Starting mongodb without root permission

mkdir ~/mongodb
# use --fork to run mongodb server as daemon 
mongod --dbpath ~/mongodb/ --fork --logpath ~/mongo/mongodb.log

Summary of concurrency and parallelism in Python

1. For IO bound code, both threading and multiprocessing will work. Multiprocessing is easier to setup using multiprocessing.Pool than threading (with Queue and threading.Thread) , but it has to keep multiple copies of data in memory, resulting in a higher memory overhead.

2. For CPU bound code, multiprocessing is more likely to be better because it has true parallelism. Threading doesn’t in Python due to GIL.

3. For CPU bound code that needs to copy around big chunks of data, which may not fit into the memory, then explicitly share the data using multiprocessing.Value and multiprocessing.Array.

Reference: 

1. A good introduction to the topic, http://www.toptal.com/python/beginners-guide-to-concurrency-and-parallelism-in-python
2. http://stackoverflow.com/questions/14124588/python-multiprocessing-shared-memory

Hadoop tutorial

http://www.thebuttonfactory.nl/?p=1553

I followed it and it works! Ha!

Amber family tree

http://www.zhuyixue.com/amber_tree

Succinct explanation of the relationships between X,X Window ,X11, XFree86 and X.org

http://en.kioskea.net/faq/869-what-is-x-x-window-x11-xfree86-and-x-org

a Chinese one, also fairly clear, but more verbose, and a bit outdated
http://shenlan.blog.51cto.com/55742/441593

helpful comparison of common compression tools

http://blog.terzza.com/linux-compression-comparison-gzip-vs-bzip2-vs-lzma-vs-zip-vs-compress/

my emacs cheatsheet

# using emacs to make a list macro (e.g. 0, 1, 2, 3, 4)
F3 F3  C+n C+a F4

# move point forward to the matching } bracket;
C-M-f

# Insert the output of shell command into emacs buffer
C-u M-! 

# inplace shell command 
M-|

# the following three are for getting help
defun: eldoc                                                                            
C-h f                                                                                     
C-h S

# compilation
emacs --batch --eval '(byte-recompile-directory "~/.emacs.d")'
or to recompile a single file as from a Makefile,
emacs --batch --eval '(byte-compile-file "your-elisp-file.el")'