MYSQL EXPLAIN解析一 EXTRA中的USING INDEX，USING INDEX CONDITION
using index ：使用覆盖索引的时候就会出现
using where：在查找使用索引的情况下，需要回表去查询所需的数据
using index condition：查找使用了索引，但是需要回表查询数据
using index & using where：查找使用了索引，但是需要的数据都在索引列中能找到，所以不需要回表查询数据
查慢查询记录
# Time: 181020 11:53:11
# User@Host: zabbix[zabbix] @ localhost []
# Thread_id: 117743 Schema: zabbix QC_hit: No
# Query_time: 2.857652 Lock_time: 0.000108 Rows_sent: 576 Rows_examined: 1728
SELECT itemid,COUNT(*) AS count,AVG(value) AS avg,MIN(value) AS min,MAX(value) AS max,round(1786* MOD(CAST(clock AS UNSIGNED)+158820,172800)/(172800),0) AS i,MAX(clock) AS clock FROM history_uint WHERE itemid='59886' AND clock>='1539834780' AND clock<='1540007580' GROUP BY itemid,round(1786* MOD(CAST(clock AS UNSIGNED)+158820,172800)/(172800),0);
对zabbix的history_uint表进行优化，优化前结果是
优化后是
MariaDB [zabbix]> explain SELECT itemid,COUNT(*) AS count,AVG(value) AS avg,MIN(value) AS min,MAX(value) AS max,round(1746* MOD(CAST(clock AS UNSIGNED)+67286,86400)/(86400),0) AS i,MAX(clock) AS clock FROM history_uint WHERE itemid='42794' AND clock>='1531199914' AND clock<='1531286314' GROUP BY itemid,round(1746* MOD(CAST(clock AS UNSIGNED)+67286,86400)/(86400),0);
+------+-------------+--------------+-------+----------------+----------------+---------+------+------+--------------------------------------------------------+
| id | select_type | table | type | possible_keys | key | key_len | ref | rows | Extra |
+------+-------------+--------------+-------+----------------+----------------+---------+------+------+--------------------------------------------------------+
| 1 | SIMPLE | history_uint | range | history_uint_1 | history_uint_1 | 12 | NULL | 285 | Using index condition; Using temporary; Using filesort |
+------+-------------+--------------+-------+----------------+----------------+---------+------+------+--------------------------------------------------------+
1 row in set (0.00 sec)
MariaDB [zabbix]> explain SELECT itemid,COUNT(*) AS count,AVG(value) AS avg,MIN(value) AS min,MAX(value) AS max,round(1746* MOD(CAST(clock AS UNSIGNED)+67286,86400)/(86400),0) AS i,MAX(clock) AS clock FROM history_uint WHERE itemid='42794' AND clock>='1531199914' AND clock<='1531286314' GROUP BY itemid,round(1746* MOD(CAST(clock AS UNSIGNED)+67286,86400)/(86400),0)\G
*************************** 1. row ***************************
id: 1
select_type: SIMPLE
table: history_uint
type: range
possible_keys: history_uint_1
key: history_uint_1
key_len: 12
ref: NULL
rows: 285
Extra: Using index condition; Using temporary; Using filesort
1 row in set (0.00 sec)
MariaDB [zabbix]> show index from history_uint;
+--------------+------------+----------------+--------------+-------------+-----------+-------------+----------+--------+------+------------+---------+---------------+
| Table | Non_unique | Key_name | Seq_in_index | Column_name | Collation | Cardinality | Sub_part | Packed | Null | Index_type | Comment | Index_comment |
+--------------+------------+----------------+--------------+-------------+-----------+-------------+----------+--------+------+------------+---------+---------------+
| history_uint | 1 | history_uint_1 | 1 | itemid | A | 19 | NULL | NULL | | BTREE | | |
| history_uint | 1 | history_uint_1 | 2 | clock | A | 38955665 | NULL | NULL | | BTREE | | |
+--------------+------------+----------------+--------------+-------------+-----------+-------------+----------+--------+------+------------+---------+---------------+
2 rows in set (0.30 sec)
MariaDB [zabbix]> show columns from history_uint;
+--------+---------------------+------+-----+---------+-------+
| Field | Type | Null | Key | Default | Extra |
+--------+---------------------+------+-----+---------+-------+
| itemid | bigint(20) unsigned | NO | MUL | NULL | |
| clock | int(11) | NO | | 0 | |
| value | bigint(20) unsigned | NO | | 0 | |
| ns | int(11) | NO | | 0 | |
+--------+---------------------+------+-----+---------+-------+
4 rows in set (0.00 sec)
MariaDB [zabbix]> select count(distinct itemid),count(distinct clock),count(distinct value) from history_uint;
+------------------------+-----------------------+-----------------------+
| count(distinct itemid) | count(distinct clock) | count(distinct value) |
+------------------------+-----------------------+-----------------------+
| 10065 | 730331 | 1492694 |
+------------------------+-----------------------+-----------------------+
1 row in set (2 min 24.30 sec)
MariaDB [zabbix]> alter table history_uint add index idx_i_c_v(itemid,clock,value);
Query OK, 0 rows affected (6 min 27.53 sec)
Records: 0 Duplicates: 0 Warnings: 0
MariaDB [zabbix]> alter table history_uint drop index history_uint_1;
Query OK, 0 rows affected (0.05 sec)
Records: 0 Duplicates: 0 Warnings: 0
MariaDB [zabbix]> SHOW INDEX FROM history_uint;
+--------------+------------+-----------+--------------+-------------+-----------+-------------+----------+--------+------+------------+---------+---------------+
| Table | Non_unique | Key_name | Seq_in_index | Column_name | Collation | Cardinality | Sub_part | Packed | Null | Index_type | Comment | Index_comment |
+--------------+------------+-----------+--------------+-------------+-----------+-------------+----------+--------+------+------------+---------+---------------+
| history_uint | 1 | idx_i_c_v | 1 | itemid | A | 16 | NULL | NULL | | BTREE | | |
| history_uint | 1 | idx_i_c_v | 2 | clock | A | 33357351 | NULL | NULL | | BTREE | | |
| history_uint | 1 | idx_i_c_v | 3 | value | A | 33357351 | NULL | NULL | | BTREE | | |
+--------------+------------+-----------+--------------+-------------+-----------+-------------+----------+--------+------+------------+---------+---------------+
3 rows in set (0.09 sec)
MariaDB [zabbix]> explain SELECT itemid,COUNT(*) AS count,AVG(value) AS avg,MIN(value) AS min,MAX(value) AS max,round(1746* MOD(CAST(clock AS UNSIGNED)+67286,86400)/(86400),0) AS i,MAX(clock) AS clock FROM history_uint WHERE itemid='42794' AND clock>='1531199914' AND clock<='1531286314' GROUP BY itemid,round(1746* MOD(CAST(clock AS UNSIGNED)+67286,86400)/(86400),0)\G
*************************** 1. row ***************************
id: 1
select_type: SIMPLE
table: history_uint
type: range
possible_keys: idx_i_c_v
key: idx_i_c_v
key_len: 12
ref: NULL
rows: 284
Extra: Using where; Using index; Using temporary; Using filesort
1 row in set (0.00 sec)
MariaDB [zabbix]> explain SELECT itemid,COUNT(*) AS count,AVG(value) AS avg,MIN(value) AS min,MAX(value) AS max,round(1746* MOD(CAST(clock AS UNSIGNED)+67286,86400)/(86400),0) AS i,MAX(clock) AS clock FROM history_uint WHERE itemid='42794' AND clock>='1531199914' AND clock<='1531286314' GROUP BY itemid,round(1746* MOD(CAST(clock AS UNSIGNED)+67286,86400)/(86400),0);
+------+-------------+--------------+-------+---------------+-----------+---------+------+------+-----------------------------------------------------------+
| id | select_type | table | type | possible_keys | key | key_len | ref | rows | Extra |
+------+-------------+--------------+-------+---------------+-----------+---------+------+------+-----------------------------------------------------------+
| 1 | SIMPLE | history_uint | range | idx_i_c_v | idx_i_c_v | 12 | NULL | 284 | Using where; Using index; Using temporary; Using filesort |
+------+-------------+--------------+-------+---------------+-----------+---------+------+------+-----------------------------------------------------------+
1 row in set (0.00 sec)
MariaDB [zabbix]> select SQL_NO_CACHE itemid,COUNT(*) AS count,AVG(value) AS avg,MIN(value) AS min,MAX(value) AS max,round(1786* MOD(CAST(clock AS UNSIGNED)+158820,172800)/(172800),0) AS i,MAX(clock) AS clock FROM history WHERE itemid='59920' AND clock>='1539834780' AND clock<='1540007580' GROUP BY itemid,round(1786* MOD(CAST(clock AS UNSIGNED)+158820,172800)/(172800),0);
1785 rows in set (0.03 sec)
由原来的接近三秒优化到0.03秒
# Query_time: 101.392177 Lock_time: 0.000073 Rows_sent: 1 Rows_examined: 46443695
SET timestamp=1540089186;
select count(distinct itemid),count(distinct clock),count(distinct value) from history_uint;
MariaDB [zabbix]> select count(distinct itemid),count(distinct clock),count(distinct value) from history_uint;
+------------------------+-----------------------+-----------------------+
| count(distinct itemid) | count(distinct clock) | count(distinct value) |
+------------------------+-----------------------+-----------------------+
| 10141 | 970077 | 1697310 |
+------------------------+-----------------------+-----------------------+
1 row in set (1 min 41.39 sec)
MariaDB [zabbix]> explain select count(distinct itemid),count(distinct clock),count(distinct value) from history_uint;
+------+-------------+--------------+-------+---------------+-----------+---------+------+----------+-------------+
| id | select_type | table | type | possible_keys | key | key_len | ref | rows | Extra |
+------+-------------+--------------+-------+---------------+-----------+---------+------+----------+-------------+
| 1 | SIMPLE | history_uint | index | NULL | idx_i_c_v | 20 | NULL | 47769538 | Using index |
+------+-------------+--------------+-------+---------------+-----------+---------+------+----------+-------------+
1 row in set (0.00 sec)
MariaDB [zabbix]> select SQL_NO_CACHE count(distinct itemid),count(distinct clock),count(distinct value) from history_uint;
+------------------------+-----------------------+-----------------------+
| count(distinct itemid) | count(distinct clock) | count(distinct value) |
+------------------------+-----------------------+-----------------------+
| 10141 | 971915 | 1696308 |
+------------------------+-----------------------+-----------------------+
1 row in set (50.51 sec)
估索引前用了101秒，用了索引只要50秒