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).
gc(verbose = getOption("verbose"), reset = FALSE, full = TRUE)
gcinfo(verbose)logical; if TRUE, the garbage collection prints
statistics about cons cells and the space allocated for vectors.
logical; if TRUE the values for maximum space used
are reset to the current values.
logical; if TRUE a full collection is performed;
otherwise only more recently allocated objects may be collected.
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.
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).
The ‘R Internals’ manual.
Memory on R's memory management,
and gctorture if you are an R developer.
reg.finalizer for actions to happen at garbage
collection.
# NOT RUN {
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)
# }
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