[erlang-questions] Cross OTP version compare-and-swap semantic on ETS
Thu Oct 12 13:44:32 CEST 2017
On 10/12/2017 01:15 PM, Benoit Chesneau wrote:
> Thanks for the answer :)
>> On 12 Oct 2017, at 10:17, Chandru
>> <mailto:chandrashekhar.mullaparthi@REDACTED>> wrote:
>> On 12 October 2017 at 09:01, Benoit Chesneau <bchesneau@REDACTED
>> <mailto:bchesneau@REDACTED>> wrote:
>> Hi all,
>> I’m looking on the best way (in term of concurrency and response
>> speed) to provide a equivalent of compare-and-swap semantic on
>> differs Erlang version with ETS.
>> For now what I do is using `select_replace/2` on OTP 20 and for
>> other versions I’m using a pen_server to serialise the writes on
>> this values, making this gen_server a bottle neck. Which is fine
>> for a small list of keys to update. I didn’t find any other
>> solution to do it right now. But maybe someone has an idea?
>> The only thing I can think of is to partition the key space and use
>> multiple ETS tables (with a dedicated process for each).
> True. I can do that indeed … That may be the easiest thing to do in
> the long term.
> For now I I did this simple lib:
> https://gitlab.com/barrel-db/lab/ets_cas with limited test coverage.
>> Also something I’m currently missing is the possibility do the
>> dame for delete. `select_delete` isn’t atomic right?
>> Not sure what you mean by 'atomic' here. I expect ETS will delete
>> whatever entries have matched this specified pattern at that point in
>> time. In the context of ETS operations, the consideration of whether
>> it is 'atomic' or not makes sense in the 'insert', 'replace' or
>> 'update' scenario.
> I’m not sure what’s the difference between a delete and a replace
> there with the current ETS librarie 20.1 . By atomic I mean atomic at
> the key level, ie 2 concurrent delete will be serialisable which
> seems to be the case for `select_replace` .
All ets:select* functions are atomic per table object.
That is, each match-and-* operation is atomic. The iteration is not.
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