mysql的io与索引使用分析

项目中很多表由于接手人很多,所以管生不管养的建立了大量索引。
造成索引比数据大很多的奇葩现象,于是要找一找什么方式能方便的统计到索引的使用情况。
于是发现了performance_schema库中的表table_io_waits_summary_by_index_usage
它聚合了所有表索引I / O等待事件

从网上找到了不少可用的SQL语句来解决问题,同时还关注到了这几张表。
看描述就是系统优化的利器,虽然如今各种云RDS,能了解一些原生方式也是不错的。
尴尬的是阿里云RDS下面的表默认情况下是空的,所以只能用他们的性能分析优化工具了

table_io_waits_summary_by_index_usage: Table I/O waits per index
table_io_waits_summary_by_table: Table I/O waits per table
table_lock_waits_summary_by_table: Table lock waits per table

一些使用栗子

其实只用了第一个查询就满足了需求,其他的只是好奇玩玩,Ctrl + C而来
具体的可查询MySQL文档,如参考链接

查询具体库/表的索引使用情况

index_name为NULL则表示未使用索引,文档中提到插入语句被计入此项
TRUNCATE TABLE操作会重置表的值,更改表结构也可能会影响到统计

1
2
3
4
5
6
7
8
9
10
11
12
13
SELECT
object_type,
object_schema,
object_name,
index_name,
count_star,
count_read,
COUNT_FETCH
FROM
`performance_schema`.table_io_waits_summary_by_index_usage
WHERE
object_schema = 'database_name' AND
object_name ='table_name'

反映表的读写压力

1
2
3
4
5
6
7
8
SELECT file_name AS file,
count_read,
sum_number_of_bytes_read AS total_read,
count_write,
sum_number_of_bytes_write AS total_written,
(sum_number_of_bytes_read + sum_number_of_bytes_write) AS total
FROM `performance_schema`.file_summary_by_instance
ORDER BY sum_number_of_bytes_read+ sum_number_of_bytes_write DESC;

反映文件的延迟

1
2
3
4
5
6
7
8
9
SELECT (file_name) AS file,
count_star AS total,
CONCAT(ROUND(sum_timer_wait / 3600000000000000, 2), 'h') AS total_latency,
count_read,
CONCAT(ROUND(sum_timer_read / 1000000000000, 2), 's') AS read_latency,
count_write,
CONCAT(ROUND(sum_timer_write / 3600000000000000, 2), 'h')AS write_latency
FROM `performance_schema`.file_summary_by_instance
ORDER BY sum_timer_wait DESC;

table 的读写延迟

1
2
3
4
5
6
7
8
SELECT object_schema AS table_schema,
object_name AS table_name,
count_star AS total,
CONCAT(ROUND(sum_timer_wait / 3600000000000000, 2), 'h') as total_latency,
CONCAT(ROUND((sum_timer_wait / count_star) / 1000000, 2), 'us') AS avg_latency,
CONCAT(ROUND(max_timer_wait / 1000000000, 2), 'ms') AS max_latency
FROM `performance_schema`.objects_summary_global_by_type
ORDER BY sum_timer_wait DESC;

查看表操作频度

1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
SELECT object_schema AS table_schema,
object_name AS table_name,
count_star AS rows_io_total,
count_read AS rows_read,
count_write AS rows_write,
count_fetch AS rows_fetchs,
count_insert AS rows_inserts,
count_update AS rows_updates,
count_delete AS rows_deletes,
CONCAT(ROUND(sum_timer_fetch / 3600000000000000, 2), 'h') AS fetch_latency,
CONCAT(ROUND(sum_timer_insert / 3600000000000000, 2), 'h') AS insert_latency,
CONCAT(ROUND(sum_timer_update / 3600000000000000, 2), 'h') AS update_latency,
CONCAT(ROUND(sum_timer_delete / 3600000000000000, 2), 'h') AS delete_latency
FROM `performance_schema`.table_io_waits_summary_by_table
ORDER BY sum_timer_wait DESC ;

索引状况

1
2
3
4
5
6
7
8
9
10
11
12
13
14
SELECT OBJECT_SCHEMA AS table_schema,
OBJECT_NAME AS table_name,
INDEX_NAME as index_name,
COUNT_FETCH AS rows_fetched,
CONCAT(ROUND(SUM_TIMER_FETCH / 3600000000000000, 2), 'h') AS select_latency,
COUNT_INSERT AS rows_inserted,
CONCAT(ROUND(SUM_TIMER_INSERT / 3600000000000000, 2), 'h') AS insert_latency,
COUNT_UPDATE AS rows_updated,
CONCAT(ROUND(SUM_TIMER_UPDATE / 3600000000000000, 2), 'h') AS update_latency,
COUNT_DELETE AS rows_deleted,
CONCAT(ROUND(SUM_TIMER_DELETE / 3600000000000000, 2), 'h')AS delete_latency
FROM `performance_schema`.table_io_waits_summary_by_index_usage
WHERE index_name IS NOT NULL
ORDER BY sum_timer_wait DESC;

全表扫描情况

1
2
3
4
5
6
7
SELECT object_schema,
object_name,
count_read AS rows_full_scanned
FROM `performance_schema`.table_io_waits_summary_by_index_usage
WHERE index_name IS NULL
AND count_read > 0
ORDER BY count_read DESC;

没有使用的index

1
2
3
4
5
6
7
8
9
SELECT object_schema,
object_name,
index_name
FROM `performance_schema`.table_io_waits_summary_by_index_usage
WHERE index_name IS NOT NULL
AND count_star = 0
AND object_schema not in ('mysql','v_monitor')
AND index_name <> 'PRIMARY'
ORDER BY object_schema, object_name;

糟糕的sql问题摘要

1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
SELECT (DIGEST_TEXT) AS query,
SCHEMA_NAME AS db,
IF(SUM_NO_GOOD_INDEX_USED > 0 OR SUM_NO_INDEX_USED > 0, '*', '') AS full_scan,
COUNT_STAR AS exec_count,
SUM_ERRORS AS err_count,
SUM_WARNINGS AS warn_count,
(SUM_TIMER_WAIT) AS total_latency,
(MAX_TIMER_WAIT) AS max_latency,
(AVG_TIMER_WAIT) AS avg_latency,
(SUM_LOCK_TIME) AS lock_latency,
format(SUM_ROWS_SENT,0) AS rows_sent,
ROUND(IFNULL(SUM_ROWS_SENT / NULLIF(COUNT_STAR, 0), 0)) AS rows_sent_avg,
SUM_ROWS_EXAMINED AS rows_examined,
ROUND(IFNULL(SUM_ROWS_EXAMINED / NULLIF(COUNT_STAR, 0), 0)) AS rows_examined_avg,
SUM_CREATED_TMP_TABLES AS tmp_tables,
SUM_CREATED_TMP_DISK_TABLES AS tmp_disk_tables,
SUM_SORT_ROWS AS rows_sorted,
SUM_SORT_MERGE_PASSES AS sort_merge_passes,
DIGEST AS digest,
FIRST_SEEN AS first_seen,
LAST_SEEN as last_seen
FROM `performance_schema`.events_statements_summary_by_digest d
where d
ORDER BY SUM_TIMER_WAIT DESC
limit 20;

参考链接

Table I/O and Lock Wait Summary Tables