osx mysql2 mysql.h is missing.

Taken directly from Stackoverflow (http://stackoverflow.com/a/17262871/80492)

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What worked for me in Mountain Lion Rails install(using Homebrew and RVM) was editing /usr/local/Cellar/mysql/5.XX.XX/bin/mysql_config and removing -Wno-null-conversion -Wno-unused-private-field from cxflags and cxflags options as follows:

Before:

cflags="-I$pkgincludedir  -Wall -Wno-null-conversion -Wno-unused-private-field -Os -g -fno-strict-aliasing -DDBUG_OFF " #note: end space!
cxxflags="-I$pkgincludedir  -Wall -Wno-null-conversion -Wno-unused-private-field -Os -g -fno-strict-aliasing -DDBUG_OFF " #note: end space!

After:

cflags="-I$pkgincludedir  -Wall -Os -g -fno-strict-aliasing -DDBUG_OFF " #note: end space!
cxxflags="-I$pkgincludedir  -Wall -Os -g -fno-strict-aliasing -DDBUG_OFF " #note: end space!

After that gem install mysql2 proceeded without hickups

Sphinx fails to start with rake ts:start or rake ts:rebuild

$ rake ts:start
Failed to start searchd daemon. Check ../log/searchd.log.
Failed to start searchd daemon. Check ../log/searchd.log
Be sure to run thinking_sphinx:index before thinking_sphinx:start

Almost always is the case for me that searchd is already running / orphaned and needs to be killed. Run

$ps -ax | grep searchd

shows that its already running

49630 ttys000    0:00.06 searchd --pidfile --config ../config/development.sphinx.conf
49644 ttys001    0:00.00 perl /usr/local/bin/grep searchd

and kill it

$kill -9 49630

Voila!