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by noemotion 3072 days ago
>BTW, it's very hard to bring BEAM down. Most exceptions will bring kill the faulty process, but leave the supervisor tree untouched. Only "unmanaged" code (for example, calling a C library using a NIF) might crash the whole VM.

Not completely true. Try to allocate more memory than available and then see what happens.
2 comments
dguaraglia 3072 days ago
I'm actually curious. Do you have some first-hand experience with that kind of issue? I've only played around with Elixir and my only experience deploying BEAM-based applications on production has been RabbitMQ and CouchDB and both of those were very solid.

Also, isn't ENOMEM a standard error that you can handle using the standard error handling techniques?

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noemotion 3072 days ago
I have and it wasn't good. It is impossible to handle out of memory exceptions inside the BEAM. At best, you can hope for a crash of the VM. At worse, it just hangs. And one will most likely not find out about this until they hit this scenario.
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dguaraglia 3072 days ago
Interesting, definitely worth knowing beforehand (I was thinking of implementing a small service that could be pretty memory-intensive using Elixir.) I wonder if there's a way to try and manage memory to avoid ENOMEM.
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lozenge 3072 days ago
If BEAM is allocating memory it must either be copying a message from one process to another, allocating space in a process for its stack, or for some bookkeeping like to spawn a new process. In the first two cases why doesn't it just kill the process and send the usual link and monitor messages to let other Erlang processes handle the failure?
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noemotion 3071 days ago
How would it send a message if it can't allocate memory anymore?
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dguaraglia 3071 days ago
Haha, yeah, that's the problem with ENOMEM handling in general: unless you have a very clear path to free memory immediately and then try to do some reasonable cleanup, you are screwed. Back in the bad old days of running Windows machines with 8mb of memory, I'd religiously handle that kind of error code... but I can't recall the last time I actually bothered. Commoditized hardware makes us lazy.
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keithnoizu 3071 days ago
yeah I have to make liberal use of :hibernate to avoid just this.
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