Recon

Module recon

Recon, as a module, provides access to the high-level functionality contained in the Recon application.

Authors: Fred Hebert (mononcqc@ferd.ca) [web site: http://ferd.ca/].

Description

Recon, as a module, provides access to the high-level functionality contained in the Recon application.

It has functions in five main categories:

1. State information
Process information is everything that has to do with the general state of the node. Functions such as info/1 and info/3 are wrappers to provide more details than erlang:process_info/1, while providing it in a production-safe manner. They have equivalents to erlang:process_info/2 in the functions info/2 and info/4, respectively.
proc_count/2 and proc_window/3 are to be used when you require information about processes in a larger sense: biggest consumers of given process information (say memory or reductions), either absolutely or over a sliding time window, respectively.
bin_leak/1 is a function that can be used to try and see if your Erlang node is leaking refc binaries. See the function itself for more details.
Functions to access node statistics, in a manner somewhat similar to what vmstats provides as a library. There are 3 of them: node_stats_print/2, which displays them, node_stats_list/2, which returns them in a list, and node_stats/4, which provides a fold-like interface for stats gathering. For CPU usage specifically, see scheduler_usage/1.
2. OTP tools
This category provides tools to interact with pieces of OTP more easily. At this point, the only function included is get_state/1, which works as a wrapper around get_state/2, which works as a wrapper around sys:get_state/1 in R16B01, and provides the required functionality for older versions of Erlang.
3. Code Handling
Specific functions are in recon for the sole purpose of interacting with source and compiled code. remote_load/1 and remote_load/2 will allow to take a local module, and load it remotely (in a diskless manner) on another Erlang node you're connected to.
source/1 allows to print the source of a loaded module, in case it's not available in the currently running node.
4. Ports and Sockets
To make it simpler to debug some network-related issues, recon contains functions to deal with Erlang ports (raw, file handles, or inet). Functions tcp/0, udp/0, sctp/0, files/0, and port_types/0 will list all the Erlang ports of a given type. The latter function prints counts of all individual types.
Port state information can be useful to figure out why certain parts of the system misbehave. Functions such as port_info/1 and port_info/2 are wrappers to provide more similar or more details than erlang:port_info/1-2, and, for inet ports, statistics and options for each socket.
Finally, the functions inet_count/2 and inet_window/3 provide the absolute or sliding window functionality of proc_count/2 and proc_count/3 to inet ports and connections currently on the node.
5. RPC
These are wrappers to make RPC work simpler with clusters of Erlang nodes. Default RPC mechanisms (from the rpc module) make it somewhat painful to call shell-defined funs over node boundaries. The functions rpc/1, rpc/2, and rpc/3 will do it with a simpler interface.
Additionally, when you're running diagnostic code on remote nodes and want to know which node evaluated what result, using named_rpc/1, named_rpc/2, and named_rpc/3 will wrap the results in a tuple that tells you which node it's coming from, making it easier to identify bad nodes.

Data Types

inet_attrs()

inet_attrs() = {port(), Attr::term(), [{atom(), term()}]}

info_key()

info_key() = info_meta_key() | info_signals_key() | info_location_key() | info_memory_key() | info_work_key()

info_location_key()

info_location_key() = initial_call | current_stacktrace

info_memory_key()

info_memory_key() = memory | message_queue_len | heap_size | total_heap_size | garbage_collection

info_meta_key()

info_meta_key() = registered_name | dictionary | group_leader | status

info_signals_key()

info_signals_key() = links | monitors | monitored_by | trap_exit

info_type()

info_type() = meta | signals | location | memory_used | work

info_work_key()

info_work_key() = reductions

pid_term()

pid_term() = pid() | atom() | string() | {global, term()} | {via, module(), term()} | {non_neg_integer(), non_neg_integer(), non_neg_integer()}

port_info_io_key()

port_info_io_key() = input | output

port_info_key()

port_info_key() = port_info_meta_key() | port_info_signals_key() | port_info_io_key() | port_info_memory_key() | port_info_specific_key()

port_info_memory_key()

port_info_memory_key() = memory | queue_size

port_info_meta_key()

port_info_meta_key() = registered_name | id | name | os_pid

port_info_signals_key()

port_info_signals_key() = connected | links | monitors

port_info_specific_key()

port_info_specific_key() = atom()

port_info_type()

port_info_type() = meta | signals | io | memory_used | specific

port_term()

port_term() = port() | string() | atom() | pos_integer()

proc_attrs()

proc_attrs() = {pid(), Attr::term(), [Name::atom() | {current_function, mfa()} | {initial_call, mfa()}, ...]}

Function Index

bin_leak/1Refc binaries can be leaking when barely-busy processes route them around and do little else, or when extremely busy processes reach a stable amount of memory allocated and do the vast majority of their work with refc binaries.
files/0returns a list of all file handles open on the node.
get_state/1Shorthand call to recon:get_state(PidTerm, 5000)
get_state/2Fetch the internal state of an OTP process.
inet_count/2Fetches a given attribute from all inet ports (TCP, UDP, SCTP) and returns the biggest Num consumers.
inet_window/3Fetches a given attribute from all inet ports (TCP, UDP, SCTP) and returns the biggest entries, over a sliding time window.
info/1Allows to be similar to erlang:process_info/1, but excludes fields such as the mailbox, which have a tendency to grow and be unsafe when called in production systems.
info/2Allows to be similar to erlang:process_info/2, but allows to sort fields by safe categories and pre-selections, avoiding items such as the mailbox, which may have a tendency to grow and be unsafe when called in production systems.
info/3Equivalent to info(<A.B.C>) where A, B, and C are integers part of a pid.
info/4Equivalent to info(<A.B.C>, Key) where A, B, and C are integers part of a pid.
named_rpc/1Shorthand for named_rpc([node()|nodes()], Fun).
named_rpc/2Shorthand for named_rpc(Nodes, Fun, infinity).
named_rpc/3Runs an arbitrary fun (of arity 0) over one or more nodes, and returns the name of the node that computed a given result along with it, in a tuple.
node_stats/4Gathers statistics N time, waiting Interval milliseconds between each run, and accumulates results using a folding function FoldFun.
node_stats_list/2Shorthand for node_stats(N, Interval, fun(X,Acc) -> [X|Acc] end, []) with the results reversed to be in the right temporal order.
node_stats_print/2Shorthand for node_stats(N, Interval, fun(X,_) -> io:format("~p~n",[X]) end, nostate).
port_info/1Allows to be similar to erlang:port_info/1, but allows more flexible port usage: usual ports, ports that were registered locally (an atom), ports represented as strings ("#Port<0.2013>"), or through an index lookup (2013, for the same result as "#Port<0.2013>").
port_info/2Allows to be similar to erlang:port_info/2, but allows more flexible port usage: usual ports, ports that were registered locally (an atom), ports represented as strings ("#Port<0.2013>"), or through an index lookup (2013, for the same result as "#Port<0.2013>").
port_types/0Shows a list of all different ports on the node with their respective types.
proc_count/2Fetches a given attribute from all processes and returns the biggest Num consumers.
proc_window/3Fetches a given attribute from all processes and returns the biggest entries, over a sliding time window.
remote_load/1Equivalent to remote_load(nodes(), Mod).
remote_load/2Loads one or more modules remotely, in a diskless manner.
rpc/1Shorthand for rpc([node()|nodes()], Fun).
rpc/2Shorthand for rpc(Nodes, Fun, infinity).
rpc/3Runs an arbitrary fun (of arity 0) over one or more nodes.
scheduler_usage/1Because Erlang CPU usage as reported from top isn't the most reliable value (due to schedulers doing idle spinning to avoid going to sleep and impacting latency), a metric exists that is based on scheduler wall time.
sctp/0returns a list of all SCTP ports (the data type) open on the node.
source/1Obtain the source code of a module compiled with debug_info.
tcp/0returns a list of all TCP ports (the data type) open on the node.
udp/0returns a list of all UDP ports (the data type) open on the node.

Function Details

bin_leak/1

bin_leak(N::pos_integer()) -> [proc_attrs()]

Refc binaries can be leaking when barely-busy processes route them around and do little else, or when extremely busy processes reach a stable amount of memory allocated and do the vast majority of their work with refc binaries. When this happens, it may take a very long while before references get deallocated and refc binaries get to be garbage collected, leading to Out Of Memory crashes. This function fetches the number of refc binary references in each process of the node, garbage collects them, and compares the resulting number of references in each of them. The function then returns the N processes that freed the biggest amount of binaries, potentially highlighting leaks.

See The efficiency guide for more details on refc binaries

files/0

files() -> [port()]

returns a list of all file handles open on the node.

get_state/1

get_state(PidTerm::pid_term()) -> term()

Shorthand call to recon:get_state(PidTerm, 5000)

get_state/2

get_state(PidTerm::pid_term(), Ms::non_neg_integer() | infinity) -> term()

Fetch the internal state of an OTP process. Calls sys:get_state/2 directly in R16B01+, and fetches it dynamically on older versions of OTP.

inet_count/2

inet_count(AttributeName, Num) -> [inet_attrs()]

Fetches a given attribute from all inet ports (TCP, UDP, SCTP) and returns the biggest Num consumers.

The values to be used can be the number of octets (bytes) sent, received, or both (send_oct, recv_oct, oct, respectively), or the number of packets sent, received, or both (send_cnt, recv_cnt, cnt, respectively). Individual absolute values for each metric will be returned in the 3rd position of the resulting tuple.

inet_window/3

inet_window(AttributeName, Num, Milliseconds) -> [inet_attrs()]

Fetches a given attribute from all inet ports (TCP, UDP, SCTP) and returns the biggest entries, over a sliding time window.

Warning: this function depends on data gathered at two snapshots, and then building a dictionary with entries to differentiate them. This can take a heavy toll on memory when you have many dozens of thousands of ports open.

The values to be used can be the number of octets (bytes) sent, received, or both (send_oct, recv_oct, oct, respectively), or the number of packets sent, received, or both (send_cnt, recv_cnt, cnt, respectively). Individual absolute values for each metric will be returned in the 3rd position of the resulting tuple.

info/1

info(PidTerm::pid_term()) -> [{info_type(), [{info_key(), Value}]}, ...]

Allows to be similar to erlang:process_info/1, but excludes fields such as the mailbox, which have a tendency to grow and be unsafe when called in production systems. Also includes a few more fields than what is usually given (monitors, monitored_by, etc.), and separates the fields in a more readable format based on the type of information contained.

Moreover, it will fetch and read information on local processes that were registered locally (an atom), globally ({global, Name}), or through another registry supported in the {via, Module, Name} syntax (must have a Module:whereis_name/1 function). Pids can also be passed in as a string ("<0.39.0>") or a triple ({0,39,0}) and will be converted to be used.

info/2

info(PidTerm::pid_term(), Keys::info_type()) -> {info_type(), [{info_key(), term()}]}

Allows to be similar to erlang:process_info/2, but allows to sort fields by safe categories and pre-selections, avoiding items such as the mailbox, which may have a tendency to grow and be unsafe when called in production systems.

Moreover, it will fetch and read information on local processes that were registered locally (an atom), globally ({global, Name}), or through another registry supported in the {via, Module, Name} syntax (must have a Module:whereis_name/1 function). Pids can also be passed in as a string ("<0.39.0>") or a triple ({0,39,0}) and will be converted to be used.

Although the type signature doesn't show it in generated documentation, a list of arguments or individual arguments accepted by erlang:process_info/2 and return them as that function would.

A fake attribute binary_memory is also available to return the amount of memory used by refc binaries for a process.

info/3

info(N, N, N) -> [{info_type(), [{info_key(), term()}]}, ...]

Equivalent to info(<A.B.C>) where A, B, and C are integers part of a pid

info/4

info(N, N, N, Key) -> term()

Equivalent to info(<A.B.C>, Key) where A, B, and C are integers part of a pid

named_rpc/1

named_rpc(Fun::fun(() -> term())) -> {[Success::term()], [Fail::term()]}

Shorthand for named_rpc([node()|nodes()], Fun).

named_rpc/2

named_rpc(Nodes::node() | [node(), ...], Fun::fun(() -> term())) -> {[Success::term()], [Fail::term()]}

Shorthand for named_rpc(Nodes, Fun, infinity).

named_rpc/3

named_rpc(Nodes::node() | [node(), ...], Fun::fun(() -> term()), Timeout::timeout()) -> {[Success::term()], [Fail::term()]}

Runs an arbitrary fun (of arity 0) over one or more nodes, and returns the name of the node that computed a given result along with it, in a tuple.

node_stats/4

node_stats(N, Interval, FoldFun, Acc) -> Acc

Gathers statistics N time, waiting Interval milliseconds between each run, and accumulates results using a folding function FoldFun. The function will gather statistics in two forms: Absolutes and Increments.

Absolutes are values that keep changing with time, and are useful to know about as a datapoint: process count, size of the run queue, error_logger queue length, and the memory of the node (total, processes, atoms, binaries, and ets tables).

Increments are values that are mostly useful when compared to a previous one to have an idea what they're doing, because otherwise they'd never stop increasing: bytes in and out of the node, number of garbage colelctor runs, words of memory that were garbage collected, and the global reductions count for the node.

node_stats_list/2

node_stats_list(Repeat, Interval) -> [Stats]

Shorthand for node_stats(N, Interval, fun(X,Acc) -> [X|Acc] end, []) with the results reversed to be in the right temporal order.

node_stats_print/2

node_stats_print(Repeat, Interval) -> term()

Shorthand for node_stats(N, Interval, fun(X,_) -> io:format("~p~n",[X]) end, nostate).

port_info/1

port_info(PortTerm::port_term()) -> [{port_info_type(), [{port_info_key(), term()}]}, ...]

Allows to be similar to erlang:port_info/1, but allows more flexible port usage: usual ports, ports that were registered locally (an atom), ports represented as strings ("#Port<0.2013>"), or through an index lookup (2013, for the same result as "#Port<0.2013>").

Moreover, the function will try to fetch implementation-specific details based on the port type (only inet ports have this feature so far). For example, TCP ports will include information about the remote peer, transfer statistics, and socket options being used.

The information-specific and the basic port info are sorted and categorized in broader categories (port_info_type()).

port_info/2

port_info(PortTerm::port_term(), Keys::port_info_type()) -> {port_info_type(), [{port_info_key(), term()}]}

Allows to be similar to erlang:port_info/2, but allows more flexible port usage: usual ports, ports that were registered locally (an atom), ports represented as strings ("#Port<0.2013>"), or through an index lookup (2013, for the same result as "#Port<0.2013>").

Moreover, the function allows to to fetch information by category as defined in port_info_type(), and although the type signature doesn't show it in the generated documentation, individual items accepted by erlang:port_info/2 are accepted, and lists of them too.

port_types/0

port_types() -> [{Type::string(), Count::pos_integer()}]

Shows a list of all different ports on the node with their respective types.

proc_count/2

proc_count(AttributeName, Num) -> [proc_attrs()]

Fetches a given attribute from all processes and returns the biggest Num consumers.

proc_window/3

proc_window(AttributeName, Num, Milliseconds) -> [proc_attrs()]

Fetches a given attribute from all processes and returns the biggest entries, over a sliding time window.

This function is particularly useful when processes on the node are mostly short-lived, usually too short to inspect through other tools, in order to figure out what kind of processes are eating through a lot resources on a given node.

It is important to see this function as a snapshot over a sliding window. A program's timeline during sampling might look like this:

--w---- [Sample1] ---x-------------y----- [Sample2] ---z--->

Some processes will live between w and die at x, some between y and z, and some between x and y. These samples will not be too significant as they're incomplete. If the majority of your processes run between a time interval x...y (in absolute terms), you should make sure that your sampling time is smaller than this so that for many processes, their lifetime spans the equivalent of w and z. Not doing this can skew the results: long-lived processes, that have 10 times the time to accumulate data (say reductions) will look like bottlenecks when they're not one.

Warning: this function depends on data gathered at two snapshots, and then building a dictionary with entries to differentiate them. This can take a heavy toll on memory when you have many dozens of thousands of processes.

remote_load/1

remote_load(Mod::module()) -> term()

Equivalent to remote_load(nodes(), Mod).

remote_load/2

remote_load(Nodes, Mod::module()) -> term()

Loads one or more modules remotely, in a diskless manner. Allows to share code loaded locally with a remote node that doesn't have it

rpc/1

rpc(Fun::fun(() -> term())) -> {[Success::term()], [Fail::term()]}

Shorthand for rpc([node()|nodes()], Fun).

rpc/2

rpc(Nodes::node() | [node(), ...], Fun::fun(() -> term())) -> {[Success::term()], [Fail::term()]}

Shorthand for rpc(Nodes, Fun, infinity).

rpc/3

rpc(Nodes::node() | [node(), ...], Fun::fun(() -> term()), Timeout::timeout()) -> {[Success::term()], [Fail::term()]}

Runs an arbitrary fun (of arity 0) over one or more nodes.

scheduler_usage/1

scheduler_usage(Millisecs) -> [{SchedulerId, Usage}]

Because Erlang CPU usage as reported from top isn't the most reliable value (due to schedulers doing idle spinning to avoid going to sleep and impacting latency), a metric exists that is based on scheduler wall time.

For any time interval, Scheduler wall time can be used as a measure of how 'busy' a scheduler is. A scheduler is busy when:

A scheduler isn't busy when doing anything else.

sctp/0

sctp() -> [port()]

returns a list of all SCTP ports (the data type) open on the node.

source/1

source(Module::module()) -> iolist()

Obtain the source code of a module compiled with debug_info. The returned list sadly does not allow to format the types and typed records the way they look in the original module, but instead goes to an intermediary form used in the AST. They will still be placed in the right module attributes, however.

tcp/0

tcp() -> [port()]

returns a list of all TCP ports (the data type) open on the node.

udp/0

udp() -> [port()]

returns a list of all UDP ports (the data type) open on the node.