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| -rw-r--r-- | README.md | 75 | ||||
| -rw-r--r-- | erlang-tcp-socket-pull-pattern.md | 252 | ||||
| -rw-r--r-- | generations.md | 95 | ||||
| -rw-r--r-- | goplus.md | 73 | ||||
| -rw-r--r-- | lagom-master.zip | bin | 216464 -> 0 bytes | |||
| -rw-r--r-- | lagom-master/.gitignore | 2 | ||||
| -rwxr-xr-x | res/go+ | 27 |
7 files changed, 453 insertions, 71 deletions
@@ -1,72 +1,9 @@ -# Lagom +This is my here blog. It's not much at the moment (one post? booyah!), but maybe it'll grow. -> #### *Lagom* is a Swedish word with no direct English equivalent, meaning "just the right amount" +Maybe not -Lagom, a [Jekyll][j] blog theme with just the right amount of style. +* [Erlang, tcp sockets, and active true](erlang-tcp-socket-pull-pattern.md) (originally posted March 9, 2013) +* [go+](goplus.md) (originally posted July 11, 2013) +* [Generations](generations.md) (originally posted October 8, 2013) -Extracted lovingly from [http://mdswanson.com][mds] for your enjoyment! - -* Responsive, based on [Skeleton][skeleton] -* [Font Awesome][font-awesome] for icons -* Open Sans from [Google web fonts][gfonts] -* Built-in Atom RSS feed - -## Action Shots - - - - -## Installation - -- Install Jekyll: `gem install jekyll` -- [Fork this repository][fork] -- Clone it: `git clone https://github.com/YOUR-USER/lagom` -- Run the jekyll server: `jekyll serve` - -You should have a server up and running locally at <http://localhost:4000>. - -## Customization - -Next you'll want to change a few things. Most of them can be changed directly in -[_config.yml][config]. That's where you can add your social links, change the accent -color, stuff like that. - -There's a few other places that you'll want to change, too: - -- [CNAME][cname]: If you're using this on GitHub Pages with a custom domain name, - you'll want to change this to be the domain you're going to use. All that should - be in here is a domain name on the first line and nothing else (like: `example.com`). -- [favicon.png][favicon]: This is the icon in your browser's address bar. You should - change it to whatever you'd like. -- [logo.png][logo]: A square-ish image that appears in the upper-left corner - -## Deployment - -You should deploy with [GitHub Pages][pages] - it's just easier. - -All you should have to do is rename your repository on GitHub to be -`username.github.io`. Since everything is on the `gh-pages` branch, you -should be able to see your new site at <http://username.github.io>. - -## Licensing - -[MIT](https://github.com/swanson/lagom/blob/master/LICENSE) with no -added caveats, so feel free to use this on your site without linking back to -me or using a disclaimer or anything silly like that. - -## Contact -I'd love to hear from you at [@_swanson][twitter]. Feel free to open issues if you -run into trouble or have suggestions. Pull Requests always welcome. - -[j]: http://jekyllrb.com/ -[mds]: http://mdswanson.com -[skeleton]: http://www.getskeleton.com/ -[font-awesome]: http://fortawesome.github.io/Font-Awesome/ -[gfonts]: http://www.google.com/fonts/specimen/Open+Sans -[fork]: https://github.com/swanson/lagom/fork -[config]: https://github.com/swanson/lagom/blob/master/_config.yml -[cname]: https://github.com/swanson/lagom/blob/master/CNAME -[favicon]: https://github.com/swanson/lagom/blob/master/favicon.png -[logo]: https://github.com/swanson/lagom/blob/master/logo.png -[pages]: http://pages.github.com -[twitter]: https://twitter.com/_swanson +That's all folks! diff --git a/erlang-tcp-socket-pull-pattern.md b/erlang-tcp-socket-pull-pattern.md new file mode 100644 index 0000000..419d005 --- /dev/null +++ b/erlang-tcp-socket-pull-pattern.md @@ -0,0 +1,252 @@ +# Erlang, tcp sockets, and active true + +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/generations.md b/generations.md new file mode 100644 index 0000000..d36b175 --- /dev/null +++ b/generations.md @@ -0,0 +1,95 @@ +# Generations + +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/goplus.md b/goplus.md new file mode 100644 index 0000000..58ab303 --- /dev/null +++ b/goplus.md @@ -0,0 +1,73 @@ +# Go and project root + +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 $@ +``` + +# UPDATE: Goat + +I'm leaving this post for posterity, but go+ has some serious flaws in it. For +one, it doesn't allow for specifying the version of a dependency you want to +use. To this end, I wrote [goat][0] which does all the things go+ does, plus +real dependency management, PLUS it is built in a way that if you've been +following go's best-practices for code organization you shouldn't have to change +any of your existing code AT ALL. It's cool, check it out. + +[0]: http://github.com/mediocregopher/goat diff --git a/lagom-master.zip b/lagom-master.zip Binary files differdeleted file mode 100644 index ef9cd79..0000000 --- a/lagom-master.zip +++ /dev/null diff --git a/lagom-master/.gitignore b/lagom-master/.gitignore deleted file mode 100644 index f11e635..0000000 --- a/lagom-master/.gitignore +++ /dev/null @@ -1,2 +0,0 @@ -_site/ -.DS_Store
\ No newline at end of file @@ -0,0 +1,27 @@ +#!/bin/sh + +SEARCHING_FOR=GOPROJROOT +ORIG_DIR=$(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 $@ |