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Notiuni avansate MySQL

Mysql
Tabele
Indecsi
Foreign key-uri
Triggere
Proceduri stocate
VIEWS
DESCRIBE
Slow query log
Query cache
Performance

Mihai Oaida <mihai.oaida@gmail.com> 01


MySQL
3.23 - vechi
4.1x - stabil, putine feature-uri
5.0x - GA
5.1 - RC
6.0x - alfa



Tabele
Tipuri de tabele
MyISAM
InnoDB
Memory / HEAP
MERGE, MRG_MyISAM
Black hole
CSV
ARCHIVE

CREATE TABLE t( columns) ENGINE =
sau
ALTER TABLE t ENGINE =



Indecsi
• Ordonam tabelul dupa 1 sau n coloane
• Tipuri de indecsi
PRIMARY KEY
Index
Unique
Full Text
• Tipuri de algoritmi : BTREE si HASH
• Aplicate pe 1 sau mai multe coloane (multiple index)

CREATE INDEX i_name ON table_name(col1,col2,..)



Full text index
Cautare in texte

SELECT id,titlu FROM table WHERE
MATCH(titlu) AGAINST(‘xml’)

SELECT id,titlu FROM table WHERE
MATCH(titlu) AGAINST(‘xml’ WITH QUERY
EXPANSION)



Foreign key
Creeaza legaturile intre tabele care la proiectare
le creem prin conventie. Ex : news.cat_id – cat.id

Ex : InnoDB
Se poate pune la create tabele sau ulterior

FOREIGN KEY(cat_id) REFERENCES cat(id)



Triggere
Obiect asociat unui tabel care se apeleaza la un
anumit eveniment
CREATE TRIGGER trig_name {BEFORE| AFTER}
{INSERT,REPLACE,UPDATE, DELETE} on t
FOR EACH ROW BEGIN
..sql..
END;



Exemplu

CREATE TRIGGER updateCateg AFTER INSERT ON
produse
FOR EACH ROW BEGIN
UPDATE cats SET nr=nr+1 WHERE
id=NEW.cat_id;
END;



Proceduri stocate
Subrutine care se retin in baza de date

Folosite pentru
A testa datele
A muta sql din logica aplicatiei in db
A minimiza traficul dintre client si db



Exemplu
delimiter //
DROP PROCEDURE IF EXISTS colavg//
CREATE PROCEDURE colavg(IN tbl CHAR(64),IN col
CHAR(64))

READS SQL DATA
COMMENT 'Selects the avg of column col in table tbl'
BEGIN SET @s = CONCAT('SELECT AVG(' , col , ') FROM
' , tbl);
PREPARE stmt FROM @s;
EXECUTE stmt;
END;
//
delimiter ;

CALL colavg(‘t_note’,’nota’);



VIEWS
CREATE VIEW view_name AS [query]
DROP VIEW view_name
CREATE VIEW stats_l AS SELECT l.id,l.nume, ( SELECT
count( c.id ) FROM comentarii c WHERE c.lectie_id
= l.id ) AS nr_comentarii , ( SELECT count( r.id
) FROM rezolvari r WHERE r.lectie_id = l.id ) AS
nr_rezolvari FROM lectii l ORDER BY id ASC

SELECT * FROM stats_l



DESCRIBE
• Arata planul de executie ales de optimizator
• Arata pentru fiecare tabel din sql : indecsi
folositi,tipul cautarii, nr de randuri prin care
cauta,etc
• DESCRIBE [sql]
• Campuri
Select_type – tip qurery
Table – nume tabel
Possible_keys – key-uri luate in considerare
Key – cheia aleasa
Key_len - lungimea
Rows – numar aprox row-uri prin care cauta
Extra – file sort, tmp table, etc


Slow query log
Location my.ini
log_slow_queries = /var/log/mysql/my-slow.log
long_query_time = 2
log-queries-not-using-indexes



Query cache
Location my.ini
query_cache_limit = 64M
query_cache_size = 64M

Nu trebuie setata prea mare

Raportul read/write – invalidarea cache-ului

Trebuie urmarit cache hits



Performanta
• Datele retinute pe tipul cel mai mic
md5 hash – binary(16) pack()
ip – int 4 bytes ip2long()

• Indecsi mici – mai multa informatie incape
intr-un bloc de memorie

• Indecsi pe cheia de join
• Binary log off

Don’t
SELECT * FROM table ORDER BY RAND() LIMIT 1
SELECT COUNT(*) FROM table
SELECT DISTINCT column FROM table


Referinte
RTFM
http://dev.mysql.com/doc/refman/5.0/en/
http://dev.mysql.com/tech-resources/articles/

Scule
http://dev.mysql.com/workbench/
http://dev.mysql.com/downloads/gui-tools/5.0.html
http://munin.projects.linpro.no/

Lectura
http://www.mysqlperformanceblog.com/



Intrebari?

Mihai Oaida <mihai.oaida@gmail.com>

Advanced Mysql - GeekMeet Timisoara

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