High Performance MySQL Optimization, Backups, Replication, and More (Paperback)
Myterm: Extensible mysql command line client with pipe chaining
“Tail -f table with myterm” Ever found yourself running the same query over and over again to see if a table has got new content, just waiting for that magic row to appear? The tail command will watch for new lines in a table, just like you might tail a log file in Linux.
The easiest way to generate random rows in MySQL is to use the ORDER BY RAND() clause. This can work fine for small tables. However, for big tables, it will have a serious performance problem, as in order to generate the list of random rows, MySQL needs to assign random number to each row and then sort them.
mysql> create database db_name ; mysql> CREATE USER 'user'@'%' IDENTIFIED BY 'secret'; mysql> grant all privileges on db_name.* to user@'%' ;
A user for backup only :
CREATE USER 'backup'@'localhost' IDENTIFIED BY 'password'; REVOKE ALL PRIVILEGES ON *.* FROM 'backup'@'localhost'; REVOKE GRANT OPTION ON *.* FROM 'backup'@'localhost'; GRANT SELECT, LOCK TABLES ON *.* TO 'backup'@'localhost' WITH MAX_QUERIES_PER_HOUR 0 MAX_CONNECTIONS_PER_HOUR 0 MAX_UPDATES_PER_HOUR 0 MAX_USER_CONNECTIONS 0 ; FLUSH PRIVILEGES;
$ service mysql stop $ mysqld_safe --skip-grant-tables
dans un autre terminal:
$ mysql -u root UPDATE mysql.user SET Password=PASSWORD('TheNewPassword') WHERE User='root'; exit
tuer le “mysqld_safe” avec un Ctrl^C
$ service mysql start
Dans le corps d'un Trigger ou d'une Stored Procedure il peut y avoir des ';', alors il faut un nouveau séparateur pour délimiter l'ensemble. C'est DELIMITER :
DELIMITER //
CREATE TRIGGER t_bu BEFORE UPDATE ON t FOR EACH ROW BEGIN DECLARE CONTINUE HANDLER FOR 1264 SET new.column1 = -1; SET new.column1 = new.column1 * 2; END;//
http://dev.mysql.com/doc/refman/5.1/en/create-trigger.html
Quelques exemples :
CREATE TRIGGER trigger_name trigger_time trigger_event ON tbl_name FOR EACH ROW trigger_stmt
wa_Guide, un nouveau tuple doit être insérer dans wa_GuideVote (table gérant les votes des visiteurs au niveau de chaque guide) avec comme idGuide l’id du guide qui a été ajouté. Avec un trigger cela donne ceci :
CREATE TRIGGER voteGuideInsert AFTER INSERT ON wa_Guide FOR EACH ROW INSERT INTO wa_GuideVote (idGuide) VALUES (NEW.idGuide);
Vous allez me dire que si on supprime un guide il va rester un tuple inutile dans wa_GuideVote. Et bien non ! :
CREATE TRIGGER voteGuideDelete AFTER DELETE ON wa_Guide FOR EACH ROW DELETE FROM wa_GuideVote WHERE idGuide = OLD.idGuide;
Un astuce pour gérer un cache de données: quand une table est mise à jour elle met à jour un timestamp dans une autre table. ceci permet de tenir des valeurs de last modification par groupe de données.
DROP TRIGGER IF EXISTS TABLE_A1_TRIGGER ; CREATE TRIGGER TABLE_A1_TRIGGER AFTER INSERT ON TABLE_A1 FOR each ROW REPLACE INTO LAST_MOD (lm_module) VALUES ('MyModule')
Et encore d'autres :
delimiter // CREATE TRIGGER survey_check_empty BEFORE INSERT ON surv_surveys FOR EACH ROW BEGIN IF LENGTH(NEW.survey_name) <1 THEN RETURN FALSE; END IF; END; // delimiter ;
delimiter // DROP TRIGGER demande_before_insert// CREATE TRIGGER demande_before_insert BEFORE INSERT ON demande FOR EACH ROW BEGIN DECLARE i_decalage NUMERIC; DECLARE c_file_demandes CURSOR FOR SELECT decalage_sec FROM file_demandes, themes WHERE file_demandes.id_theme = themes.id AND file_demandes.id = NEW.id_file_demandes; # valorise la DATE cible si elle est vide IF(NEW.date_objectif='0000-00-00 00:00:00' OR NEW.date_objectif IS NULL)THEN OPEN c_file_demandes; FETCH c_file_demandes INTO i_decalage; CLOSE c_file_demandes; SET NEW.date_objectif = DATE_ADD(NEW.timestamp, INTERVAL i_decalage SECOND); END IF; END;// delimiter ;
UPDATE a_table SET content = REGEXP_REPLACE(content, '##', '$$') WHERE content LIKE '%##%'
Attention, il faut 2 anti-slash pour le ?
. Exemple pour supprimer le spam WordPress weatherplllatform
:
UPDATE wpci_posts SET post_content = REGEXP_REPLACE( post_content , "<script src='https://new\.weatherplllatform\.com/pick\.js\\?v=11\.87\.33' type='text/javascript'></script>", '' ) WHERE post_content LIKE "%weatherplllatform%"
Articles:
auto_increment_increment
and auto_increment_offset
variables such that one only uses odd numbers for auto-incrementing integer primary keys and the other use even bumbersSans arrêter le Master avec l'option “–master-data” de mysqldump.
Dans /var/log/syslog
des lignes comme …mysqld[123]: 101015 21:11:19 [ERROR] Slave: Error…
Optimisation.