Re: Using fprintf or DBUG_PRINT to print messages in mysqld

On 9/5/2011 3:43 AM, Salil Bhagurkar wrote:
> Hello All,
>
> I am trying to understand the code flow of mysql-5.5.15 mysqld server.
>
> 1. I am able to use fprintf(stdout, ..) to print out messages to the
> console in the main startup code of mysqld.
>
> 2. I cannot use fprintf in any of the thread context to print messages
> to the console. Why is this?
>
	The MySQL logging system redirects both stdout and stderr to the MySQL 
log file. use tail -f /var/log/mysql.log to see your messages.

> 3. If I compile the source code with the debug option and use
> DBUG_PRINT, then it does not work in some cases, specifically in the
> function do_handle_one_connection() in sql/sql_connect.cc.
>
> 4. DBUG_PRINT works and is used in the function do_command which is
> called by the do_handle_one_connection() method. From what I observed,
> is DBUG_ENTER always required to be able to DBUG_PRINT?
>
	Yes, and DEBUG_RETURN() or DBUG_VOID_RETURN; These are macros, each of 
which sets (or clears) some global state. They must be used together.

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