Removes cached results from build_primary_production(),
build_commodity_balances(), and build_processing_coefs()
so that the next call rebuilds from scratch.
Memory that clearing the cache does not return
Clearing the cache releases the cached tibbles to R, but the process may
keep far more resident memory than it holds. That excess is not held by
the cache or by any reachable object, so neither this function nor
gc() recovers it (whep#777).
It is memory R has already freed and the C allocator keeps. On Linux, glibc serves a large allocation with its own mapping, which goes back to the operating system on free, only while it is bigger than the "mmap threshold". Each such free raises that threshold (up to 32 MB), so later vectors below it come from the heap, and freed heap blocks stay resident. The build chain frees many vectors of that size.
Measured with get_primary_production() and get_wide_cbs() for
2008-2012, after gc(), holding 1.17 GB of live R objects: 5.5-5.8 GB
resident by default, 3.3 GB with a fixed threshold, identical outputs.
Fixing the threshold switches the raising off. glibc reads it when the
process starts, so it must be set in the shell that launches R, not in
.Renviron:
Other platforms and allocators are unaffected by the variable.