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MySQL优化 之 Discuz论坛优化
MySQL高级技术
周四, 2006/12/21 - 13:50
作/译者：叶金荣（Email:），来源：http://imysql.cn，转载请注明作/译者和出处，并且不能用于商业用途，违者必究。
一. 前言
近日由于需要,对discuz论坛(简称dz)进行优化,当然了,只是涉及到数据库的优化.
先说一下服务器及dz的数据量,2 * Intel(R) Xeon(TM) CPU 2.40GHz, 4GB mem, SCISC硬盘.
MySQL 版本为 4.0.23. 数据表情况:
cdb_attachments 2万
cdb_members 10万
cdb_posts 68万
cdb_threads 7万
二. 缓存优化
在 my.cnf 中添加/修改以下选项:
#取消文件系统的外部锁skip-locking#不进行域名反解析,注意由此带来的权限/授权问题skip-name-resolve#索引缓存,根据内存大小而定,如果是独立的db服务器,可以设置高达80%的内存总量key_buffer = 512M#连接排队列表总数back_log = 200max_allowed_packet = 2M#打开表缓存总数,可以避免频繁的打开数据表产生的开销table_cache = 512#每个线程排序所需的缓冲sort_buffer_size = 4M#每个线程读取索引所需的缓冲read_buffer_size = 4M#MyISAM表发生变化时重新排序所需的缓冲myisam_sort_buffer_size = 64M#缓存可重用的线程数thread_cache = 128#查询结果缓存query_cache_size = 128M#设置超时时间,能避免长连接set-variable = wait_timeout=60#最大并发线程数,cpu数量*2thread_concurrency = 4#记录慢查询,然后对慢查询一一优化log-slow-queries = slow.loglong_query_time = 1#关闭不需要的表类型,如果你需要,就不要加上这个skip-innodbskip-bdb
以上参数根据各自服务器的配置差异进行调整,仅作为参考.
三. 索引优化
上面提到了,已经开启了慢查询,那么接下来就要对慢查询进行逐个优化了.
1. 搜索优化
搜索的查询SQL大致如下:
SELECT t.* FROM cdb_posts p, cdb_threads t WHEREt.fid IN (‘37‘, ‘45‘, ‘4‘, ‘6‘, ‘17‘, ‘41‘, ‘28‘, ‘32‘, ‘31‘, ‘1‘, ‘42‘)AND p.tid=t.tid AND p.author LIKE ‘JoansWin‘GROUP BY t.tid ORDER BY lastpost DESC LIMIT 0, 80;
用 EXPLAIN 分析的结果如下:
mysql>EXPLAIN SELECT t.* FROM cdb_posts p, cdb_threads t WHEREt.fid IN (‘37‘, ‘45‘, ‘4‘, ‘6‘, ‘17‘, ‘41‘, ‘28‘, ‘32‘, ‘31‘, ‘1‘, ‘42‘)AND p.tid=t.tid AND p.author LIKE ‘JoansWin‘GROUP BY t.tid ORDER BY lastpost DESC LIMIT 0, 80;+-----------+------------+----------+--------------+-------------+-----------+-------------+| id | select_type | table | type | possible_keys | key | key_len | ref | rows | Extra+-----------+------------+----------+--------------+-------------+-----------+-------------+| 1 | SIMPLE | t | range | PRIMARY,fid | fid | 2 | NULL | 66160 | Using where;Using temporary; Using filesort || 1 | SIMPLE | p | ref | tid | tid | 3 | Forum.t.tid | 10 | Using where| +----+-------------+-------+-------+---------------+------+---------+-------------+-------+---------
只用到了 t.fid 和 p.tid,而 p.author 则没有索引可用,总共需要扫描
66160*10 = 661600 次索引,够夸张吧 :(
再分析 cdb_threads 和 cdb_posts 的索引情况:
mysql>show index from cdb_posts;+-----------+------------+----------+--------------+-------------+-----------+-------------+----------+--------+------+--+| Table | Non_unique | Key_name | Seq_in_index | Column_name | Collation | Cardinality | Sub_part |Packed | Null | Index_type | Comment | +-----------+------------+----------+--------------+-------------+-----------+-------------+----------+--------+------+--+| cdb_posts | 0 | PRIMARY | 1 | pid | A | 680114 | NULL | NULL || BTREE | || cdb_posts | 1 | fid | 1 | fid | A | 10 | NULL | NULL || BTREE | || cdb_posts | 1 | tid | 1 | tid | A | 68011 | NULL | NULL || BTREE | || cdb_posts | 1 | tid | 2 | dateline | A | 680114 | NULL | NULL || BTREE | || cdb_posts | 1 | dateline | 1 | dateline | A | 680114 | NULL | NULL || BTREE | |+-----------+------------+----------+--------------+-------------+-----------+---
以及
mysql>show index from cdb_threads;+-----------+------------+----------+--------------+-------------+-----------+-------------+----------+--------+------+-----+| Table | Non_unique | Key_name | Seq_in_index | Column_name | Collation | Cardinality | Sub_part |Packed | Null | Index_type | Comment | +-----------+------------+----------+--------------+-------------+-----------+-------------+----------+--------+------+-----+| cdb_threads | 0 | PRIMARY | 1 | tid | A | 68480 | NULL | NULL || BTREE | || cdb_threads | 1 | lastpost | 1 | topped | A | 4 | NULL | NULL || BTREE | || cdb_threads | 1 | lastpost | 2 | lastpost | A | 68480 | NULL | NULL || BTREE | || cdb_threads | 1 | lastpost | 3 | fid | A | 68480 | NULL | NULL || BTREE | || cdb_threads | 1 | replies | 1 | replies | A | 233 | NULL | NULL || BTREE | || cdb_threads | 1 | dateline | 1 | dateline | A | 68480 | NULL | NULL || BTREE | || cdb_threads | 1 | fid | 1 | fid | A | 10 | NULL | NULL || BTREE | || cdb_threads | 1 | enablehot | 1 | enablehot | A | 2 | NULL | NULL || BTREE | | +-------------+------------+-----------+--------------+-------------+------
看到索引 fid 和 enablehot 基数太小,看来该索引完全没必要,不过,对于fid基数较大的情况,则可能需要保留>该索引.
所做修改如下:
ALTER TABLE `cdb_threads` DROP INDEX `enablehot`, DROP INDEX `fid`, ADD INDEX (`fid`, `lastpost`);ALTER TABLE `cdb_posts` DROP INDEX `fid`, ADD INDEX (`author`(10));OPTIMIZE TABLE `cdb_posts`;OPTIMIZE TABLE `cdb_threads`;
在这里, p.author 字段我设定的部分索引长度是 10, 是我经过分析后得出来的结果,不同的系统,这里的长度也不同,最好自己先取一下平均值,然后再适当调整.
现在,再来执行一次上面的慢查询,发现时间已经从 6s 变成 0.19s,提高了 30 倍.
这次先到这里,下次继续 ^_^