Do you use MySQL replication? Do you use “FLUSH LOGS”? If yes you might want to read this.

Posted: 31st August 2010 by Darren Cassar in Intermediate, MySQL
Tags: , , , ,
4

Scenario: Master-Master replication
Description: Master A is the active db server whilst Master B is a read only swappable db server hence both are creating binary logs. During backup I run “FLUSH LOGS” in order to have a simpler point in time recovery procedure if that case arises.
Problem: Flush logs is mean mean command :) …. it rotates not only my binary logs but my error log too (since I user error-log=blahblahblah in my my.cnf). Well given I flush logs every night my error log is cycled through every night, but unlike binary logs which have an incrimental number attached to the fine, error logs only have a `-log` attached to the filename and a second “FLUSH LOG” would just clear all error logs permanently. That is really not fun believe me!

So what is the solution? you could either:
1. Not use “FLUSH LOGS” (nah that aint happenin)
2. Not use –error-log (that aint happenin either cos I need to use it for my specific setup)
3. Create an ugly hack script which saves the error log or renames it or whatever (Ugly Ugly)
4. Create a variable in MySQL which says: flush-log-ignore-error-log which if set “FLUSH LOGS” will know not to mess around with my error log. Hence … create a feature request (nicer and friendlier solution) and submit a tested patch too whilst at it.

If you think it is not idea that “FLUSH LOGS” recycles through error logs or and you have been bitten by the way it works like me, then feel free to put your vote into http://bugs.mysql.com/bug.php?id=56385&thanks=sub so that MySQL sees the importance of it.

Because Sharing is Caring!

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Getting a return code from a stored procedure

Posted: 26th August 2010 by Darren Cassar in Intermediate, MySQL, Uncategorized
Tags: , ,
0

Sometimes we have some special need for a stored procedure to call another to do something. That is fine, but what if the second stored proc failed for some reason? Maybe you want to halt the first stored procedure (the caller) and not proceed with the work until the problem is verified and resolved. So How do you do it?

Simple, get a return code from the called procedure to determine if it worked or not!

Here’s a sample piece of code to explain better:


DROP PROCEDURE IF EXISTS `test`.`testing123`;
DELIMITER $$

CREATE
PROCEDURE `test`.`testing123`(OUT a INT)
BEGIN
DECLARE EXIT HANDLER FOR SQLEXCEPTION
BEGIN
SET a=2;
END;
SET a=0;

# toggle the below as comment or not to see the call at the bottom working
# if you uncomment select abc you'll see the error, otherwise all is cool

# select abc;

END$$

DELIMITER ;

DROP PROCEDURE IF EXISTS `test`.`testing456`;
DELIMITER $$

CREATE
PROCEDURE `test`.`testing456`()
BEGIN
SET @a=0;
CALL `test`.`testing123` (@a);

IF @a != 0 THEN
SELECT "There is a problem with proc `testing123`";
ELSE
SELECT "Everything is cool";
END IF;

END$$

DELIMITER ;

CALL `test`.`testing456` ();

testing123 is the second stored proc in this case, called from testing456. The trick is to have an exit handler which returns a status number to the first stored proc (testing456). The latter will hold an if condition to do `something` depending on the return code received by testing123.

If you have any other suggestions I’d appreciate your input.

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MySQL stored procedure debugging, can I sue for going insane?

Posted: 23rd August 2010 by Darren Cassar in Advanced, MySQL
Tags: , , , ,
4

Lets paint the picture:

Scenario part 1 : Migrating a couple thousand stored procedures from database technology X to mysql
Scenario part 2 : Legacy system where the people who wrote it left a long time ago
Scenario part 3 : Developers sure can get real creative and invent all kinds of ways to get data (eg: having a stored proc which formulates a big query using concat after going through a bunch of conditions (fair enough), BUT the parts making up the different queries are stored in a table on a database rather than within the stored proc itself) … talk about KIS – Keep it simple!!
Scenario part 4 : This stored proc references 18 tables, 4 views, and another two stored procedures on 5 databases

Now close your eyes and try to imagine that for a few seconds, nah kidding don’t want you to hurt yourself.

I wonder, who’s gonna cover my health insurance if i go crazy? :)

mysql 02:55:47 DEV > call storedprocblahbla(‘I’,'am’,'going’,'crazy’);
ERROR 1052 (23000): Column ‘state_of_mind’ in field list is ambiguous

Sure thats REALLY REALLY helpful thanks :), you know what, lets just mysqldump -d -R -B db1 db2 db3 db4 db5 > /wherever/you/like and grep for column ‘state_of_mind’.

I love a challenge but facing migration of so many stored procs I’d really love to have something “GOOD” to debug them with.

The solutions I found were:
1. Illatis eclipse plugin for $40
works on linux, mac and windows but does show me a lot of:
“An error has occurred when activating this view
com/illatis/parser/lib/k”
2. mydebugger for $50
works on linux and mac via wine
3. dbForge for MySQL for $50
works only on windows due to .net framework (kinda crap because I `hate` using the former)

any other ideas are very welcome, especially opensource ones but I can’t find anything.

I can always try setting up debugging using GDB but would rather try to avoid that.

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