pt-index-usage
pt-index-usage：官方地址
说明
用途：从日志中(慢查询日志，查询日志)读取查询语句并分析其如何使用索引。
语法：
pt-index-usage [OPTIONS] [FILES]
主要是通过EXPLAIN来分析MySQL是如何使用索引，分析最后会给出没有使用到的索引并给出删除索引的语句，当然只针对当前的查询日志的分析结果不代表该索引就没有用，所以要人工核实后再进行相关删除操作。
具体例子
分析慢查询日志中的查询语句
[root@BigData ~]# pt-index-usage /var/lib/mysql/mysql.slow --host localhost --password 123
# A software update is available:
DBD::mysql::db do failed: Unknown database 'monitor' [for Statement "USE `monitor`"] at /bin/pt-index-usage line 6683, <> line 12550.
/var/lib/mysql/mysql.slow: 37% 00:50 remain
DBD::mysql::db selectall_arrayref failed: You have an error in your SQL syntax; check the manual that corresponds to your MariaDB server version for the right syntax to use near 'SELECT * FROM (SELECT * FROM MONITOR_IO WHERE HOST_ID=3 ORDER BY TIME DESC) A' at line 3 [for Statement "EXPLAIN SELECT * FROM MONITOR_IO WHERE HOST_ID=3 ORDER BY TIME DESC
SELECT * FROM (SELECT * FROM MONITOR_IO WHERE HOST_ID=3 ORDER BY TIME DESC) A"] at /bin/pt-index-usage line 4598, <> line 129297.
Use of uninitialized value $query in pattern match (m//) at /bin/pt-index-usage line 4591, <> line 130130.
Use of uninitialized value $query in pattern match (m//) at /bin/pt-index-usage line 4591, <> line 132062.
/var/lib/mysql/mysql.slow: 79% 00:15 remain
ALTER TABLE `dbmonitor`.`FLASH_INFO` DROP KEY `IP_IND`, DROP KEY `Time_IND`; -- type:non-unique
ALTER TABLE `dbmonitor`.`MARIADB_MONITOR_CONNECT` DROP KEY `IP_IND`, DROP KEY `TIME_IND`; -- type:non-unique
ALTER TABLE `dbmonitor`.`MARIADB_MONITOR_SINGLE` DROP KEY `IP_IND`, DROP KEY `TIME_IND`; -- type:non-unique
ALTER TABLE `dbmonitor`.`MARIADB_MS_SINGLE` DROP KEY `IP_IND`; -- type:non-unique
ALTER TABLE `dbmonitor`.`MARIADB_TRAFFIC_STATISTICS` DROP KEY `IP_IND`; -- type:non-unique
ALTER TABLE `dbmonitor`.`MEMORY` DROP KEY `ip_IND`; -- type:non-unique
ALTER TABLE `dbmonitor`.`MONITORIO` DROP KEY `IP_IND`; -- type:non-unique
ALTER TABLE `dbmonitor`.`MONITOR_DBLINK` DROP KEY `IP`; -- type:non-unique
ALTER TABLE `dbmonitor`.`SYSTEM_LOAD` DROP KEY `IP_IND`; -- type:non-unique
也可以將分析结果保存到数据库中,以后分析
pt-index-usage slow.log --no-report --save-results-database percona
会自动创建索引、查询、表和存储使用情况的相关表，表结构如下：
CREATE TABLE IF NOT EXISTS indexes (
db VARCHAR(64) NOT NULL,
tbl VARCHAR(64) NOT NULL,
idx VARCHAR(64) NOT NULL,
cnt BIGINT UNSIGNED NOT NULL DEFAULT 0,
PRIMARY KEY (db, tbl, idx)
)
CREATE TABLE IF NOT EXISTS queries (
query_id BIGINT UNSIGNED NOT NULL,
fingerprint TEXT NOT NULL,
sample TEXT NOT NULL,
PRIMARY KEY (query_id)
)
CREATE TABLE IF NOT EXISTS tables (
db VARCHAR(64) NOT NULL,
tbl VARCHAR(64) NOT NULL,
cnt BIGINT UNSIGNED NOT NULL DEFAULT 0,
PRIMARY KEY (db, tbl)
)
CREATE TABLE IF NOT EXISTS index_usage (
query_id BIGINT UNSIGNED NOT NULL,
db VARCHAR(64) NOT NULL,
tbl VARCHAR(64) NOT NULL,
idx VARCHAR(64) NOT NULL,
cnt BIGINT UNSIGNED NOT NULL DEFAULT 1,
UNIQUE INDEX (query_id, db, tbl, idx)
)
CREATE TABLE IF NOT EXISTS index_alternatives (
query_id BIGINT UNSIGNED NOT NULL, -- This query used
db VARCHAR(64) NOT NULL, -- this index, but...
tbl VARCHAR(64) NOT NULL, --
idx VARCHAR(64) NOT NULL, --
alt_idx VARCHAR(64) NOT NULL, -- was an alternative
cnt BIGINT UNSIGNED NOT NULL DEFAULT 1,
UNIQUE INDEX (query_id, db, tbl, idx, alt_idx),
INDEX (db, tbl, idx),
INDEX (db, tbl, alt_idx)
)
常用的查询语句：
1.哪些查询有时使用不同的索引，以及每个索引选择的时间比例是多少?
SELECT iu.query_id, CONCAT_WS('.', iu.db, iu.tbl, iu.idx) AS idx,
variations, iu.cnt, iu.cnt / total_cnt * 100 AS pct
FROM index_usage AS iu
INNER JOIN (
SELECT query_id, db, tbl, SUM(cnt) AS total_cnt,
COUNT(*) AS variations
FROM index_usage
GROUP BY query_id, db, tbl
HAVING COUNT(*) > 1
) AS qv USING(query_id, db, tbl);
2.哪些索引有很多备选项，即被选择而不是其他索引，以及用于哪些查询?
SELECT CONCAT_WS('.', db, tbl, idx) AS idx_chosen,
GROUP_CONCAT(DISTINCT alt_idx) AS alternatives,
GROUP_CONCAT(DISTINCT query_id) AS queries, SUM(cnt) AS cnt
FROM index_alternatives
GROUP BY db, tbl, idx
HAVING COUNT(*) > 1;
3.哪些索引被认为是其他索引的替代，以及哪些查询的替代?
SELECT CONCAT_WS('.', db, tbl, alt_idx) AS idx_considered,
GROUP_CONCAT(DISTINCT idx) AS alternative_to,
GROUP_CONCAT(DISTINCT query_id) AS queries, SUM(cnt) AS cnt
FROM index_alternatives
GROUP BY db, tbl, alt_idx
HAVING COUNT(*) > 1;
4.哪些索引时从来没有使用过的?
SELECT CONCAT_WS('.', i.db, i.tbl, i.idx) AS idx,
alt.alternative_to, alt.queries, alt.cnt
FROM indexes AS i
INNER JOIN (
SELECT db, tbl, alt_idx, GROUP_CONCAT(DISTINCT idx) AS alternative_to,
GROUP_CONCAT(DISTINCT query_id) AS queries, SUM(cnt) AS cnt
FROM index_alternatives
GROUP BY db, tbl, alt_idx
HAVING COUNT(*) > 1
) AS alt ON i.db = alt.db AND i.tbl = alt.tbl
AND i.idx = alt.alt_idx
WHERE i.cnt = 0;
5.给定一个表，有多少查询使用了哪些索引，有多少不同的指纹?有替代品吗?哪些索引没有使用?
SELECT i.idx, iu.usage_cnt, iu.usage_total,
ia.alt_cnt, ia.alt_total
FROM indexes AS i
LEFT OUTER JOIN (
SELECT db, tbl, idx, COUNT(*) AS usage_cnt,
SUM(cnt) AS usage_total, GROUP_CONCAT(query_id) AS used_by
FROM index_usage
GROUP BY db, tbl, idx
) AS iu ON i.db=iu.db AND i.tbl=iu.tbl AND i.idx = iu.idx
LEFT OUTER JOIN (
SELECT db, tbl, idx, COUNT(*) AS alt_cnt,
SUM(cnt) AS alt_total,
GROUP_CONCAT(query_id) AS alt_queries
FROM index_alternatives
GROUP BY db, tbl, idx
) AS ia ON i.db=ia.db AND i.tbl=ia.tbl AND i.idx = ia.idx;
6.给定表上的哪些索引对于至少一个查询是至关重要的(没有其他选择)?
SELECT i.db, i.tbl, i.idx, no_alt.queries
FROM indexes AS i
INNER JOIN (
SELECT iu.db, iu.tbl, iu.idx,
GROUP_CONCAT(iu.query_id) AS queries
FROM index_usage AS iu
LEFT OUTER JOIN index_alternatives AS ia
USING(db, tbl, idx)
WHERE ia.db IS NULL
GROUP BY iu.db, iu.tbl, iu.idx
) AS no_alt ON no_alt.db = i.db AND no_alt.tbl = i.tbl
AND no_alt.idx = i.idx
ORDER BY i.db, i.tbl, i.idx, no_alt.queries;
