Question

I’ve been learning how to use ets, but one thing that has bothered me is that, occasionally*, ets:match throws a bad argument… And, from them on, all subsequent calls (even calls which previously worked) also throw a bad argument:

> ets:match(Tid, { [$r | '$1'] }, 1).
% this match works...
% Then, at some point, this comes up:
** exception error: bad argument
     in function  ets:match/3
        called as ets:match(24589,{[114|'$1']},1)
% And from then on, matches stop working:
> ets:match(Tid, { [$r | '$1'] }, 1).
** exception error: bad argument
     in function  ets:match/3
        called as ets:match(24589,{[114|'$1']},1)

Is there any way to “reset” the ets system so that I can query it (ie, from the shell) again?

*: I haven’t been able to reproduce the problem… But it happens fairly often while I’m trying to do “other things”.

Answer 1

Although I’m not 100% sure, this thread seems to answer your question. It appears that you’re observing this behaviour in the shell. If so, two facts are interacting in a confusing way:

1. An ets table is deleted as soon as its owning process dies.
2. The erlang shell dies whenver it receives an exception and is silently restarted.

So, when you get the first exception, the current shell process dies causing the ets table to be deleted, and then a new shell process is started for you. Now, when you try another ets:match, it fails because the table no longer exists.