\name{Memory}
\alias{Memory}
\alias{mem.limits}
\title{Memory Available for Data Storage}
\description{
  Use command line options to control the memory available for \R.
}
\usage{
#ifdef unix
R --min-vsize=vl --max-vsize=vu --min-nsize=nl --max-nsize=nu
#endif
#ifdef windows
Rgui --min-vsize=vl --max-vsize=vu --min-nsize=nl --max-nsize=nu
Rterm --min-vsize=vl --max-vsize=vu --min-nsize=nl --max-nsize=nu
#endif

mem.limits(nsize = NA, vsize = NA)
}
\arguments{
  \item{vl, vu, vsize}{Heap memory in bytes.}
  \item{nl, nu, nsize}{Number of cons cells.}
}
\details{
  \R has a variable-sized workspace (from version 1.2.0). There is now
  much less need to set memory options than previously, and most
  users will never need to set these.  They are provided both as a way
  to control the overall memory usage (which can also be done
#ifdef unix
  by operating-system facilities such as \code{limit} on Unix),
#endif
#ifdef windows
  using the option \option{--max-mem-size} on Windows),
#endif
  and since setting larger values of the minima will make \R slightly
  more efficient on large tasks.

#ifdef windows
  (On Windows the \option{--max-mem-size} option sets the maximum memory
  allocation: it has a minimum allowed value of 16M.  This is intended
  to catch attempts to allocate excessive amounts of memory which may
  cause other processes to run out of resources.  The default is the
  smaller of the amount of physical RAM in the machine and 1024Mb.
  See also \code{\link[utils]{memory.limit}}.)
#endif

  To understand the options, one needs to know that \R maintains
  separate areas for fixed and variable sized objects.  The first of these
  is allocated as an array of \dQuote{\emph{cons cells}} (Lisp programmers will
  know what they are, others may think of them as the building blocks of
  the language itself, parse trees, etc.), and the second are thrown on a
  \dQuote{\emph{heap}} of \dQuote{Vcells} of 8 bytes each.  Effectively,
  the input \code{v} is rounded up to the nearest multiple of 8.

  Each cons cell occupies 28 bytes on a 32-bit machine, (usually) 56 bytes
  on a 64-bit machine.

  The \option{--*-nsize} options can be used to specify the number of
  cons cells and the \option{--*-vsize} options specify the size of the
  vector heap in bytes.  Both options must be integers or integers
  followed by \code{G}, \code{M}, \code{K}, or \code{k} meaning
  \code{Giga} (\eqn{2^{30} = 1073741824}) \emph{Mega} (\eqn{2^{20} =
    1048576}), (computer) \emph{Kilo} (\eqn{2^{10} = 1024}), or regular
  \emph{kilo} (1000).

  The \option{--min-*} options set the minimal sizes for the number of
  cons cells and for the vector heap.  These values are also the initial
  values, but thereafter \R will grow or shrink the areas depending on
  usage, but never exceeding the limits set by the \option{--max-*}
  options nor decreasing below the initial values.

  The default values are currently minima of 350k cons cells,
  6Mb of vector heap
  and no maxima (other than machine resources). The maxima can be
  changed during an \R session by calling \code{mem.limits}. (If this is
  called with the default values, it reports the current settings.)


  You can find out the current memory consumption (the heap and cons
  cells used as numbers and megabytes) by typing \code{\link{gc}()} at the
  \R prompt.  Note that following \code{\link{gcinfo}(TRUE)}, automatic
  garbage collection always prints memory use statistics.  Maxima will
  never be reduced below the current values for triggering garbage
  collection, and attempts to do so will be silently ignored.

%  The defaults for \option{--min-nsize} and \option{--min-vsize} can be
%  changed by setting the environment variables \env{R\_NSIZE} and
%  \env{R\_VSIZE} respectively, perhaps most conveniently in the file
%  \file{.Renviron} or \file{\eqn{\sim}{~}/.Renviron}.  There should no
%  longer be any need to do so.

  When using \code{\link{read.table}}, the memory requirements are in
  fact higher than anticipated, because the file is first read in as one
  long string which is then split again.  Use \code{\link{scan}} if
  possible in case you run out of memory when reading in a large table.
}

\value{
  \code{mem.limits()} returns an integer vector giving the current
  settings of the maxima, possibly \code{NA}.
}

\seealso{
  \code{\link{gc}} for information on the garbage collector,
  \code{\link[utils]{object.size}(a)} for the (approximate) size of \R object
  \code{a}.  \code{\link{memory.profile}} for profiling the usage of
  cons cells.
#ifdef windows

  \code{\link[utils]{memory.size}} to monitor total memory usage,
  \code{\link[utils]{memory.limit}} for the current limit.
#endif
}

\note{
  For backwards compatibility, options \option{--nsize} and
  \option{--vsize} are equivalent to \option{--min-nsize} and
  \option{--min-vsize}.
#ifdef windows

  When using the \code{Rgui} console it is simplest to make a shortcut and
  put these command-line flags at the end of the Target field.
#endif
}

\examples{
# Start R with 10MB of heap memory and 500k cons cells, limit to
# 100Mb and 1M cells
\dontrun{
## Unix
R --min-vsize=10M --max-vsize=100M --min-nsize=500k --max-nsize=1M
}
}
\keyword{environment}
