Memory Limits in R

Description

R holds objects it is using in memory. This help file documents the current design limitations on large objects: these differ between 32-bit and 64-bit builds of R.

Details

R holds all objects in memory, and there are limits based on the amount of memory that can be used by all objects:

• There may be limits on the size of the heap and the number of cons cells allowed – see Memory – but these are usually not imposed.
• There is a limit on the address space of a single process such as the R executable. This is 2Gb under 32-bit Windows unless the OS's default has been changed to allow more (up to 3Gb). See http://www.microsoft.com/whdc/system/platform/server/PAE/PAEmem.mspx. (R can be run under Win64 but the 2GB limit applies there and it cannot be increased to 3GB.)
• Under Windows, R does impose limits on the total memory allocation available to a single run, as the OS provides no way to do so. See memory.size and memory.limit.

Error messages beginning cannot allocate vector of size indicate a failure to obtain memory, either because the size exceeded the address-space limit for a process or, more likely, because the system was unable to provide the memory. Note that on a 32-bit OS there may well be enough free memory available, but not a large enough contiguous block of address space into which to map it.

There are also limits on individual objects. On all versions of R, the maximum length (number of elements) of a vector is 2^31 - 1 ~ 2*10^9, as lengths are stored as signed integers. In addition, the storage space cannot exceed the address limit, and if you try to exceed that limit, the error message begins cannot allocate vector of length. The number of characters in a character string is in theory only limited by the address space.

See Also

object.size(a) for the (approximate) size of R object a.