Memory Available for Data Storage

Description

How R manages its workspace.

Details

R has a variable-sized workspace. There are (rarely-used) command-line options to control its minimum size, but no longer any to control the maximum size.

R maintains separate areas for fixed and variable sized objects. The first of these is allocated as an array of 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 heap of ‘Vcells’ of 8 bytes each. Each cons cell occupies 28 bytes on a 32-bit build of R, (usually) 56 bytes on a 64-bit build.

The default values are (currently) an initial setting of 350k cons cells and 6Mb of vector heap. Note that the areas are not actually allocated initially: rather these values are the sizes for triggering garbage collection. These values can be set by the command line options --min-nsize and --min-vsize (or if they are not used, the environment variables R_NSIZE and R_VSIZE) when R is started. Thereafter R will grow or shrink the areas depending on usage, never decreasing below the initial values. The maximal vector heap size can be set with the environment variable R_MAX_VSIZE. An attempt to set a lower maximum than the current usage is ignored. Vector heap limits are given in bytes.

How much time R spends in the garbage collector will depend on these initial settings and on the trade-off the memory manager makes, when memory fills up, between collecting garbage to free up unused memory and growing these areas. The strategy used for growth can be specified by setting the environment variable R_GC_MEM_GROW to an integer value between 0 and 3. This variable is read at start-up. Higher values grow the heap more aggressively, thus reducing garbage collection time but using more memory.

You can find out the current memory consumption (the heap and cons cells used as numbers and megabytes) by typing gc() at the R prompt. Note that following gcinfo(TRUE), automatic garbage collection always prints memory use statistics.

The command-line option --max-ppsize controls the maximum size of the pointer protection stack. This defaults to 50000, but can be increased to allow deep recursion or large and complicated calculations to be done. Note that parts of the garbage collection process goes through the full reserved pointer protection stack and hence becomes slower when the size is increased. Currently the maximum value accepted is 500000.

See Also

An Introduction to R for more command-line options.

Memory-limits for the design limitations.

gc for information on the garbage collector and total memory usage, object.size(a) for the (approximate) size of R object a. memory.profile for profiling the usage of cons cells.