LFE and ETS ...

[Duncan McGreggor]

I don't know if I've ever played with ETS before in LFE ... definitely Mnesia, but I can't remember using ETS before.

So, naturally, I have some questions :-)

Something that I noticed in the LFE REPL: when getting an exception error (e.g., calling an Erlang stdlib mod:func with args in the wrong order), I could no longer access my ETS table. Upon digging, I saw that the LFE pid was changing every time an exception was thrown. Is that new with 1.3? (To date, most of my LFE use has been pre-1.0, and the remainder has been with 1.2) Maybe the pid has changed every time there was an exception in the REPL, and this is the first time I've noticed (or I have forgotten!)?

Seeing this, of course, made sense of the ETS table going away, since that's tied to the process that starts it. Not a biggie, though -- I'm exploring storing config data for a library in ETS, to take lookups off the filesystem. If the process crashes, I can just re-read from disk ...

d

[Fred Hebert]

The Erlang shell  works the same way. Usually people will use a worker or supervisor to own the ETS table and make sure it won’t crash. If t does crash, there’s the ability to set heirs and give tables away as well.

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[Duncan McGreggor]

Perfect, Fred -- thanks! (and, yeah -- that's the approach I'm using for the lib: the supervisor is going to create the table).

Oh, wow ... I _didn't_ know about setting heirs and giving tables away; VERY cool. I'll re-read (well read instead of skim) the Bears-ETS-Beets chapter to see where I missed that ...

THANKS!

d

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[Dave Cottlehuber]

On Mon, 20 May 2019, at 17:07, Duncan McGreggor wrote:
> Perfect, Fred -- thanks! (and, yeah -- that's the approach I'm using
> for the lib: the supervisor is going to create the table).
>
> Oh, wow ... I _didn't_ know about setting heirs and giving tables away;
> VERY cool. I'll re-read (well read instead of skim) the Bears-ETS-Beets
> chapter to see where I missed that ...
>
> THANKS!
>
> d

There's some prior art if that helps.

https://steve.vinoski.net/blog/2011/03/23/dont-lose-your-ets-tables/
https://github.com/DeadZen/etsgive & https://github.com/whitfin/eternal are my favourites

A+
Dave

[Robert Virding]

Yes, I modelled (copied) the LFE repl on the Erlang shell. They seem more processy than the Elixir shell which doesn't die as often.

Robert

On Monday, 20 May 2019 17:59:24 UTC+2, Fred Hebert wrote:

The Erlang shell  works the same way. Usually people will use a worker or supervisor to own the ETS table and make sure it won’t crash. If t does crash, there’s the ability to set heirs and give tables away as well.

On Sun, May 19, 2019 at 22:33 Duncan McGreggor <dun...@mcgreggor.org> wrote:

I don't know if I've ever played with ETS before in LFE ... definitely Mnesia, but I can't remember using ETS before.

So, naturally, I have some questions :-)

Something that I noticed in the LFE REPL: when getting an exception error (e.g., calling an Erlang stdlib mod:func with args in the wrong order), I could no longer access my ETS table. Upon digging, I saw that the LFE pid was changing every time an exception was thrown. Is that new with 1.3? (To date, most of my LFE use has been pre-1.0, and the remainder has been with 1.2) Maybe the pid has changed every time there was an exception in the REPL, and this is the first time I've noticed (or I have forgotten!)?

Seeing this, of course, made sense of the ETS table going away, since that's tied to the process that starts it. Not a biggie, though -- I'm exploring storing config data for a library in ETS, to take lookups off the filesystem. If the process crashes, I can just re-read from disk ...

d

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