gc Garbage Collection

Description

A call of gc causes a garbage collection to take place. gcinfo sets a flag so that automatic collection is either silent (verbose = FALSE) or prints memory usage statistics (verbose = TRUE).

Usage

gc(verbose = getOption("verbose"), reset = FALSE, full = TRUE)
gcinfo(verbose)

Arguments

verbose	logical; if TRUE, the garbage collection prints statistics about cons cells and the space allocated for vectors.
reset	logical; if TRUE the values for maximum space used are reset to the current values.
full	logical; if TRUE a full collection is performed; otherwise only more recently allocated objects may be collected.

Details

A call of gc causes a garbage collection to take place. This will also take place automatically without user intervention, and the primary purpose of calling gc is for the report on memory usage. For an accurate report full = TRUE should be used.

It can be useful to call gc after a large object has been removed, as this may prompt R to return memory to the operating system.

R allocates space for vectors in multiples of 8 bytes: hence the report of "Vcells", a relic of an earlier allocator (that used a vector heap).

When gcinfo(TRUE) is in force, messages are sent to the message connection at each garbage collection of the form

    Garbage collection 12 = 10+0+2 (level 0) ...
    6.4 Mbytes of cons cells used (58%)
    2.0 Mbytes of vectors used (32%)

Here the last two lines give the current memory usage rounded up to the next 0.1Mb and as a percentage of the current trigger value. The first line gives a breakdown of the number of garbage collections at various levels (for an explanation see the ‘R Internals’ manual).

Value

gc returns a matrix with rows "Ncells" (cons cells), usually 28 bytes each on 32-bit systems and 56 bytes on 64-bit systems, and "Vcells" (vector cells, 8 bytes each), and columns "used" and "gc trigger", each also interpreted in megabytes (rounded up to the next 0.1Mb).

If maxima have been set for either "Ncells" or "Vcells", a fifth column is printed giving the current limits in Mb (with NA denoting no limit).

The final two columns show the maximum space used since the last call to gc(reset = TRUE) (or since R started).

gcinfo returns the previous value of the flag.

See Also

The ‘R Internals’ manual.

Memory on R's memory management, and gctorture if you are an R developer.

gc.time() reports time used for garbage collection.

reg.finalizer for actions to happen at garbage collection.

Examples

gc() #- do it now
gcinfo(TRUE) #-- in the future, show when R does it
##            vvvvv use larger to *show* something
x <- integer(100000); for(i in 1:18) x <- c(x, i)
gcinfo(verbose = FALSE) #-- don't show it anymore

gc(TRUE)

gc(reset = TRUE)