I had a simple matrix performance rank test that ran fine in version 9.01 on windows 7 up to n=8000. When I run the same test on version 10, when n=7500 Mathematica now started consuming all memory on the PC (I have 16 GB of ram) and actually the whole PC hanged for long time. I can hear the disk thrashing and the whole process was very bad. After 30 minutes or so, I was about to reboot the PC. But was finally able to access the task manager and terminate Mathematica process.
The test is simple, here it is
Remove["Global`*"];
Share[];
n = 7500; (*values above hanged my PC*)
m = Table[Random[], {i, 1, n}, {j, 1, n}];
AbsoluteTiming[MatrixRank[m];]
I also noticed this memory problem on other tests. I have a large differential equation test case where Mathematica hanged on many cases. All memory issues. I do not know what changed. As I said, I run the same test, on the same exact PC with version 9. To see more details of the test, here is a link
May be someone can investigate this more or have an idea what is the problem. Does this problem also show up on the Mac? What about Linux?
Warning: Do not run the above on your PC without first saving all you work, all you documents from other application. Mathematica can and will hang the PC unless you have zillion GB of memory. I am going to buy more memory myself and add another 16 GB and try this test again.
But for me, this is a regression in Mathematica performance from version 9.01. A small follow up question: Is there a way to tell Mathematica, as a global options or setting, not to use system memory more than some limit? For example, tell it to terminate any computation if Mathematica process (FF or Kernel) has allocated more than say 6GB or memory). If there is such a way, then I can set this limit in my preferences and not have to worry about the possibility of running out of PC memory again when using Mathematica. I assume Mathematica internally is able to determine how much system RAM is consumed at any one point.