带有子查询的mysql基础上的删除速度非常慢

Very slow delete on mysql base with subquery(带有子查询的mysql基础上的删除速度非常慢)

问题描述

这个 mysql 查询运行了大约 10 个小时，还没有完成.出事了.

This mysql query is running for around 10 hours and has not finished. Something is horribly wrong.

这里有两个表格(文本和垃圾邮件).Spam 将垃圾邮件条目的 ID 存储在我要删除的文本中.

Two tables (text and spam) are here. Spam stores the ids of spam entrys in text that I want to delete.

DELETE FROM tname.text WHERE old_id IN (SELECT textid FROM spam);

spam 只有 2 列，都是整数.800K 条目的文件大小为几 Mbs.两个整数都是主键.

spam has just 2 columns, both are ints. 800K entries has a file size of several Mbs. Both ints are primary keys.

文本有 3 列.id(主键)、文本、标志.大约 1200K 条目和大约 2.1 GB 大小(大多数垃圾邮件).

text has 3 columns. id (prim key), text, flags. around 1200K entries, and around 2.1 gigabyte size (most spam).

服务器是一个至强四核，2 GB 内存(不要问我为什么).只有 apache(为什么?)和 mysqld 正在运行.它是一个旧的免费 bsd 和 mysql 4.1.2(不要问我为什么)

The server is a xeon quad, 2 gigabyte ram (don't ask me why). Only apache (why?) and mysqld is running. Its an old free bsd and mysql 4.1.2 (don't ask me why)

线程:6 问题:188805 慢查询:318 打开:810 刷新表:1 打开表:157 每秒查询平均:7.532

Threads: 6 Questions: 188805 Slow queries: 318 Opens: 810 Flush tables: 1 Open tables: 157 Queries per second avg: 7.532

Mysql my.cnf:

Mysql my.cnf:

[mysqld]
datadir=/usr/local/mysql
log-error=/usr/local/mysql/mysqld.err
pid-file=/usr/local/mysql/mysqld.pid
tmpdir=/var/tmp
innodb_data_home_dir =
innodb_log_files_in_group = 2
join_buffer_size=2M
key_buffer_size=32M
max_allowed_packet=1M
max_connections=800
myisam_sort_buffer_size=32M
query_cache_size=8M
read_buffer_size=2M
sort_buffer_size=2M
table_cache=256
skip-bdb
log-slow-queries = slow.log
long_query_time = 1

#skip-innodb
#default-table-type=innodb
innodb_data_file_path = /usr/local/mysql/ibdata1:10M:autoextend
innodb_log_group_home_dir = /usr/local/mysql/
innodb_buffer_pool_size = 128M
innodb_log_file_size = 16M
innodb_log_buffer_size = 8M
#innodb_flush_log_at_trx_commit=1
#innodb_additional_mem_pool_size=1M
#innodb_lock_wait_timeout=50

log-bin
server-id=201

[isamchk]
key_buffer_size=128M
read_buffer_size=128M
write_buffer_size=128M
sort_buffer_size=128M

[myisamchk]
key_buffer_size=128M[server:~] dmesg | grep memory
real memory  = 2146828288 (2047 MB)
avail memory = 2095534080 (1998 MB)

read_buffer_size=128M
write_buffer_size=128M
sort_buffer_size=128M
tmpdir=/var/tmp

查询只使用一个 cpu，top 表示 25% cpu 时间(所以 1 of 4).

The query is using just one cpu, top says 25% cpu time (so 1 of 4).

real memory  = 2146828288 (2047 MB)
avail memory = 2095534080 (1998 MB)

62 processes:  2 running, 60 sleeping
CPU states: 25.2% user,  0.0% nice,  1.6% system,  0.0% interrupt, 73.2% idle
Mem: 244M Active, 1430M Inact, 221M Wired, 75M Cache, 112M Buf, 31M Free
Swap: 4096M Total, 1996K Used, 4094M Free

  PID USERNAME     THR PRI NICE   SIZE    RES STATE  C   TIME   WCPU COMMAND
11536 mysql         27  20    0   239M   224M kserel 3 441:16 94.29% mysqld

知道怎么解决吗?

推荐答案

根据我的经验，子查询通常是 SQL 语句执行时间缓慢的原因，因此我尽量避免它们.试试这个:

In my experience sub queries are often a cause of slow execution times in SQL statements, therefor I try to avoid them. Try this:

DELETE tname FROM tname INNER JOIN spam ON (tname.old_id = spam.textid);

免责声明:此查询未经测试，请先备份！:-)

Disclaimer: This query is not tested, make backups first! :-)

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