On 1/22/19 6:17 PM, Kevin Ushey wrote:
I think that object.size() is most commonly used to answer the question,
"what R objects are consuming the most memory currently in my R session?"
and for that reason I think returning the size of the internal
representations of objects (for e.g. ALTREP objects; unevaluated promises)
is the right default behavior.
I don't think one could answer that question at all in the presence of
sharing (of objects with value semantics due to copy on write, string
cache or other caches, sharing of objects with referential semantics
such as environments, etc). Also the mapping from R objects (SEXPs) to
what users might understand as objects would not be clear (which SEXPs
belong to which "object", which SEXPs are too low-level for the user to
be considered, etc). In principle, there could be a memory profiler
working at SEXP level and exposing all the intricacies of the memory
layout, answering reachability questions on a heap dump (so one could
find out about a 1G integer vector and then list all bindings say in
namespace environments from which it is reachable), but of course that
would be a lot of work to implement and to maintain. The problem is not
unique to R (e.g. see Java with the same problems of sharing that
prevent meaningful definition for object size). I am not persuaded it
makes sense to add more options to a function that does not have and
cannot have a well defined user-level semantics, and I would discourage
writing code that is trying to build on that function as I think that it
might lead to confusion and frustration. I think equality for example is
easier to define (just that one could come up with multiple meaningful
definitions, so it makes sense to have multiple options).
Best
Tomas
I also agree it would be worth considering adding arguments that control
how object.size() is computed for different kinds of R objects, since users
might want to use object.size() to answer different types of questions.
All that said, if the ultimate goal here is to avoid having RStudio
materialize ALTREP objects in the background, then perhaps that change
should happen in RStudio :-)
Best,
Kevin
On Tue, Jan 22, 2019 at 8:21 AM Tierney, Luke <luke-tier...@uiowa.edu>
wrote:
On Mon, 21 Jan 2019, Martin Maechler wrote:
Travers Ching
on Tue, 15 Jan 2019 12:50:45 -0800 writes:
> I have a toy alt-rep string package that generates
> randomly seeded strings. example: library(altstringisode)
> x <- altrandomStrings(1e8) head(x) [1]
> "2PN0bdwPY7CA8M06zVKEkhHgZVgtV1"
> "5PN2qmWqBlQ9wQj99nsQzldVI5ZuGX" ... etc object.size(1e8)
> Object.size will call the set_altstring_Elt_method for
> every single element, materializing (slowly) every element
> of the vector. This is a problem mostly in R-studio since
> object.size is called automatically, defeating the purpose
> of alt-rep.
There is no sensible way in general to figure out how large the
strings would be without computing them. There might be specifically
for a deferred sequence conversion but it would require a fair bit of
effort to figure out that would be better spent elsewhere.
I've never been a big fan of object.size since what it is trying to
compute isn't very well defined in the context of sharing and possible
internal state changes (even before ALTREP byte code compilation could
change the internals of a function [which object.size sees] and
assigning into environments or evaluating promises can change
environments [which object.size ignores]). The issue is not unlike the
one faced by identical(), which has a bunch of options for the
different ways objects can be identical, and might need even more.
We could in general have object.size for and ALTREP return the
object.size results of the current internal representation, but that
might not always be appropriate. Again, what object.size is trying to
compute isn't very well defined.
RStudio does seem to call object.size on every assignment to
.GlobalEnv. That might be worth revisiting.
Best,
luke
Hmm. But still, the idea had been that object.size() *shuld*
return the size of the "de-ALTREP'ed" object *but* should not
de-ALTREP it.
That's what happens for integers, but indeed fails to happen for
such as.character(.)ed integers.
From my eRum presentation (which took from the official ALTREP
documentation
https://svn.r-project.org/R/branches/ALTREP/ALTREP.html ) :
> x <- 1:1e15
> object.size(x) # 8000'000'000'000'048 bytes : 8000 TBytes -- ok, not
really
8000000000000048 bytes
> is.unsorted(x) # FALSE : i.e., R's *knows* it is sorted
[1] FALSE
> xs <- sort(x) #
> .Internal(inspect(x))
@80255f8 14 REALSXP g0c0 [NAM(7)] 1 : 1000000000000000 (compact)
>
> cx <- as.character(x)
> .Internal(inspect(cx))
@80485d8 16 STRSXP g0c0 [NAM(1)] <deferred string conversion>
@80255f8 14 REALSXP g1c0 [MARK,NAM(7)] 1 : 1000000000000000 (compact)
> system.time( print(object.size(x)), gc=FALSE)
8000000000000048 bytes
user system elapsed
0.000 0.000 0.001
> system.time( print(object.size(cx)), gc=FALSE)
Error: cannot allocate vector of size 8388608.0 Gb
Timing stopped at: 11.43 0 11.46
>
One could consider it a bug that object.size(cx) is indeed
inspecting every string, i.e., accessing cx[i] for all i.
Note that it is *not* deALTREPing cx itself :
x <- 1:1e6
cx <- as.character(x)
.Internal(inspect(cx))
@7f5b1a0 16 STRSXP g0c0 [NAM(1)] <deferred string conversion>
@7f5adb0 13 INTSXP g0c0 [NAM(7)] 1 : 1000000 (compact)
system.time( print(object.size(cx)), gc=FALSE)
64000048 bytes
user system elapsed
0.369 0.005 0.374
.Internal(inspect(cx))
@7f5b1a0 16 STRSXP g0c0 [NAM(7)] <deferred string conversion>
@7f5adb0 13 INTSXP g0c0 [NAM(7)] 1 : 1000000 (compact)
> Is there a way to avoid the problem of forced
> materialization in rstudio?
> PS: Is there a way to tell if a post has been received by
> the mailing list? How long does it take to show up in the
> archives?
[ that (waiting time) distribution is quite right skewed... I'd
guess it's median to be less than 10 minutes... but we had
artificially delayed it somewhat in the past to fight
spammers, and ETH (the hosting instituttion) and others have
increased spam and virus filtering so everything has become
quite a bit slower ]
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Luke Tierney
Ralph E. Wareham Professor of Mathematical Sciences
University of Iowa Phone: 319-335-3386
Department of Statistics and Fax: 319-335-3017
Actuarial Science
241 Schaeffer Hall email: luke-tier...@uiowa.edu
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