[Solr Wiki] Update of "SolrPerformanceProblems" by ShawnHeisey

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The "SolrPerformanceProblems" page has been changed by ShawnHeisey:
https://wiki.apache.org/solr/SolrPerformanceProblems?action=diff&rev1=84&rev2=85

Comment:
Added information about getting a process listing to answer questions about memory.

  
  One potential problem with SSD is that operating system TRIM support is required for good long-term performance.  For single disks, TRIM is usually well supported, but if you want to add any kind of hardware RAID (and most software RAID as well), TRIM support disappears.   At the time of this writing, it seems that only Intel supports a solution and that is [[http://www.anandtech.com/show/6161/intel-brings-trim-to-raid0-ssd-arrays-on-7series-motherboards-we-test-it|limited to Windows 7 or later and RAID 0]].  One way to make this less of a problem with Solr is to put your OS and Solr itself on a RAID of regular disks, and put your index data on a lone SSD.  If the SSD fails, your redundant server(s) will still be there to handle requests.
  
+ === Asking for help on a memory/performance issue ===
+ 
+ If you ask for help on an issue you're having with performance, which will typically take place either on the solr-user mailing list or the #solr IRC channel, one of the first things that needs to be determined is whether you have enough memory for reasonable performance.  Getting certain information from the OS will help determine this.  A screenshot of your process information, sorted by memory usage, can answer most of the questions that residents of the mailing list or IRC channel will have.
+ 
+ ==== Process listing on POSIX operating systems ====
+ 
+ This will involve the utility named "top".  There are some other variants of this program available, like htop, which do not provide the information desired.  Run the "top" utility.  If it's the version of top produced by the Gnu project, you can press shift-M to sort the listing by RES memory, descending.  If it's another version of top, getting the appropriate sort may require research.  Once the correct sort is achieved, grab a screenshot.  Share the screenshot with a file sharing website.
+ 
+ ==== Process listing on Windows ====
+ 
+ This will only work on recent versions of Windows.  Hopefully it will be a Server edition, 2008 or newer, 64-bit.  Run the program named Resource Monitor. Click on the Memory tab, then resize the window and the columns so that things can be seen clearly.  Click on the "Working Set" column until the sort is descending within that column.   Grab a screenshot.  If you press Alt-PrintScreen the contents of the window will end up in the clipboard and you can paste them into a program like Paint.  Share the screenshot with a file sharing website.
+ 
  == Extreme scaling ==
  
  Hardware requirements start to become extreme when the Solr index reaches billions of documents and hundreds of gigabytes, *especially* if there is a high query rate.  Handling indexes of this size becomes very expensive, because it usually requires a lot of servers that each have a lot of memory.  SSD becomes even more critical, which drives the cost up.