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Re: [long] Mathematica 5.1 and memory: any garbage collection?

• To: mathgroup at smc.vnet.net
• Subject: [mg59724] Re: [mg59697] [long] Mathematica 5.1 and memory: any garbage collection?
• From: ggroup at sarj.ca
• Date: Fri, 19 Aug 2005 04:31:46 -0400 (EDT)
• References: <200508180416.AAA08516@smc.vnet.net>
• Reply-to: ggroup at sarj.ca
• Sender: owner-wri-mathgroup at wolfram.com

On Thursday, August 18, 2005 at 00:16 GMT -0400, Some.Poster heard
voices say:

> My problem lies with the fact that memory used at intermediate stage seems
> never be freed, even whith explicit Clear, Remove or any assignment to {} or
> . in whatever order.

I ran your example and got significantly smaller memory usage (see
below).  Now I ran this on v5, but still 2x10^6 is *much* smaller than
96x10^6. 

> How can one recover the memory freed (if some is ever effectively freed)? Is
> there _any_ garbage collection in the guts of this gazillion dollars piece
> of code?

It seems that the issue is that although you are clearing the
assignment of a value to a variable, you have not unloaded the data
from memory; it is stored in the history.  So it seems that one
solution is to change the $HistoryLength from Infinity to something
smaller.

Below I ran your code as written. I then restarted the kernel, and set
$HistoryLength to 0. Running your code as written didn't change too
dramatically (mind you all my memory usage numbers are far more
reasonable than yours), but there is certainly a difference.

-------------------------Begin-------------------------
In[1]:=
$ProductInformation
Out[1]=
{ProductIDName -> Mathematica, 
    ProductKernelName -> Mathematica 5 Kernel, ProductVersion -> 5.0 for 
    Microsoft Windows (November 18, 2003), ProductVersionNumber -> 5.}

In[2]:=
MemoryInUse[]
Out[2]=
2125192

In[3]:=
(*let's create a moderate - size object*)
try = Tuples[{a, b, c, d, e, f}, 7];
ByteCount[try]
{MemoryInUse[], MaxMemoryUsed[]}
Out[4]=
96
Out[5]=
{2128352, 2169792}

In[6]:=
(*simple mapped function*)
res = Map[2*# &, try];
{MemoryInUse[], MaxMemoryUsed[]}
Out[7]=
{2135056, 2169792}

In[8]:=
(*forgetting a large expression doesn't free _any_ memory*)
try = {};
{MemoryInUse[], MaxMemoryUsed[]}
Out[9]=
{2136784, 2169792}

In[10]:=
(*no more success this way*)
try =.;
{MemoryInUse[], MaxMemoryUsed[]}
Out[11]=
{2138352, 2169792}

In[12]:=
(*... neither a sweep does*)
Clear[try];
{MemoryInUse[], MaxMemoryUsed[]}
Out[13]=
{2140000, 2169792}

In[14]:=
(*... nor a complete wash*)
Remove[try];
{MemoryInUse[], MaxMemoryUsed[]}
Out[15]=
{2141600, 2169792}

In[16]:=
(*freeing the result also seems beyond possible*)
res = {};
{MemoryInUse[], MaxMemoryUsed[]}
Out[17]=
{2143328, 2169792}

In[18]:=
(*still no luck, dad*)
res =.;
{MemoryInUse[], MaxMemoryUsed[]}
Out[19]=
{2141936, 2169792}

In[20]:=
(*ahem, what _is_ Clear supposed to do?*)
Clear[res];
{MemoryInUse[], MaxMemoryUsed[]}
Out[21]=
{2143192, 2169792}

In[22]:=
(*ahem, what _is_ Remove supposed to do?*)
Remove[res];
{MemoryInUse[], MaxMemoryUsed[]}
Out[23]=
{2144440, 2169792}

In[24]:=
Share[]
{MemoryInUse[], MaxMemoryUsed[]}
Out[24]=
120952
Out[25]=
{2024384, 2570200}
--------------------------End--------------------------


-------------------------Begin-------------------------
In[1]:=
$HistoryLength = 0
Out[1]=
0

In[2]:=
$ProductInformation
Out[2]=
{ProductIDName -> Mathematica, 
    ProductKernelName -> Mathematica 5 Kernel, ProductVersion -> 5.0 for 
    Microsoft Windows (November 18, 2003), ProductVersionNumber -> 5.}

In[3]:=
MemoryInUse[]
Out[3]=
2124752

In[4]:=
(*let's create a moderate - size object*)
try = Tuples[{a, b, c, d, e, f}, 7];
ByteCount[try]
{MemoryInUse[], MaxMemoryUsed[]}
Out[5]=
96
Out[6]=
{2130096, 2169824}

In[7]:=
(*simple mapped function*)
res = Map[2*# &, try];
{MemoryInUse[], MaxMemoryUsed[]}
Out[8]=
{2130568, 2169824}

In[9]:=
(*forgetting a large expression doesn't free _any_ memory*)
try = {};
{MemoryInUse[], MaxMemoryUsed[]}
Out[10]=
{2130488, 2169824}

In[11]:=
(*no more success this way*)
try =.;
{MemoryInUse[], MaxMemoryUsed[]}
Out[12]=
{2130488, 2169824}

In[13]:=
(*... neither a sweep does*)
Clear[try];
{MemoryInUse[], MaxMemoryUsed[]}
Out[14]=
{2130488, 2169824}

In[15]:=
(*... nor a complete wash*)
Remove[try];
{MemoryInUse[], MaxMemoryUsed[]}
Out[16]=
{2130376, 2169824}

In[17]:=
(*freeing the result also seems beyond possible*)
res = {};
{MemoryInUse[], MaxMemoryUsed[]}
Out[18]=
{2130104, 2169824}

In[19]:=
(*still no luck, dad*)
res =.;
{MemoryInUse[], MaxMemoryUsed[]}
Out[20]=
{2130104, 2169824}

In[21]:=
(*ahem, what _is_ Clear supposed to do?*)
Clear[res];
{MemoryInUse[], MaxMemoryUsed[]}
Out[22]=
{2130104, 2169824}

In[23]:=
(*ahem, what _is_ Remove supposed to do?*)
Remove[res];
{MemoryInUse[], MaxMemoryUsed[]}
Out[24]=
{2130032, 2169824}

In[25]:=
Share[]
{MemoryInUse[], MaxMemoryUsed[]}
Out[25]=
115280
Out[26]=
{2014464, 2556896}
--------------------------End--------------------------

• References:
  • [long] Mathematica 5.1 and memory: any garbage collection?
    • From: some.poster@use.net