Question

I’ve run into a problem where I run some query and the mysqld process starts using 100% CPU power, without ending. I want to pinpoint this query. The problem is that log/development.log contains only queries that have finished. Any idea?

Answer 1

If you have assess to MySQL, consider the SQL query

SHOW PROCESSLIST 

Or from the command line:

mysqladmin processlist 

Alternatively, the most powerful way is to override the ‘execute’ method of the ActiveRecord::Base connection instance. This article shows the general approach:

http://www.misuse.org/science/2006/12/12/sql-logging-in-rails/

You put this code into application.rb:

# define SQL_LOG_FILE, SQL_LOG_MAX_LINES  connection = ActiveRecord::Base.connection class << connection     alias :original_exec :execute     def execute(sql, *name)         # try to log sql command but ignore any errors that occur in this block         # we log before executing, in case the execution raises an error         begin             lines = if File::exists?(SQL_LOG_FILE) then IO::readlines(SQL_LOG_FILE) else [] end             log = File.new(SQL_LOG_FILE, 'w+')             # keep the log to specified max lines             if lines.length > SQL_LOG_MAX_LINES                 lines.slice!(0..(lines.length-SQL_LOG_MAX_LINES))             end             lines << Time.now.strftime('%x %I:%M:%S %p')+': '+sql+'n'             log.write(lines)             log.close             $sql_log = sql         rescue Exception => e             ;         end         # execute original statement         original_exec(sql, *name)     end # def execute end # class <<