mysql慢日志问题排查
1.下载慢日志文件
show variables like '%query%';
| 变量 | 值 |
|---|---|
| long_query_time | 0.100000（执行时间超过0.1秒的会记录到慢日志文件） |
| slow_query_log | ON （表明慢查询日志打开） |
| slow_query_log_file | /export/data/mysql/log/slow.log（慢日志文件路径） |
可以根据slow_query_log_file的值来下载慢日志文件
2.使用mysqldumpslow分析慢日志文件
mysqldumpslow slow.log
结果默认按照单个语句最长执行时间倒序排序，类似这样：
Count: 47 Time=5.09s (239s) Lock=0.00s (0s) Rows=38.0 (1786), regular_purch_rw[regular_purch_rw]@3hosts
select
t.id, t.plan_id, t.pre_period_id, t.order_id, t.period_num, t.price, t.coupon_price, t.pay_mode, t.receive_id, t.regular_discount,
t.distribute_time, t.status, t.sub_status, t.created, t.modified,t.freight, t.coupon_id, t.coupon_batch_key, t.order_time, t.isupdatepromise, t.wright_pushed
from
regular_purchase_plan_period_info as t
where
order_id is NULL
and sub_status in (N,N)
and status = N
and pay_mode = N
and distribute_time between 'S' and 'S'
and wright_pushed != N
Count: 46 Time=4.35s (199s) Lock=0.00s (0s) Rows=0.0 (0), regular_purch_rw[regular_purch_rw]@4hosts
select
id, plan_id, father_order_id, period_num, price, coupon_id, coupon_price, regular_discount,
freight, distribute_time, pay_mode, business_type, status, sub_status, order_time,
is_update_promise, wright_pushed, pin, name, province_code, city_code, county_code,
town_code, province_name, city_name, county_name, town_name, address, mobile, ext_map,
yn, created, modified
from
plan_detail
where
sub_status in (N,N)
and status = N
and pay_mode = N
and distribute_time between 'S' and 'S'
and wright_pushed != N
and yn = N
count:执行次数
time：执行最长时间（累计耗费总时长）
lock：等待锁的时间
rows：发送给客户端的行总数(扫描的行总数),
用户
抽象sql语句
下面介绍一下mysqldumpslow的详细用法
mysqldumpslow --help
Usage: mysqldumpslow [ OPTS... ] [ LOGS... ]
Parse and summarize the MySQL slow query log. Options are
--verbose verbose
--debug debug
--help write this text to standard output
-v verbose
-d debug
-s ORDER what to sort by (al, at, ar, c, l, r, t), 'at' is default
al: average lock time
ar: average rows sent
at: average query time
c: count
l: lock time
r: rows sent
t: query time
-r reverse the sort order (largest last instead of first)
-t NUM just show the top n queries
-a don't abstract all numbers to N and strings to 'S'
-n NUM abstract numbers with at least n digits within names
-g PATTERN grep: only consider stmts that include this string
-h HOSTNAME hostname of db server for *-slow.log filename (can be wildcard),
default is '*', i.e. match all
-i NAME name of server instance (if using mysql.server startup script)
-l don't subtract lock time from total time
mysqldumpslow可以按照不同的方式排序，使用-s选项；
可以只列出topn的sql，使用-t选项
3. 逐个sql语句分析
根据mysqldumpslow给出的信息，可以进行单个sql针对性的分析。
- 单次执行过长，可以使用explain进行分析，看是否使用索引，是都使用合适的索引。
- 执行次数过多，可以考虑减少重复执行，减轻单台机器压力（读写分离，读走从库之类的操作）。
- 锁持有时间过长，看是否有长事务，是否事务没有提交，是否锁竞争激烈，是否有死锁，是否加锁顺序不合理
- 扫描行数过多，还是看索引。
- 返回用户行数过多，看是否能将sql拆分，返回合理的行数。