[erlang-questions] Ref counted binary in ETS

Tony Rogvall <>
Fri Oct 28 09:53:19 CEST 2016


> On 28 okt 2016, at 06:08, Frank Muller <> 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 <> a écrit :
> Simple, you may your 512 byte memory chunks bigger :-)
> 
> /Tony
> 
> > On 27 okt 2016, at 23:24, Frank Muller <> 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 <> 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 <> 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
> > > 
> > > http://erlang.org/mailman/listinfo/erlang-questions
> >
> 

-------------- next part --------------
A non-text attachment was scrubbed...
Name: signature.asc
Type: application/pgp-signature
Size: 801 bytes
Desc: Message signed with OpenPGP using GPGMail
URL: <http://erlang.org/pipermail/erlang-questions/attachments/20161028/1f164bf2/attachment.bin>


More information about the erlang-questions mailing list