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Comparative analysis of the execution efficiency of MySQL 5.7 statistical table records
2022-07-06 12:48:00 【wx5caecf2ed0645】
Problem description
When the statistics are recorded , I seldom pay attention to the details , I have time to analyze it for a few days , Here is my analysis process , What's wrong , Also please correct me .
[email protected]#mysql.sock : tc0112:28:09>select count(*) from test2;
+----------+
| count(*) |
+----------+
| 1120198 |
+----------+
1 row in set (0.13 sec)
[email protected]#mysql.sock : tc0112:28:11>select count(*) from test2;
+----------+
| count(*) |
+----------+
| 1120198 |
+----------+
1 row in set (0.13 sec)
[email protected]#mysql.sock : tc0112:28:13>select count(*) from test2;
+----------+
| count(*) |
+----------+
| 1120198 |
+----------+
1 row in set (0.13 sec)
[email protected]#mysql.sock : tc0112:28:14>
It has been queried three times, and the time consumption of each query is 0.13 second .
[email protected]#mysql.sock : tc0112:31:01>select count(*) from test2 use index (PRIMARY);
+----------+
| count(*) |
+----------+
| 1120198 |
+----------+
1 row in set (0.15 sec)
[email protected]#mysql.sock : tc0112:31:02>select count(*) from test2 use index (PRIMARY);
+----------+
| count(*) |
+----------+
| 1120198 |
+----------+
1 row in set (0.15 sec)
[email protected]#mysql.sock : tc0112:31:05>select count(*) from test2 use index (PRIMARY);
+----------+
| count(*) |
+----------+
| 1120198 |
+----------+
1 row in set (0.15 sec)
Used the primary key to query three times , Each query takes 0.15 second , Why there will be 0.02 What about the difference in seconds ？
The analysis process
View execution plan
Our first thought is to see if the implementation plan is the same .
[email protected]#mysql.sock : tc0112:33:34>explain select count(*) from test2;
+----+-------------+-------+------------+-------+---------------+----------------+---------+------+---------+----------+-------------+
| id | select_type | table | partitions | type | possible_keys | key | key_len | ref | rows | filtered | Extra |
+----+-------------+-------+------------+-------+---------------+----------------+---------+------+---------+----------+-------------+
| 1 | SIMPLE | test2 | NULL | index | NULL | index_vote_num | 4 | NULL | 1114117 | 100.00 | Using index |
+----+-------------+-------+------------+-------+---------------+----------------+---------+------+---------+----------+-------------+
1 row in set, 1 warning (0.07 sec)
[email protected]#mysql.sock : tc0112:33:35>explain select count(*) from test2 use index (PRIMARY);
+----+-------------+-------+------------+-------+---------------+---------+---------+------+---------+----------+-------------+
| id | select_type | table | partitions | type | possible_keys | key | key_len | ref | rows | filtered | Extra |
+----+-------------+-------+------------+-------+---------------+---------+---------+------+---------+----------+-------------+
| 1 | SIMPLE | test2 | NULL | index | NULL | PRIMARY | 4 | NULL | 1114117 | 100.00 | Using index |
+----+-------------+-------+------------+-------+---------------+---------+---------+------+---------+----------+-------------+
1 row in set, 1 warning (0.00 sec)
From the execution plan shown, we can see that , Two SQL The execution plan of the statement is different , The primary key index is slow 0.02 second , What's the cause of the ？
Check the index as follows ：
[email protected]#mysql.sock : tc0112:34:27>show index from test2;
+-------+------------+----------------+--------------+-------------+-----------+-------------+----------+--------+------+------------+---------+---------------+
| Table | Non_unique | Key_name | Seq_in_index | Column_name | Collation | Cardinality | Sub_part | Packed | Null | Index_type | Comment | Index_comment |
+-------+------------+----------------+--------------+-------------+-----------+-------------+----------+--------+------+------------+---------+---------------+
| test2 | 0 | PRIMARY | 1 | id | A | 1054391 | NULL | NULL | | BTREE | | |
| test2 | 1 | index_name | 1 | name | A | 1055674 | NULL | NULL | | BTREE | | |
| test2 | 1 | index_vote_num | 1 | vote_num | A | 9929 | NULL | NULL | | BTREE | | |
| test2 | 1 | index_group | 1 | group_id | A | 501 | NULL | NULL | | BTREE | | |
| test2 | 1 | index_group | 2 | sdate | A | 824214 | NULL | NULL | YES | BTREE | | |
+-------+------------+----------------+--------------+-------------+-----------+-------------+----------+--------+------+------------+---------+---------------+
5 rows in set (0.00 sec)
cardinality Is the estimate of non duplicate records in the index .
Use profile See where the time difference lies
[email protected]#mysql.sock : tc0112:41:21>select count(*) from test2;
+----------+
| count(*) |
+----------+
| 1120198 |
+----------+
1 row in set (0.14 sec)
[email protected]#mysql.sock : tc0112:41:33>show profile cpu,block io for query 3;
+----------------------+----------+----------+------------+--------------+---------------+
| Status | Duration | CPU_user | CPU_system | Block_ops_in | Block_ops_out |
+----------------------+----------+----------+------------+--------------+---------------+
| starting | 0.000047 | 0.000033 | 0.000009 | 0 | 0 |
| checking permissions | 0.000005 | 0.000004 | 0.000001 | 0 | 0 |
| Opening tables | 0.000013 | 0.000010 | 0.000003 | 0 | 0 |
| init | 0.000011 | 0.000008 | 0.000003 | 0 | 0 |
| System lock | 0.000006 | 0.000005 | 0.000001 | 0 | 0 |
| optimizing | 0.000003 | 0.000003 | 0.000001 | 0 | 0 |
| statistics | 0.000010 | 0.000007 | 0.000002 | 0 | 0 |
| preparing | 0.000007 | 0.000006 | 0.000002 | 0 | 0 |
| executing | 0.000002 | 0.000001 | 0.000000 | 0 | 0 |
| Sending data | 0.133695 | 0.133527 | 0.000000 | 0 | 0 |
| end | 0.000016 | 0.000009 | 0.000000 | 0 | 0 |
| query end | 0.000009 | 0.000009 | 0.000000 | 0 | 0 |
| closing tables | 0.000008 | 0.000008 | 0.000000 | 0 | 0 |
| freeing items | 0.000017 | 0.000017 | 0.000000 | 0 | 0 |
| cleaning up | 0.000009 | 0.000009 | 0.000000 | 0 | 0 |
+----------------------+----------+----------+------------+--------------+---------------+
15 rows in set, 1 warning (0.00 sec)
[email protected]#mysql.sock : tc0112:41:27>select count(*) from test2 use index (PRIMARY);
+----------+
| count(*) |
+----------+
| 1120198 |
+----------+
1 row in set (0.15 sec)
[email protected]#mysql.sock : tc0112:41:56>show profile cpu,block io for query 4;
+----------------------+----------+----------+------------+--------------+---------------+
| Status | Duration | CPU_user | CPU_system | Block_ops_in | Block_ops_out |
+----------------------+----------+----------+------------+--------------+---------------+
| starting | 0.000052 | 0.000036 | 0.000010 | 0 | 0 |
| checking permissions | 0.000005 | 0.000003 | 0.000001 | 0 | 0 |
| Opening tables | 0.000013 | 0.000011 | 0.000004 | 0 | 0 |
| init | 0.000010 | 0.000007 | 0.000002 | 0 | 0 |
| System lock | 0.000006 | 0.000005 | 0.000001 | 0 | 0 |
| optimizing | 0.000003 | 0.000002 | 0.000001 | 0 | 0 |
| statistics | 0.000010 | 0.000008 | 0.000002 | 0 | 0 |
| preparing | 0.000008 | 0.000006 | 0.000002 | 0 | 0 |
| executing | 0.000002 | 0.000001 | 0.000000 | 0 | 0 |
| Sending data | 0.149678 | 0.149268 | 0.000191 | 0 | 0 |
| end | 0.000014 | 0.000006 | 0.000002 | 0 | 0 |
| query end | 0.000009 | 0.000007 | 0.000002 | 0 | 0 |
| closing tables | 0.000008 | 0.000006 | 0.000002 | 0 | 0 |
| freeing items | 0.000014 | 0.000011 | 0.000003 | 0 | 0 |
| cleaning up | 0.000015 | 0.000011 | 0.000003 | 0 | 0 |
+----------------------+----------+----------+------------+--------------+---------------+
15 rows in set, 1 warning (0.00 sec)
The difference is mainly in Sending data part ,Sending data Include “ collect + send out " data .
see optimizer_trace
[email protected]#mysql.sock : tc0112:45:02>set optimizer_trace='enabled=on';
Query OK, 0 rows affected (0.00 sec)
[email protected]#mysql.sock : tc0112:46:05>set optimizer_trace_max_mem_size=1000000;
Query OK, 0 rows affected (0.00 sec)
[email protected]#mysql.sock : tc0112:46:11>set end_markers_in_json=on;
Query OK, 0 rows affected (0.00 sec)
[email protected]#mysql.sock : tc0112:46:16>select count(*) from test2;
+----------+
| count(*) |
+----------+
| 1120198 |
+----------+
1 row in set (0.13 sec)
[email protected]#mysql.sock : tc0112:46:22>select * from information_schema.optimizer_trace\G
*************************** 1. row ***************************
QUERY: select count(*) from test2
TRACE: {
"steps": [
{
"join_preparation": {
"select#": 1,
"steps": [
{
"expanded_query": "/* select#1 */ select count(0) AS `count(*)` from `test2`"
}
] /* steps */
} /* join_preparation */
},
{
"join_optimization": {
"select#": 1,
"steps": [
{
"table_dependencies": [
{
"table": "`test2`",
"row_may_be_null": false,
"map_bit": 0,
"depends_on_map_bits": [
] /* depends_on_map_bits */
}
] /* table_dependencies */
},
{
"rows_estimation": [
{
"table": "`test2`",
"table_scan": {
"rows": 1114117,
"cost": 6375
} /* table_scan */
}
] /* rows_estimation */
},
{
"considered_execution_plans": [
{
"plan_prefix": [
] /* plan_prefix */,
"table": "`test2`",
"best_access_path": {
"considered_access_paths": [
{
"rows_to_scan": 1114117,
"access_type": "scan",
"resulting_rows": 1.11e6,
"cost": 229198,
"chosen": true
}
] /* considered_access_paths */
} /* best_access_path */,
"condition_filtering_pct": 100,
"rows_for_plan": 1.11e6,
"cost_for_plan": 229198,
"chosen": true
}
] /* considered_execution_plans */
},
{
"attaching_conditions_to_tables": {
"original_condition": null,
"attached_conditions_computation": [
] /* attached_conditions_computation */,
"attached_conditions_summary": [
{
"table": "`test2`",
"attached": null
}
] /* attached_conditions_summary */
} /* attaching_conditions_to_tables */
},
{
"refine_plan": [
{
"table": "`test2`"
}
] /* refine_plan */
}
] /* steps */
} /* join_optimization */
},
{
"join_execution": {
"select#": 1,
"steps": [
] /* steps */
} /* join_execution */
}
] /* steps */
}
MISSING_BYTES_BEYOND_MAX_MEM_SIZE: 0
INSUFFICIENT_PRIVILEGES: 0
1 row in set (0.00 sec)
[email protected]#mysql.sock : tc0112:46:33>
[email protected]#mysql.sock : tc0104:49:23>select * from information_schema.optimizer_trace\G
*************************** 1. row ***************************
QUERY: select count(*) from test2 use index (PRIMARY)
TRACE: {
"steps": [
{
"join_preparation": {
"select#": 1,
"steps": [
{
"expanded_query": "/* select#1 */ select count(0) AS `count(*)` from `test2` USE INDEX (PRIMARY)"
}
] /* steps */
} /* join_preparation */
},
{
"join_optimization": {
"select#": 1,
"steps": [
{
"table_dependencies": [
{
"table": "`test2` USE INDEX (PRIMARY)",
"row_may_be_null": false,
"map_bit": 0,
"depends_on_map_bits": [
] /* depends_on_map_bits */
}
] /* table_dependencies */
},
{
"rows_estimation": [
{
"table": "`test2` USE INDEX (PRIMARY)",
"table_scan": {
"rows": 1114117,
"cost": 6375
} /* table_scan */
}
] /* rows_estimation */
},
{
"considered_execution_plans": [
{
"plan_prefix": [
] /* plan_prefix */,
"table": "`test2` USE INDEX (PRIMARY)",
"best_access_path": {
"considered_access_paths": [
{
"rows_to_scan": 1114117,
"access_type": "scan",
"resulting_rows": 1.11e6,
"cost": 229198,
"chosen": true
}
] /* considered_access_paths */
} /* best_access_path */,
"condition_filtering_pct": 100,
"rows_for_plan": 1.11e6,
"cost_for_plan": 229198,
"chosen": true
}
] /* considered_execution_plans */
},
{
"attaching_conditions_to_tables": {
"original_condition": null,
"attached_conditions_computation": [
] /* attached_conditions_computation */,
"attached_conditions_summary": [
{
"table": "`test2` USE INDEX (PRIMARY)",
"attached": null
}
] /* attached_conditions_summary */
} /* attaching_conditions_to_tables */
},
{
"refine_plan": [
{
"table": "`test2` USE INDEX (PRIMARY)"
}
] /* refine_plan */
}
] /* steps */
} /* join_optimization */
},
{
"join_execution": {
"select#": 1,
"steps": [
] /* steps */
} /* join_execution */
}
] /* steps */
}
MISSING_BYTES_BEYOND_MAX_MEM_SIZE: 0
INSUFFICIENT_PRIVILEGES: 0
1 row in set (0.00 sec)
According to the collection of optimizer_trace Information , I didn't see the difference .
Use strace analysis
Commands used
strace -o ./xxxx.log -T -tt -f -p `pidof mysqld`
The main contents collected are as follows ：
2779 17:31:57.090832 recvfrom(19, "\3select count(*) from test2", 27, MSG_DONTWAIT, NULL, NULL) = 27 <0.000011>
2746 17:31:57.131173 <... futex resumed> ) = -1 ETIMEDOUT (Connection timed out) <1.000589>
2746 17:31:57.131221 futex(0x3176e68, FUTEX_WAKE_PRIVATE, 1) = 0 <0.000009>
2746 17:31:57.131471 futex(0x3176e94, FUTEX_WAIT_BITSET_PRIVATE|FUTEX_CLOCK_REALTIME, 388151, {1593250318, 131449000}, ffffffff <unfinished ...>
2745 17:31:57.198173 <... futex resumed> ) = -1 ETIMEDOUT (Connection timed out) <1.000774>
2745 17:31:57.198219 futex(0x420a018, FUTEX_WAKE_PRIVATE, 1) = 0 <0.000008>
2745 17:31:57.198251 futex(0x420a044, FUTEX_WAIT_BITSET_PRIVATE|FUTEX_CLOCK_REALTIME, 388233, {1593250318, 198244000}, ffffffff <unfinished ...>
2779 17:31:57.221047 sendto(19, "\1\0\0\1\1\36\0\0\2\3def\0\0\0\10count(*)\0\f?\0\25\0\0"..., 62, MSG_DONTWAIT, NULL, 0) = 62 <0.000157>
2779 17:31:57.221269 recvfrom(19, 0x57addc0, 4, MSG_DONTWAIT, NULL, NULL) = -1 EAGAIN (Resource temporarily unavailable) <0.000009>
2779 17:31:57.221303 poll([{fd=19, events=POLLIN|POLLPRI}], 1, 600000 <unfinished ...>
2779 17:32:21.413376 recvfrom(19, "\3select count(*) from test2 use "..., 47, MSG_DONTWAIT, NULL, NULL) = 47 <0.000010>
2748 17:32:21.446209 <... nanosleep resumed> NULL) = 0 <1.009241>
2748 17:32:21.446265 nanosleep({1, 0}, <unfinished ...>
2738 17:32:21.501216 <... futex resumed> ) = -1 ETIMEDOUT (Connection timed out) <1.007208>
2738 17:32:21.501262 futex(0x3177018, FUTEX_WAKE_PRIVATE, 1) = 0 <0.000008>
2738 17:32:21.501297 futex(0x3177044, FUTEX_WAIT_BITSET_PRIVATE|FUTEX_CLOCK_REALTIME, 388723, {1593250342, 501290000}, ffffffff <unfinished ...>
2737 17:32:21.523241 <... io_getevents resumed> [], {0, 500000000}) = 0 <0.510550>
2736 17:32:21.523280 <... io_getevents resumed> [], {0, 500000000}) = 0 <0.510589>
2735 17:32:21.523287 <... io_getevents resumed> [], {0, 500000000}) = 0 <0.510591>
2734 17:32:21.523292 <... io_getevents resumed> [], {0, 500000000}) = 0 <0.510593>
2733 17:32:21.523298 <... io_getevents resumed> [], {0, 500000000}) = 0 <0.510594>
2732 17:32:21.523303 <... io_getevents resumed> [], {0, 500000000}) = 0 <0.510597>
2731 17:32:21.523309 <... io_getevents resumed> [], {0, 500000000}) = 0 <0.510598>
2730 17:32:21.523314 <... io_getevents resumed> [], {0, 500000000}) = 0 <0.510600>
2729 17:32:21.523319 <... io_getevents resumed> [], {0, 500000000}) = 0 <0.510601>
2728 17:32:21.523324 <... io_getevents resumed> [], {0, 500000000}) = 0 <0.510594>
2737 17:32:21.523368 io_getevents(140091831586816, 1, 256, <unfinished ...>
2736 17:32:21.523377 io_getevents(140091831599104, 1, 256, <unfinished ...>
2735 17:32:21.523382 io_getevents(140091831611392, 1, 256, <unfinished ...>
2734 17:32:21.523385 io_getevents(140091831623680, 1, 256, <unfinished ...>
2733 17:32:21.523389 io_getevents(140091831926784, 1, 256, <unfinished ...>
2732 17:32:21.523393 io_getevents(140091831939072, 1, 256, <unfinished ...>
2731 17:32:21.523397 io_getevents(140092021788672, 1, 256, <unfinished ...>
2730 17:32:21.523401 io_getevents(140092021800960, 1, 256, <unfinished ...>
2729 17:32:21.523405 io_getevents(140091831902208, 1, 256, <unfinished ...>
2728 17:32:21.523408 io_getevents(140091831914496, 1, 256, <unfinished ...>
2779 17:32:21.563856 sendto(19, "\1\0\0\1\1\36\0\0\2\3def\0\0\0\10count(*)\0\f?\0\25\0\0"..., 62, MSG_DONTWAIT, NULL, 0) = 62 <0.000103>
2779 17:32:21.564086 recvfrom(19, 0x57addc0, 4, MSG_DONTWAIT, NULL, NULL) = -1 EAGAIN (Resource temporarily unavailable) <0.000008>
2779 17:32:21.564120 poll([{fd=19, events=POLLIN|POLLPRI}], 1, 600000 <unfinished ...>
We found that there are more steps to use the primary key query , Naturally, it's time-consuming .
Check it out. SQL The logical reading situation of
[email protected]#mysql.sock : tc0105:39:52>show status like 'innodb_buffer%';
+---------------------------------------+--------------------------------------------------+
| Variable_name | Value |
+---------------------------------------+--------------------------------------------------+
| Innodb_buffer_pool_dump_status | Dumping of buffer pool not started |
| Innodb_buffer_pool_load_status | Buffer pool(s) load completed at 200625 11:36:26 |
| Innodb_buffer_pool_resize_status | |
| Innodb_buffer_pool_pages_data | 21727 |
| Innodb_buffer_pool_bytes_data | 355975168 |
| Innodb_buffer_pool_pages_dirty | 0 |
| Innodb_buffer_pool_bytes_dirty | 0 |
| Innodb_buffer_pool_pages_flushed | 353199 |
| Innodb_buffer_pool_pages_free | 11017 |
| Innodb_buffer_pool_pages_misc | 24 |
| Innodb_buffer_pool_pages_total | 32768 |
| Innodb_buffer_pool_read_ahead_rnd | 0 |
| Innodb_buffer_pool_read_ahead | 0 |
| Innodb_buffer_pool_read_ahead_evicted | 0 |
| Innodb_buffer_pool_read_requests | 120950072 |
| Innodb_buffer_pool_reads | 576 |
| Innodb_buffer_pool_wait_free | 0 |
| Innodb_buffer_pool_write_requests | 13289147 |
+---------------------------------------+--------------------------------------------------+
18 rows in set (0.00 sec)
[email protected]#mysql.sock : tc0105:39:54>select count(*) from test2;
+----------+
| count(*) |
+----------+
| 1120198 |
+----------+
1 row in set (0.13 sec)
[email protected]#mysql.sock : tc0105:39:57>show status like 'innodb_buffer%';
+---------------------------------------+--------------------------------------------------+
| Variable_name | Value |
+---------------------------------------+--------------------------------------------------+
| Innodb_buffer_pool_dump_status | Dumping of buffer pool not started |
| Innodb_buffer_pool_load_status | Buffer pool(s) load completed at 200625 11:36:26 |
| Innodb_buffer_pool_resize_status | |
| Innodb_buffer_pool_pages_data | 21727 |
| Innodb_buffer_pool_bytes_data | 355975168 |
| Innodb_buffer_pool_pages_dirty | 0 |
| Innodb_buffer_pool_bytes_dirty | 0 |
| Innodb_buffer_pool_pages_flushed | 353199 |
| Innodb_buffer_pool_pages_free | 11017 |
| Innodb_buffer_pool_pages_misc | 24 |
| Innodb_buffer_pool_pages_total | 32768 |
| Innodb_buffer_pool_read_ahead_rnd | 0 |
| Innodb_buffer_pool_read_ahead | 0 |
| Innodb_buffer_pool_read_ahead_evicted | 0 |
| Innodb_buffer_pool_read_requests | 121076043 |
| Innodb_buffer_pool_reads | 576 |
| Innodb_buffer_pool_wait_free | 0 |
| Innodb_buffer_pool_write_requests | 13289147 |
+---------------------------------------+--------------------------------------------------+
18 rows in set (0.00 sec)
[email protected]#mysql.sock : tc0105:39:59>
121076043-120950072=125971
[email protected]#mysql.sock : tc0105:40:30>show status like 'innodb_buffer%';
+---------------------------------------+--------------------------------------------------+
| Variable_name | Value |
+---------------------------------------+--------------------------------------------------+
| Innodb_buffer_pool_dump_status | Dumping of buffer pool not started |
| Innodb_buffer_pool_load_status | Buffer pool(s) load completed at 200625 11:36:26 |
| Innodb_buffer_pool_resize_status | |
| Innodb_buffer_pool_pages_data | 21728 |
| Innodb_buffer_pool_bytes_data | 355991552 |
| Innodb_buffer_pool_pages_dirty | 0 |
| Innodb_buffer_pool_bytes_dirty | 0 |
| Innodb_buffer_pool_pages_flushed | 353303 |
| Innodb_buffer_pool_pages_free | 11016 |
| Innodb_buffer_pool_pages_misc | 24 |
| Innodb_buffer_pool_pages_total | 32768 |
| Innodb_buffer_pool_read_ahead_rnd | 0 |
| Innodb_buffer_pool_read_ahead | 0 |
| Innodb_buffer_pool_read_ahead_evicted | 0 |
| Innodb_buffer_pool_read_requests | 121120574 |
| Innodb_buffer_pool_reads | 576 |
| Innodb_buffer_pool_wait_free | 0 |
| Innodb_buffer_pool_write_requests | 13289849 |
+---------------------------------------+--------------------------------------------------+
18 rows in set (0.00 sec)
[email protected]#mysql.sock : tc0105:40:31>select count(*) from test2 use index (PRIMARY);
+----------+
| count(*) |
+----------+
| 1120198 |
+----------+
1 row in set (0.15 sec)
[email protected]#mysql.sock : tc0105:40:33>show status like 'innodb_buffer%';
+---------------------------------------+--------------------------------------------------+
| Variable_name | Value |
+---------------------------------------+--------------------------------------------------+
| Innodb_buffer_pool_dump_status | Dumping of buffer pool not started |
| Innodb_buffer_pool_load_status | Buffer pool(s) load completed at 200625 11:36:26 |
| Innodb_buffer_pool_resize_status | |
| Innodb_buffer_pool_pages_data | 21728 |
| Innodb_buffer_pool_bytes_data | 355991552 |
| Innodb_buffer_pool_pages_dirty | 0 |
| Innodb_buffer_pool_bytes_dirty | 0 |
| Innodb_buffer_pool_pages_flushed | 353303 |
| Innodb_buffer_pool_pages_free | 11016 |
| Innodb_buffer_pool_pages_misc | 24 |
| Innodb_buffer_pool_pages_total | 32768 |
| Innodb_buffer_pool_read_ahead_rnd | 0 |
| Innodb_buffer_pool_read_ahead | 0 |
| Innodb_buffer_pool_read_ahead_evicted | 0 |
| Innodb_buffer_pool_read_requests | 121251637 |
| Innodb_buffer_pool_reads | 576 |
| Innodb_buffer_pool_wait_free | 0 |
| Innodb_buffer_pool_write_requests | 13289849 |
+---------------------------------------+--------------------------------------------------+
18 rows in set (0.00 sec)
121251637-121120574=131063
Innodb_buffer_pool_read_requests Go to the primary key query 131063, Don't use the primary key 125971, Difference between 5092.
Summary
- The execution plan is different , and MySQL Of CBO The algorithm is about , Use optimizer_trace There's no difference , We will not continue to analyze , If other experts have a better way to share .
- The logical read difference is related to the index fields used .
- Provided here MySQL Some analysis ideas and methods of , For your reference .
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Single chip Bluetooth wireless burning
First use of dosbox
使用rtknavi进行RT-PPP测试
MySQL takes up too much memory solution
Naive Bayesian theory derivation
Liste des boucles de l'interface graphique de défaillance
随机推荐
SVN更新后不出现红色感叹号
Lock wait timeout exceeded try restarting transaction
Fairygui character status Popup
Redis based distributed locks and ultra detailed improvement ideas
（5） Introduction to R language bioinformatics -- ORF and sequence analysis
GPS高程拟合抗差中误差的求取代码实现
Unity scene jump and exit
Postman 中级使用教程【环境变量、测试脚本、断言、接口文档等】
Expected value (EV)
关于Gateway中使用@Controller的问题
Gateway 根据服务名路由失败，报错 Service Unavailable, status=503
程序设计大作业：教务管理系统（C语言）
Office提示您的许可证不是正版弹框解决
编译原理：源程序的预处理及词法分析程序的设计与实现（含代码）
Affichage du changement de valeur du Buff de gain de l'interface graphique de défaillance
Derivation of logistic regression theory
Common DOS commands
[leetcode19] delete the penultimate node in the linked list
FGUI工程打包发布＆导入Unity＆将UI显示出来的方式
Mixed use of fairygui button dynamics