[R] gc() vs memory.profile()

[Ross Boylan]

I am trying to understand why a function causes my memory use to
explode.  While doing that I noticed that my memory use as reported by
gc() is growing, but the results of memory.profile() are almost
unchanged (the count for raw grew by 3).  How can the two functions
produce different results, and what does it mean?

 >   system.time(r <- Reduce(addResults, bigr[1:10]))                                                                                                                                                                                                                          
    user  system elapsed
   3.437   0.000   3.444
 >   gc()                                                                                                                                                                                                                                                                      
             used   (Mb) gc trigger    (Mb)   max used    (Mb)
 Ncells   2994756  160.0    4418719   236.0    3587436   191.6
 Vcells 797226672 6082.4 2470056017 18845.1 7340162895 56001.0
 > memory.profile()
        NULL      symbol    pairlist     closure environment     promise
           1       13324     1193588       34602        3000        9754
    language     special     builtin        char     logical     integer
      305689          44         637       52237       53954      141713
      double     complex   character         ...         any        list
      548076          38      426187          39           0      116692
  expression    bytecode externalptr     weakref         raw          S4
           1       65604        4195         708         735       23935
 >   system.time(r <- Reduce(addResults, bigr[1:20]))                                                                                                                                                                                                                          
    user  system elapsed
   8.432   0.164  10.315   # suspiciously higher than 2* time for 10
 >   gc()                                                                                                                                                                                                                                                                      
             used   (Mb) gc trigger    (Mb)   max used    (Mb)
 Ncells   2994759  160.0    4418719   236.0    3587436   191.6
!Vcells 828653314 6322.2 2470056017 18845.1 7340162895 56001.0                                                                                                                                                                                                                 
 > memory.profile()
        NULL      symbol    pairlist     closure environment     promise
           1       13324     1193588       34602        3000        9754
    language     special     builtin        char     logical     integer
      305689          44         637       52237       53954      141713
      double     complex   character         ...         any        list
      548076          38      426187          39           0      116692
  expression    bytecode externalptr     weakref         raw          S4
           1       65604        4195         708         738       23935
# by eye, the only change is raw, from 735 to 738.

R 3.0.1 running on Debian GNU/Linux squeeze.

Ross Boylan