From 04339ac16662c8233c33f84e3a65fda1b104928d Mon Sep 17 00:00:00 2001 From: mediocregopher Date: Sat, 19 Jan 2013 01:39:43 -0500 Subject: started post on active,once being bad --- erlang-tcp-socket-pull-pattern.md | 33 +++++++++++++++++++++++++++++++++ 1 file changed, 33 insertions(+) create mode 100644 erlang-tcp-socket-pull-pattern.md diff --git a/erlang-tcp-socket-pull-pattern.md b/erlang-tcp-socket-pull-pattern.md new file mode 100644 index 0000000..c17a799 --- /dev/null +++ b/erlang-tcp-socket-pull-pattern.md @@ -0,0 +1,33 @@ +# Erlang, tcp sockets, and active true + +If you don't know erlang then [you're missing out](http://learnyousomeerlang.com/content). +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](http://www.metabrew.com/article/a-million-user-comet-application-with-mochiweb-part-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](http://www.erlang.org/doc/man/inet.html#setopts-2) +flag. A socket can be set to one of: + +* `{active,false}` - All data must be obtained through [recv/2](http://www.erlang.org/doc/man/gen_tcp.html#recv-2) + 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](http://www.erlang.org/doc/man/gen_tcp.html#recv-2) + or be put in `{active,once}` or `{active,true}`. + +# Which to use? + + + +# Why not to use it + + -- cgit v1.2.3 From e5e7a5d52e2a81bcf5dfc188f10399115b894fc0 Mon Sep 17 00:00:00 2001 From: mediocregopher Date: Sat, 9 Mar 2013 14:23:39 -0500 Subject: fleshed out the rest of the erlang active once post --- erlang-tcp-socket-pull-pattern.md | 184 +++++++++++++++++++++++++++++++++++++- 1 file changed, 182 insertions(+), 2 deletions(-) diff --git a/erlang-tcp-socket-pull-pattern.md b/erlang-tcp-socket-pull-pattern.md index c17a799..d8a60d9 100644 --- a/erlang-tcp-socket-pull-pattern.md +++ b/erlang-tcp-socket-pull-pattern.md @@ -26,8 +26,188 @@ flag. A socket can be set to one of: # 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 it +# 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](http://www.erlang.org/doc/man/eprof.html) 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 -- cgit v1.2.3 From 9959c88cc4b23366cda16cff6e72298f579111e1 Mon Sep 17 00:00:00 2001 From: mediocregopher Date: Sat, 9 Mar 2013 14:34:05 -0500 Subject: added README as index for this thing --- README.md | 7 +++++++ 1 file changed, 7 insertions(+) create mode 100644 README.md diff --git a/README.md b/README.md new file mode 100644 index 0000000..e11fbfe --- /dev/null +++ b/README.md @@ -0,0 +1,7 @@ +This is my here blog. It's not much at the moment (one post? booyah!), but maybe it'll grow. + +Maybe not + +* [Erlang, tcp sockets, and active true](erlang-tcp-socket-pull-pattern.md) (originally posted March 9, 2013) + +That's all folks! -- cgit v1.2.3 From a4e2f98c269ca7bd090eed21aece8e74625ca612 Mon Sep 17 00:00:00 2001 From: mediocregopher Date: Sat, 9 Mar 2013 14:34:58 -0500 Subject: made references be a bullet list --- erlang-tcp-socket-pull-pattern.md | 6 +++--- 1 file changed, 3 insertions(+), 3 deletions(-) diff --git a/erlang-tcp-socket-pull-pattern.md b/erlang-tcp-socket-pull-pattern.md index d8a60d9..dca91e3 100644 --- a/erlang-tcp-socket-pull-pattern.md +++ b/erlang-tcp-socket-pull-pattern.md @@ -208,6 +208,6 @@ receiving a large amount of traffic. 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/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 -- cgit v1.2.3 From 6d80ce514e3b2ec096d713ab6e448caa25c22dbf Mon Sep 17 00:00:00 2001 From: Brian Picciano Date: Thu, 11 Jul 2013 21:27:58 -0400 Subject: go+ --- README.md | 1 + goplus.md | 59 +++++++++++++++++++++++++++++++++++++++++++++++++++++++++++ res/go+ | 27 +++++++++++++++++++++++++++ 3 files changed, 87 insertions(+) create mode 100644 goplus.md create mode 100755 res/go+ diff --git a/README.md b/README.md index e11fbfe..decf5fb 100644 --- a/README.md +++ b/README.md @@ -3,5 +3,6 @@ This is my here blog. It's not much at the moment (one post? booyah!), but maybe Maybe not * [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) That's all folks! diff --git a/goplus.md b/goplus.md new file mode 100644 index 0000000..c9b0191 --- /dev/null +++ b/goplus.md @@ -0,0 +1,59 @@ +# 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 $@ +``` diff --git a/res/go+ b/res/go+ new file mode 100755 index 0000000..835a72d --- /dev/null +++ b/res/go+ @@ -0,0 +1,27 @@ +#!/bin/sh + +SEARCHING_FOR=GOPROJROOT +ORIG_DIR=$(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 $@ -- cgit v1.2.3 From 35f1708c1f59050b46b8ba387e2906755bfa73d5 Mon Sep 17 00:00:00 2001 From: Brian Picciano Date: Tue, 8 Oct 2013 22:26:08 -0400 Subject: gq and reference-style-link everything --- erlang-tcp-socket-pull-pattern.md | 133 ++++++++++++++++++++++++-------------- goplus.md | 29 +++++---- 2 files changed, 102 insertions(+), 60 deletions(-) diff --git a/erlang-tcp-socket-pull-pattern.md b/erlang-tcp-socket-pull-pattern.md index dca91e3..419d005 100644 --- a/erlang-tcp-socket-pull-pattern.md +++ b/erlang-tcp-socket-pull-pattern.md @@ -1,46 +1,62 @@ # Erlang, tcp sockets, and active true -If you don't know erlang then [you're missing out](http://learnyousomeerlang.com/content). -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](http://www.metabrew.com/article/a-million-user-comet-application-with-mochiweb-part-1). +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](http://www.erlang.org/doc/man/inet.html#setopts-2) -flag. A socket can be set to one of: - -* `{active,false}` - All data must be obtained through [recv/2](http://www.erlang.org/doc/man/gen_tcp.html#recv-2) - 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](http://www.erlang.org/doc/man/gen_tcp.html#recv-2) - or be put in `{active,once}` or `{active,true}`. +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. +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: +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}]). +-define(TCP_OPTS, [ + binary, + {packet, raw}, + {nodelay,true}, + {active, false}, + {reuseaddr, true}, + {keepalive,true}, + {backlog,500} +]). %Start listening listen(Port) -> @@ -66,15 +82,16 @@ read_loop(Socket) -> 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: +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](http://www.erlang.org/doc/man/eprof.html) we can get an idea -of how our code performs, and where the hang-ups are: +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(). @@ -111,18 +128,30 @@ 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`. +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: +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}]). +-define(TCP_OPTS, [ + binary, + {packet, raw}, + {nodelay,true}, + {active, false}, + {reuseaddr, true}, + {keepalive,true}, + {backlog,500} +]). %Start listening listen(Port) -> @@ -194,20 +223,30 @@ 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. +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. +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. +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/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/goplus.md b/goplus.md index c9b0191..e6d9f85 100644 --- a/goplus.md +++ b/goplus.md @@ -1,16 +1,19 @@ # 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 `$GOPATH` and stops the search. Regardless of whether -or not `GOPROJROOT` was found go+ will passthrough all arguments to the actual go call. The +Compared to other languages go has some strange behavior regarding its project +root settings. If you import a library called `somelib`, go will look for a +`src/somelib` folder in all of the folders in the `$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 `$GOPATH` will only last the duration of the call. As an example, consider the following: @@ -23,8 +26,8 @@ As an example, consider the following: /hello.go ``` -If `hello.go` depends on `somelib`, as long as you run go+ from `/tmp/hello` or one of its children -your project will still compile +If `hello.go` depends on `somelib`, as long as you run go+ from `/tmp/hello` or +one of its children your project will still compile Here is the source code for go+: -- cgit v1.2.3 From 9624df51ec97b258da152d8807619c56104f7815 Mon Sep 17 00:00:00 2001 From: Brian Picciano Date: Tue, 8 Oct 2013 22:19:12 -0400 Subject: added in goat shoutout to go+ post --- goplus.md | 11 +++++++++++ 1 file changed, 11 insertions(+) diff --git a/goplus.md b/goplus.md index e6d9f85..58ab303 100644 --- a/goplus.md +++ b/goplus.md @@ -60,3 +60,14 @@ done cd "$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 -- cgit v1.2.3 From 1517dc3d0ad0c0fbcee2c11e4477fcf92a47f0d6 Mon Sep 17 00:00:00 2001 From: Brian Picciano Date: Tue, 8 Oct 2013 23:15:23 -0400 Subject: generations --- README.md | 1 + generations.md | 95 ++++++++++++++++++++++++++++++++++++++++++++++++++++++++++ 2 files changed, 96 insertions(+) create mode 100644 generations.md diff --git a/README.md b/README.md index decf5fb..4d685c9 100644 --- a/README.md +++ b/README.md @@ -4,5 +4,6 @@ Maybe not * [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) That's all folks! 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 -- cgit v1.2.3