[erlang-questions] Fetching several ets keys

Ahmed Omar <>
Thu Feb 9 12:09:21 CET 2012


Hynek,
Yes you are right, if the table is big full scan is not a good idea.

2012/2/9 ori brost <>

> The question is whether there is any way that I can avoid the
> "erlang-to-c call" cost and do these 4 lookups (i.e. with one ets call
> do lookup for all 4).
>
> On Thu, Feb 9, 2012 at 1:00 PM, Hynek Vychodil <> wrote:
> > This code will cause table full scan which usually will be far slower
> than just
> > [ V || K <- ["A","B","C","D"], V <- ets:lookup(Tid, K) ]
> > except very small tables full scan will not be good idea.
> >
> > On Thu, Feb 9, 2012 at 11:49 AM, Ahmed Omar <>
> wrote:
> >> ets:select(Tid, [{{'$1','$2'},[{'==','$1',X}],['$_']}|| X<-
> >> ["A","B","C","D"]]).
> >>
> >>
> >> On Thu, Feb 9, 2012 at 11:11 AM, dmitry kolesnikov <
> >
> >> wrote:
> >>>
> >>> You could try
> >>> ets:select or qlc interface.
> >>>
> >>> It table is not big enough then qlc and custom fold function would
> work:
> >>>
> >>> Q=qlc:q([ X || X <- ets:table(mytab)]),
> >>> qlc:fold(FoldFun, [], Q)
> >>>
> >>> Best Regards,
> >>> Dmitry >-|-|-*>
> >>>
> >>>
> >>> On 9.2.2012, at 11.40, ori brost <> wrote:
> >>>
> >>> > Is there any way in ets to fetch values for several keys in 1 call?
> >>> > i.e. something like
> >>> >
> >>> > ets:multi_fetch(Tid, ["A","B","C","D"]) % will fetch all entries with
> >>> > keys A, B, C, D
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> >
> >
> >
> > --
> > Hynek Vychodil
> > BI consultant
> >
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