[erlang-questions] Ref counted binary in ETS

Frank Muller <>
Fri Oct 28 10:00:24 CEST 2016


Crystal clear. Thank you Tony.

Frank.

Le Friday, October 28, 2016, Tony Rogvall <> a écrit :

>
> > On 28 okt 2016, at 06:08, Frank Muller <
> <javascript:;>> wrote:
> >
> > Hmmm ... bigger to  lower the overhead ratio, right?
> >
> Yes. The overhead is fixed.
>
> > Question: is there any (6-words) overhead if a process send 512-bytes
> Bin message to another one?
> >
> Yes.
>
> Every process keeps a list of ProcBins. This structure is kept in order to
> reference count the (global) binary objects.
> After a garbage collection of the heap, that list is swept and binary
> objects not found by the garbage collection are
> dereferenced and the ProcBin is then removed.
> References to the same ProcBin in Erlang code will not create an other
> ProcBin,
> ( the expression Bin2 = Bin1 just copy the reference to the ProcBin )
>
> /Tony
>
> > Frank.
> >
> > Le Friday, October 28, 2016, Tony Rogvall <
> <javascript:;>> a écrit :
> > Simple, you may your 512 byte memory chunks bigger :-)
> >
> > /Tony
> >
> > > On 27 okt 2016, at 23:24, Frank Muller <
> <javascript:;>> wrote:
> > >
> > > Tony,
> > >
> > > Wow, 48-bytes is a huge overhead as N ~= 1000, and Every reader reads
> a binary 10x times or so per second.
> > >
> > > Can anyone please suggest a better strategy to efficiently share them
> with a lesser overhead?
> > >
> > > Frank.
> > >
> > > Le Thursday, October 27, 2016, Tony Rogvall <
> <javascript:;>> a écrit :
> > > 1. A reference.
> > >
> > > It will however build a 6-word structure called ProcBin on the heap
> for every binary reference that you read.
> > > On a 64 bit machine that will lead to a 48 byte overhead. Nearly 10%.
> > >
> > > /Tony
> > >
> > > > On 27 okt 2016, at 20:47, Frank Muller <
> <javascript:;>> wrote:
> > > >
> > > > Hi guys
> > > >
> > > > Suppose an ETS table with only 1 writer and N readers
> > > > This table contains only large binaries (>64B) with the same size
> 512B exactly.
> > > >
> > > > The single writer update these Bins once a while.
> > > > The N readers regularly read one of these Bins, but never
> change/update them.
> > > >
> > > > Questions: what a reader gets when reading a Bin from this ETS table:
> > > >
> > > > 1. a reference to that Bin
> > > > 2. or a full copy of that Bin
> > > >
> > > > Hope someone can clarify this (with an example).
> > > >
> > > > Thank you
> > > > Frank
> > > >
> > > > _______________________________________________
> > > > erlang-questions mailing list
> > > >  <javascript:;>
> > > > http://erlang.org/mailman/listinfo/erlang-questions
> > >
> >
>
>
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