From 6912c3db95b4ca0d78b5c388daae262321645624 Mon Sep 17 00:00:00 2001 From: =?UTF-8?q?Bj=C3=B6rn-Egil=20Dahlberg?= Date: Fri, 20 Jan 2017 14:12:18 +0100 Subject: otp: Don't mention percept in documentation --- system/doc/efficiency_guide/processes.xml | 4 ---- 1 file changed, 4 deletions(-) (limited to 'system') diff --git a/system/doc/efficiency_guide/processes.xml b/system/doc/efficiency_guide/processes.xml index f2d9712f51..b9982353be 100644 --- a/system/doc/efficiency_guide/processes.xml +++ b/system/doc/efficiency_guide/processes.xml @@ -261,10 +261,6 @@ true The estone benchmark, for example, is entirely sequential. So is the most common implementation of the "ring benchmark"; usually one process is active, while the others wait in a receive statement.

- -

The percept application - can be used to profile your application to see how much potential (or lack - thereof) it has for concurrency.

-- cgit v1.2.3 From 1bcacc64d5f33d674fa50c85ed9a982ade380bd5 Mon Sep 17 00:00:00 2001 From: Richard Carlsson Date: Fri, 16 Dec 2016 11:40:38 +0100 Subject: Add design principles restart intensity howto --- system/doc/design_principles/sup_princ.xml | 63 ++++++++++++++++++++++++++++++ 1 file changed, 63 insertions(+) (limited to 'system') diff --git a/system/doc/design_principles/sup_princ.xml b/system/doc/design_principles/sup_princ.xml index c24177d842..478d1bf714 100644 --- a/system/doc/design_principles/sup_princ.xml +++ b/system/doc/design_principles/sup_princ.xml @@ -175,6 +175,69 @@ SupFlags = #{intensity => MaxR, period => MaxT, ...}

The keys intensity and period are optional in the supervisor flags map. If they are not given, they default to 1 and 5, respectively.

+
+ Tuning the intensity and period +

The default values are 1 restart per 5 seconds. This was chosen to + be safe for most systems, even with deep supervision hierarchies, + but you will probably want to tune the settings for your particular + use case.

+

First, the intensity decides how big bursts of restarts you want + to tolerate. For example, you might want to accept a burst of at + most 5 or 10 attempts, even within the same second, if it results + in a successful restart.

+

Second, you need to consider the sustained failure rate, if + crashes keep happening but not often enough to make the supervisor + give up. If you set intensity to 10 and set the period as low as 1, + the supervisor will allow child processes to keep restarting up to + 10 times per second, forever, filling your logs with crash reports + until someone intervenes manually.

+

You should therefore set the period to be long enough that you can + accept that the supervisor keeps going at that rate. For example, + if you have picked an intensity value of 5, then setting the period + to 30 seconds will give you at most one restart per 6 seconds for + any longer period of time, which means that your logs won't fill up + too quickly, and you will have a chance to observe the failures and + apply a fix.

+

These choices depend a lot on your problem domain. If you don't + have real time monitoring and ability to fix problems quickly, for + example in an embedded system, you might want to accept at most + one restart per minute before the supervisor should give up and + escalate to the next level to try to clear the error automatically. + On the other hand, if it is more important that you keep trying + even at a high failure rate, you might want a sustained rate of as + much as 1-2 restarts per second.

+

Avoiding common mistakes: + + +

Do not forget to consider the burst rate. If you set intensity + to 1 and period to 6, it gives the same sustained error rate as + 5/30 or 10/60, but will not allow even 2 restart attempts in + quick succession. This is probably not what you wanted.

+ + +

Do not set the period to a very high value if you want to + tolerate bursts. If you set intensity to 5 and period to 3600 + (one hour), the supervisor will allow a short burst of 5 + restarts, but then gives up if it sees another single restart + almost an hour later. You probably want to regard those crashes + as separate incidents, so setting the period to 5 or 10 minutes + will be more reasonable.

+ + +

If your application has multiple levels of supervision, then + do not simply set the restart intensities to the same values on + all levels. Keep in mind that the total number of restarts + (before the top level supervisor gives up and terminates the + application) will be the product of the intensity values of all + the supervisors above the failing child process.

+

For example, if the top level allows 10 restarts, and the next + level also allows 10, a crashing child below that level will be + restarted 100 times, which is probably excessive. Allowing at + most 3 restarts for the top level supervisor might be a better + choice in this case.

+ +

+
-- cgit v1.2.3 From bbc16d5c48cb8657214a270f899cb37834d7d744 Mon Sep 17 00:00:00 2001 From: Kim Shrier Date: Wed, 1 Feb 2017 23:07:23 -0700 Subject: fix a few statem typos --- system/doc/design_principles/statem.xml | 4 ++-- 1 file changed, 2 insertions(+), 2 deletions(-) (limited to 'system') diff --git a/system/doc/design_principles/statem.xml b/system/doc/design_principles/statem.xml index f627145f9f..d08ddd0036 100644 --- a/system/doc/design_principles/statem.xml +++ b/system/doc/design_principles/statem.xml @@ -130,7 +130,7 @@ handle_event(EventType, EventContent, State, Data) -> {next_state, NewState, NewData}

- Se section + See section One Event Handler for an example.

@@ -887,7 +887,7 @@ stop() ->

This type of time-out is useful to for example act on inactivity. - Let us start restart the code sequence + Let us restart the code sequence if no button is pressed for say 30 seconds:

Date: Tue, 14 Feb 2017 11:30:58 +0200 Subject: Fixed typos in system/doc --- system/doc/efficiency_guide/bench.erl | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) (limited to 'system') diff --git a/system/doc/efficiency_guide/bench.erl b/system/doc/efficiency_guide/bench.erl index 1f60e858f6..a1be24b051 100644 --- a/system/doc/efficiency_guide/bench.erl +++ b/system/doc/efficiency_guide/bench.erl @@ -355,7 +355,7 @@ create_html_report(ResultList) -> {ok, OutputFile} = file:open("index.html", [write]), - %% Create the begining of the result html-file. + %% Create the beginning of the result html-file. Head = Title = "Benchmark Results", io:put_chars(OutputFile, "\n"), io:put_chars(OutputFile, "\n"), -- cgit v1.2.3