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METRICS_SUMMARY
由于 TiDB 集群的监控指标数量较多,为了方便用户从众多监控中找出异常的监控项,TiDB 4.0 提供了以下监控汇总表:
information_schema.metrics_summary
information_schema.metrics_summary_by_label
这两张表用于汇总所有监控数据,用户排查各个监控指标会更有效率。其中 information_schema.metrics_summary_by_label
会对不同的 label 进行区分统计。
USE information_schema;
DESC metrics_summary;
+--------------+--------------+------+------+---------+-------+
| Field | Type | Null | Key | Default | Extra |
+--------------+--------------+------+------+---------+-------+
| METRICS_NAME | varchar(64) | YES | | NULL | |
| QUANTILE | double | YES | | NULL | |
| SUM_VALUE | double(22,6) | YES | | NULL | |
| AVG_VALUE | double(22,6) | YES | | NULL | |
| MIN_VALUE | double(22,6) | YES | | NULL | |
| MAX_VALUE | double(22,6) | YES | | NULL | |
| COMMENT | varchar(256) | YES | | NULL | |
+--------------+--------------+------+------+---------+-------+
7 rows in set (0.00 sec)
字段解释:
METRICS_NAME
:监控表名。QUANTILE
:百分位。可以通过 SQL 语句指定QUANTILE
,例如:select * from metrics_summary where quantile=0.99
指定查看百分位为 0.99 的数据。select * from metrics_summary where quantile in (0.80, 0.90, 0.99, 0.999)
同时查看百分位为 0.80, 0.90, 0.99, 0.999 的数据。
SUM_VALUE、AVG_VALUE、MIN_VALUE、MAX_VALUE
分别表示总和、平均值、最小值、最大值。COMMENT
:对应监控的解释。
具体查询示例:
查询 '2020-03-08 13:23:00', '2020-03-08 13:33:00'
时间范围内 TiDB 集群中平均耗时最高的三组监控项。可直接查询 information_schema.metrics_summary
表,并通过 /*+ time_range() */
这个 hint 来指定时间范围,构造的 SQL 语句如下:
SELECT /*+ time_range('2020-03-08 13:23:00','2020-03-08 13:33:00') */ *
FROM information_schema.metrics_summary
WHERE metrics_name LIKE 'tidb%duration'
AND avg_value > 0
AND quantile = 0.99
ORDER BY avg_value DESC
LIMIT 3\G
***************************[ 1. row ]***************************
METRICS_NAME | tidb_get_token_duration
QUANTILE | 0.99
SUM_VALUE | 8.972509
AVG_VALUE | 0.996945
MIN_VALUE | 0.996515
MAX_VALUE | 0.997458
COMMENT | The quantile of Duration (us) for getting token, it should be small until concurrency limit is reached(second)
***************************[ 2. row ]***************************
METRICS_NAME | tidb_query_duration
QUANTILE | 0.99
SUM_VALUE | 0.269079
AVG_VALUE | 0.007272
MIN_VALUE | 0.000667
MAX_VALUE | 0.01554
COMMENT | The quantile of TiDB query durations(second)
***************************[ 3. row ]***************************
METRICS_NAME | tidb_kv_request_duration
QUANTILE | 0.99
SUM_VALUE | 0.170232
AVG_VALUE | 0.004601
MIN_VALUE | 0.000975
MAX_VALUE | 0.013
COMMENT | The quantile of kv requests durations by store
类似的,查询 metrics_summary_by_label
监控汇总表示例如下:
SELECT /*+ time_range('2020-03-08 13:23:00','2020-03-08 13:33:00') */ *
FROM information_schema.metrics_summary_by_label
WHERE metrics_name LIKE 'tidb%duration'
AND avg_value > 0
AND quantile = 0.99
ORDER BY avg_value DESC
LIMIT 10\G
***************************[ 1. row ]***************************
INSTANCE | 172.16.5.40:10089
METRICS_NAME | tidb_get_token_duration
LABEL |
QUANTILE | 0.99
SUM_VALUE | 8.972509
AVG_VALUE | 0.996945
MIN_VALUE | 0.996515
MAX_VALUE | 0.997458
COMMENT | The quantile of Duration (us) for getting token, it should be small until concurrency limit is reached(second)
***************************[ 2. row ]***************************
INSTANCE | 172.16.5.40:10089
METRICS_NAME | tidb_query_duration
LABEL | Select
QUANTILE | 0.99
SUM_VALUE | 0.072083
AVG_VALUE | 0.008009
MIN_VALUE | 0.007905
MAX_VALUE | 0.008241
COMMENT | The quantile of TiDB query durations(second)
***************************[ 3. row ]***************************
INSTANCE | 172.16.5.40:10089
METRICS_NAME | tidb_query_duration
LABEL | Rollback
QUANTILE | 0.99
SUM_VALUE | 0.072083
AVG_VALUE | 0.008009
MIN_VALUE | 0.007905
MAX_VALUE | 0.008241
COMMENT | The quantile of TiDB query durations(second)
前文提到 metrics_summary_by_label
表结构相对于 metrics_summary
多了一列 LABEL
。以上面查询结果的第 2、3 行分别表示 tidb_query_duration
的 Select
和 Rollback
类型的语句平均耗时非常高。
除以上示例之外,监控汇总表可以通过对比两个时间段的全链路监控,迅速找出监控数据中变化最大的模块,快速定位瓶颈。以下示例对比两个时间段的所有监控(其中 t1 为 baseline),并按照差别最大的监控排序:
- 时间段 t1:
("2020-03-03 17:08:00", "2020-03-03 17:11:00")
- 时间段 t2:
("2020-03-03 17:18:00", "2020-03-03 17:21:00")
对两个时间段的监控按照 METRICS_NAME
进行 join,并按照差异值大小排序。其中 TIME_RANGE
是用于指定查询时间的 hint。
SELECT GREATEST(t1.avg_value,t2.avg_value)/LEAST(t1.avg_value,
t2.avg_value) AS ratio,
t1.metrics_name,
t1.avg_value as t1_avg_value,
t2.avg_value as t2_avg_value,
t2.comment
FROM
(SELECT /*+ time_range("2020-03-03 17:08:00", "2020-03-03 17:11:00")*/ *
FROM information_schema.metrics_summary ) t1
JOIN
(SELECT /*+ time_range("2020-03-03 17:18:00", "2020-03-03 17:21:00")*/ *
FROM information_schema.metrics_summary ) t2
ON t1.metrics_name = t2.metrics_name
ORDER BY ratio DESC LIMIT 10;
+----------------+------------------------------------------+----------------+------------------+---------------------------------------------------------------------------------------------+
| ratio | metrics_name | t1_avg_value | t2_avg_value | comment |
+----------------+------------------------------------------+----------------+------------------+---------------------------------------------------------------------------------------------+
| 5865.59537065 | tidb_slow_query_cop_process_total_time | 0.016333 | 95.804724 | The total time of TiDB slow query statistics with slow query total cop process time(second) |
| 3648.74109023 | tidb_distsql_partial_scan_key_total_num | 10865.666667 | 39646004.4394 | The total num of distsql partial scan key numbers |
| 267.002351165 | tidb_slow_query_cop_wait_total_time | 0.003333 | 0.890008 | The total time of TiDB slow query statistics with slow query total cop wait time(second) |
| 192.43267836 | tikv_cop_total_response_total_size | 2515333.66667 | 484032394.445 | |
| 192.43267836 | tikv_cop_total_response_size_per_seconds | 41922.227778 | 8067206.57408 | |
| 152.780296296 | tidb_distsql_scan_key_total_num | 5304.333333 | 810397.618317 | The total num of distsql scan numbers |
| 126.042290167 | tidb_distsql_execution_total_time | 0.421622 | 53.142143 | The total time of distsql execution(second) |
| 105.164020657 | tikv_cop_scan_details | 134.450733 | 14139.379665 | |
| 105.164020657 | tikv_cop_scan_details_total | 8067.043981 | 848362.77991 | |
| 101.635495394 | tikv_cop_scan_keys_num | 1070.875 | 108838.91113 | |
+----------------+------------------------------------------+----------------+------------------+---------------------------------------------------------------------------------------------+
上面查询结果表示:
- t2 时间段内的
tidb_slow_query_cop_process_total_time
(TiDB 慢查询中的cop process
耗时)比 t1 时间段高了 5865 倍。 - t2 时间段内的
tidb_distsql_partial_scan_key_total_num
(TiDB 的distsql
请求扫描 key 的数量)比 t1 时间段高了 3648 倍。 - t2 时间段内的
tidb_slow_query_cop_wait_total_time
(TiDB 慢查询中的 cop 请求排队等待的耗时)比 t1 时间段高了 267 倍。 - t2 时间段内的
tikv_cop_total_response_size
(TiKV 的 cop 请求结果的大小)比 t1 时间段高了 192 倍。 - t2 时间段内的
tikv_cop_scan_details
(TiKV 的 cop 请求的 scan)比 t1 时间段高了 105 倍。
综上,可以马上知道 t2 时间段的 cop 请求要比 t2 时间段高很多,导致 TiKV 的 Coprocessor 过载,出现了 cop task
等待,可以猜测可能是 t2 时间段出现了一些大查询,或者是查询较多的负载。
实际上,在 t1 ~ t2 整个时间段内都在跑 go-ycsb
的压测,然后在 t2 时间段跑了 20 个 tpch
的查询,所以是因为 tpch
大查询导致了出现很多的 cop 请求。