ----  [----------]
+prim_inet:enc_value_1/3                7    0.00         1  [      0.14]
+prim_inet:decode_opt_val/1             1    0.00         1  [      1.00]
+inet:setopts/2                         1    0.00         2  [      2.00]
+prim_inet:setopts/2                    2    0.00         2  [      1.00]
+prim_inet:enum_name/2                  1    0.00         2  [      2.00]
+erlang:port_set_data/2                 1    0.00         2  [      2.00]
+inet_db:register_socket/2              1    0.00         3  [      3.00]
+prim_inet:type_value_1/3               7    0.00         3  [      0.43]
+
+.... snip ....
+
+prim_inet:type_opt_1/1                19    0.00         7  [      0.37]
+prim_inet:enc_value/3                  7    0.00         7  [      1.00]
+prim_inet:enum_val/2                   6    0.00         7  [      1.17]
+prim_inet:dec_opt_val/1                7    0.00         7  [      1.00]
+prim_inet:dec_value/2                  6    0.00        10  [      1.67]
+prim_inet:enc_opt/1                   13    0.00        12  [      0.92]
+prim_inet:type_opt/2                  19    0.00        33  [      1.74]
+erlang:port_control/3                  3    0.00        59  [     19.67]
+tcp_test:read_loop/1            20716370  100.00  12187488  [      0.59]
+```
+
+This time our process spent almost no time at all (according to eprof, 0%)
+fiddling with the socket opts.  Instead it spent all of its time in the
+read_loop doing the work we actually want to be doing.
+
+# So what does this mean?
+
+I'm by no means advocating never using `{active,once}`. The security concern is
+still a completely valid concern and one that `{active,once}` mitigates quite
+well. I'm simply pointing out that this mitigation has some fairly serious
+performance implications which have the potential to bite you if you're not
+careful, especially in cases where a socket is going to be receiving a large
+amount of traffic.
+
+# Meta
+
+These tests were done using R15B03, but I've done similar ones in R14 and found
+similar results. I have not tested R16.
+
+* \[0] http://learnyousomeerlang.com/buckets-of-sockets
+* \[1] http://www.erlang.org/doc/man/gen_tcp.html#examples
+* \[2] http://erlycoder.com/25/erlang-tcp-server-tcp-client-sockets-with-gen_tcp
+
+[0]: http://learnyousomeerlang.com/content
+[1]: http://www.metabrew.com/article/a-million-user-comet-application-with-mochiweb-part-1
+[2]: http://www.erlang.org/doc/man/inet.html#setopts-2
+[3]: http://www.erlang.org/doc/man/gen_tcp.html#recv-2
+[4]: http://www.erlang.org/doc/man/eprof.html
diff --git a/_posts/2013-7-11-goplus.md b/_posts/2013-7-11-goplus.md
new file mode 100644
index 0000000..0b76add
--- /dev/null
+++ b/_posts/2013-7-11-goplus.md
@@ -0,0 +1,78 @@
+---
+layout: post
+title: Go+
+categories:
+- go
+---
+
+Compared to other languages go has some strange behavior regarding its project
+root settings. If you import a library called `somelib`, go will look for a
+`src/somelib` folder in all of the folders in the `$GOPATH` environment
+variable. This works nicely for globally installed packages, but it makes
+encapsulating a project with a specific version, or modified version, rather
+tedious. Whenever you go to work on this project you'll have to add its path to
+your `$GOPATH`, or add the path permanently, which could break other projects
+which may use a different version of `somelib`.
+
+My solution is in the form of a simple script I'm calling go+. go+ will search
+in currrent directory and all of its parents for a file called `GOPROJROOT`. If
+it finds that file in a directory, it prepends that directory's absolute path to
+your `$GOPATH` and stops the search. Regardless of whether or not `GOPROJROOT`
+was found go+ will passthrough all arguments to the actual go call. The
+modification to `$GOPATH` will only last the duration of the call.
+
+As an example, consider the following:
+```
+/tmp
+    /hello
+        GOPROJROOT
+        /src
+            /somelib/somelib.go
+            /hello.go
+```
+
+If `hello.go` depends on `somelib`, as long as you run go+ from `/tmp/hello` or
+one of its children your project will still compile
+
+Here is the source code for go+:
+
+```bash
+#!/bin/sh
+
+SEARCHING_FOR=GOPROJROOT
+ORIG_DIR=$(pwd)
+
+STOPSEARCH=0
+SEARCH_DIR=$ORIG_DIR
+while [ $STOPSEARCH = 0 ]; do
+
+    RES=$( find $SEARCH_DIR -maxdepth 1 -type f -name $SEARCHING_FOR | \
+           grep -P "$SEARCHING_FOR$" | \
+           head -n1 )
+
+    if [ "$RES" = "" ]; then
+        if [ "$SEARCH_DIR" = "/" ]; then
+            STOPSEARCH=1
+        fi
+        cd ..
+        SEARCH_DIR=$(pwd)
+    else
+        export GOPATH=$SEARCH_DIR:$GOPATH
+        STOPSEARCH=1
+    fi
+done
+
+cd "$ORIG_DIR"
+exec go $@
+```
+
+# UPDATE: Goat
+
+I'm leaving this post for posterity, but go+ has some serious flaws in it. For
+one, it doesn't allow for specifying the version of a dependency you want to
+use. To this end, I wrote [goat][0] which does all the things go+ does, plus
+real dependency management, PLUS it is built in a way that if you've been
+following go's best-practices for code organization you shouldn't have to change
+any of your existing code AT ALL. It's cool, check it out.
+
+[0]: http://github.com/mediocregopher/goat