base (version 3.3)

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)
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.

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 Rstarted).

  gcinfo returns the previous value of the flag.

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.

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

Rallocates space for vectors in multiples of 8 bytes: hence the report of "Vcells", a relict 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).

See Also

The R Internals manual.

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

reg.finalizer for actions to happen at garbage collection.

Examples

gc() #- do it now
gcinfo(TRUE) #-- in the future, show when R does it
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)