Metrics Schema
The METRICS_SCHEMA
is a set of views on top of TiDB metrics that are stored in Prometheus. The source of the PromQL (Prometheus Query Language) for each of the tables is available in INFORMATION_SCHEMA.METRICS_TABLES
.
USE metrics_schema;
SELECT * FROM uptime;
SELECT * FROM information_schema.metrics_tables WHERE table_name='uptime'\G
+----------------------------+-----------------+------------+--------------------+
| time | instance | job | value |
+----------------------------+-----------------+------------+--------------------+
| 2020-07-06 15:26:26.203000 | 127.0.0.1:10080 | tidb | 123.60300016403198 |
| 2020-07-06 15:27:26.203000 | 127.0.0.1:10080 | tidb | 183.60300016403198 |
| 2020-07-06 15:26:26.203000 | 127.0.0.1:20180 | tikv | 123.60300016403198 |
| 2020-07-06 15:27:26.203000 | 127.0.0.1:20180 | tikv | 183.60300016403198 |
| 2020-07-06 15:26:26.203000 | 127.0.0.1:2379 | pd | 123.60300016403198 |
| 2020-07-06 15:27:26.203000 | 127.0.0.1:2379 | pd | 183.60300016403198 |
| 2020-07-06 15:26:26.203000 | 127.0.0.1:9090 | prometheus | 123.72300004959106 |
| 2020-07-06 15:27:26.203000 | 127.0.0.1:9090 | prometheus | 183.72300004959106 |
+----------------------------+-----------------+------------+--------------------+
8 rows in set (0.00 sec)
*************************** 1. row ***************************
TABLE_NAME: uptime
PROMQL: (time() - process_start_time_seconds{$LABEL_CONDITIONS})
LABELS: instance,job
QUANTILE: 0
COMMENT: TiDB uptime since last restart(second)
1 row in set (0.00 sec)
SHOW TABLES;
+---------------------------------------------------+
| Tables_in_metrics_schema |
+---------------------------------------------------+
| abnormal_stores |
| etcd_disk_wal_fsync_rate |
| etcd_wal_fsync_duration |
| etcd_wal_fsync_total_count |
| etcd_wal_fsync_total_time |
| go_gc_count |
| go_gc_cpu_usage |
| go_gc_duration |
| go_heap_mem_usage |
| go_threads |
| goroutines_count |
| node_cpu_usage |
| node_disk_available_size |
| node_disk_io_util |
| node_disk_iops |
| node_disk_read_latency |
| node_disk_size |
..
| tikv_storage_async_request_total_time |
| tikv_storage_async_requests |
| tikv_storage_async_requests_total_count |
| tikv_storage_command_ops |
| tikv_store_size |
| tikv_thread_cpu |
| tikv_thread_nonvoluntary_context_switches |
| tikv_thread_voluntary_context_switches |
| tikv_threads_io |
| tikv_threads_state |
| tikv_total_keys |
| tikv_wal_sync_duration |
| tikv_wal_sync_max_duration |
| tikv_worker_handled_tasks |
| tikv_worker_handled_tasks_total_num |
| tikv_worker_pending_tasks |
| tikv_worker_pending_tasks_total_num |
| tikv_write_stall_avg_duration |
| tikv_write_stall_max_duration |
| tikv_write_stall_reason |
| up |
| uptime |
+---------------------------------------------------+
626 rows in set (0.00 sec)
The METRICS_SCHEMA
is used as a data source for monitoring-related summary tables such as (metrics_summary
, metrics_summary_by_label
and inspection_summary
.
Additional Examples
Taking the tidb_query_duration
monitoring table in metrics_schema
as an example, this section illustrates how to use this monitoring table and how it works. The working principles of other monitoring tables are similar to tidb_query_duration
.
Query the information related to the tidb_query_duration
table on information_schema.metrics_tables
:
SELECT * FROM information_schema.metrics_tables WHERE table_name='tidb_query_duration';
+---------------------+----------------------------------------------------------------------------------------------------------------------------------------------------------+-------------------+----------+----------------------------------------------+
| TABLE_NAME | PROMQL | LABELS | QUANTILE | COMMENT |
+---------------------+----------------------------------------------------------------------------------------------------------------------------------------------------------+-------------------+----------+----------------------------------------------+
| tidb_query_duration | histogram_quantile($QUANTILE, sum(rate(tidb_server_handle_query_duration_seconds_bucket{$LABEL_CONDITIONS}[$RANGE_DURATION])) by (le,sql_type,instance)) | instance,sql_type | 0.9 | The quantile of TiDB query durations(second) |
+---------------------+----------------------------------------------------------------------------------------------------------------------------------------------------------+-------------------+----------+----------------------------------------------+
Field description:
TABLE_NAME
: Corresponds to the table name inmetrics_schema
. In this example, the table name istidb_query_duration
.PROMQL
: The working principle of the monitoring table is to first map SQL statements toPromQL
, then to request data from Prometheus, and to convert Prometheus results into SQL query results. This field is the expression template ofPromQL
. When you query the data of the monitoring table, the query conditions are used to rewrite the variables in this template to generate the final query expression.LABELS
: The label for the monitoring item.tidb_query_duration
has two labels:instance
andsql_type
.QUANTILE
: The percentile. For monitoring data of the histogram type, a default percentile is specified. If the value of this field is0
, it means that the monitoring item corresponding to the monitoring table is not a histogram.COMMENT
: Explanations for the monitoring table. You can see that thetidb_query_duration
table is used to query the percentile time of the TiDB query execution, such as the query time of P999/P99/P90. The unit is second.
To query the schema of the tidb_query_duration
table, execute the following statement:
SHOW CREATE TABLE metrics_schema.tidb_query_duration;
+---------------------+--------------------------------------------------------------------------------------------------------------------+
| Table | Create Table |
+---------------------+--------------------------------------------------------------------------------------------------------------------+
| tidb_query_duration | CREATE TABLE `tidb_query_duration` ( |
| | `time` datetime unsigned DEFAULT CURRENT_TIMESTAMP, |
| | `instance` varchar(512) DEFAULT NULL, |
| | `sql_type` varchar(512) DEFAULT NULL, |
| | `quantile` double unsigned DEFAULT '0.9', |
| | `value` double unsigned DEFAULT NULL |
| | ) ENGINE=InnoDB DEFAULT CHARSET=utf8mb4 COLLATE=utf8mb4_bin COMMENT='The quantile of TiDB query durations(second)' |
+---------------------+--------------------------------------------------------------------------------------------------------------------+
time
: The time of the monitoring item.instance
andsql_type
: The labels of thetidb_query_duration
monitoring item.instance
means the monitoring address.sql_type
means the type of the executed SQL statement.quantile
: The percentile. The monitoring item of the histogram type has this column, which indicates the percentile time of the query. For example,quantile = 0.9
means to query the time of P90.value
: The value of the monitoring item.
The following statement queries the P99 time within the range of [2020-03-25 23:40:00
, 2020-03-25 23:42:00
].
SELECT * FROM metrics_schema.tidb_query_duration WHERE value is not null AND time>='2020-03-25 23:40:00' AND time <= '2020-03-25 23:42:00' AND quantile=0.99;
+---------------------+-------------------+----------+----------+----------------+
| time | instance | sql_type | quantile | value |
+---------------------+-------------------+----------+----------+----------------+
| 2020-03-25 23:40:00 | 172.16.5.40:10089 | Insert | 0.99 | 0.509929485256 |
| 2020-03-25 23:41:00 | 172.16.5.40:10089 | Insert | 0.99 | 0.494690793986 |
| 2020-03-25 23:42:00 | 172.16.5.40:10089 | Insert | 0.99 | 0.493460506934 |
| 2020-03-25 23:40:00 | 172.16.5.40:10089 | Select | 0.99 | 0.152058493415 |
| 2020-03-25 23:41:00 | 172.16.5.40:10089 | Select | 0.99 | 0.152193879678 |
| 2020-03-25 23:42:00 | 172.16.5.40:10089 | Select | 0.99 | 0.140498483232 |
| 2020-03-25 23:40:00 | 172.16.5.40:10089 | internal | 0.99 | 0.47104 |
| 2020-03-25 23:41:00 | 172.16.5.40:10089 | internal | 0.99 | 0.11776 |
| 2020-03-25 23:42:00 | 172.16.5.40:10089 | internal | 0.99 | 0.11776 |
+---------------------+-------------------+----------+----------+----------------+
The first row of the query result above means that at the time of 2020-03-25 23:40:00, on the TiDB instance 172.16.5.40:10089
, the P99 execution time of the Insert
type statement is 0.509929485256 seconds. The meanings of other rows are similar. Other values of the sql_type
column are described as follows:
Select
: Theselect
type statement is executed.internal
: The internal SQL statement of TiDB, which is used to update the statistical information and get the global variables.
To view the execution plan of the statement above, execute the following statement:
DESC SELECT * FROM metrics_schema.tidb_query_duration WHERE value is not null AND time>='2020-03-25 23:40:00' AND time <= '2020-03-25 23:42:00' AND quantile=0.99;
+------------------+----------+------+---------------------------+--------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+
| id | estRows | task | access object | operator info |
+------------------+----------+------+---------------------------+--------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+
| Selection_5 | 8000.00 | root | | not(isnull(Column#5)) |
| └─MemTableScan_6 | 10000.00 | root | table:tidb_query_duration | PromQL:histogram_quantile(0.99, sum(rate(tidb_server_handle_query_duration_seconds_bucket{}[60s])) by (le,sql_type,instance)), start_time:2020-03-25 23:40:00, end_time:2020-03-25 23:42:00, step:1m0s |
+------------------+----------+------+---------------------------+--------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+
From the result above, you can see that PromQL
, start_time
, end_time
, and step
are in the execution plan. During the execution process, TiDB calls the query_range
HTTP API of Prometheus to query the monitoring data.
You might find that in the range of [2020-03-25 23:40:00
, 2020-03-25 23:42:00
], each label only has three time values. In the execution plan, the value of step
is 1 minute, which means that the interval of these values is 1 minute. step
is determined by the following two session variables:
tidb_metric_query_step
: The query resolution step width. To get thequery_range
data from Prometheus, you need to specifystart_time
,end_time
, andstep
.step
uses the value of this variable.tidb_metric_query_range_duration
: When the monitoring data is queried, the value of the$ RANGE_DURATION
field inPROMQL
is replaced with the value of this variable. The default value is 60 seconds.
To view the values of monitoring items with different granularities, you can modify the two session variables above before querying the monitoring table. For example:
Modify the values of the two session variables and set the time granularity to 30 seconds.
set @@tidb_metric_query_step=30; set @@tidb_metric_query_range_duration=30;Query the
tidb_query_duration
monitoring item as follows. From the result, you can see that within the 3-minute time range, each label has 6 time values, and the interval between each value is 30 seconds.select * from metrics_schema.tidb_query_duration where value is not null and time>='2020-03-25 23:40:00' and time <= '2020-03-25 23:42:00' and quantile=0.99;+---------------------+-------------------+----------+----------+-----------------+ | time | instance | sql_type | quantile | value | +---------------------+-------------------+----------+----------+-----------------+ | 2020-03-25 23:40:00 | 172.16.5.40:10089 | Insert | 0.99 | 0.483285651924 | | 2020-03-25 23:40:30 | 172.16.5.40:10089 | Insert | 0.99 | 0.484151462113 | | 2020-03-25 23:41:00 | 172.16.5.40:10089 | Insert | 0.99 | 0.504576 | | 2020-03-25 23:41:30 | 172.16.5.40:10089 | Insert | 0.99 | 0.493577384561 | | 2020-03-25 23:42:00 | 172.16.5.40:10089 | Insert | 0.99 | 0.49482474311 | | 2020-03-25 23:40:00 | 172.16.5.40:10089 | Select | 0.99 | 0.189253402185 | | 2020-03-25 23:40:30 | 172.16.5.40:10089 | Select | 0.99 | 0.184224951851 | | 2020-03-25 23:41:00 | 172.16.5.40:10089 | Select | 0.99 | 0.151673410553 | | 2020-03-25 23:41:30 | 172.16.5.40:10089 | Select | 0.99 | 0.127953838989 | | 2020-03-25 23:42:00 | 172.16.5.40:10089 | Select | 0.99 | 0.127455434547 | | 2020-03-25 23:40:00 | 172.16.5.40:10089 | internal | 0.99 | 0.0624 | | 2020-03-25 23:40:30 | 172.16.5.40:10089 | internal | 0.99 | 0.12416 | | 2020-03-25 23:41:00 | 172.16.5.40:10089 | internal | 0.99 | 0.0304 | | 2020-03-25 23:41:30 | 172.16.5.40:10089 | internal | 0.99 | 0.06272 | | 2020-03-25 23:42:00 | 172.16.5.40:10089 | internal | 0.99 | 0.0629333333333 | +---------------------+-------------------+----------+----------+-----------------+View the execution plan. From the result, you can also see that the values of
PromQL
andstep
in the execution plan have been changed to 30 seconds.desc select * from metrics_schema.tidb_query_duration where value is not null and time>='2020-03-25 23:40:00' and time <= '2020-03-25 23:42:00' and quantile=0.99;+------------------+----------+------+---------------------------+-------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+ | id | estRows | task | access object | operator info | +------------------+----------+------+---------------------------+-------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+ | Selection_5 | 8000.00 | root | | not(isnull(Column#5)) | | └─MemTableScan_6 | 10000.00 | root | table:tidb_query_duration | PromQL:histogram_quantile(0.99, sum(rate(tidb_server_handle_query_duration_seconds_bucket{}[30s])) by (le,sql_type,instance)), start_time:2020-03-25 23:40:00, end_time:2020-03-25 23:42:00, step:30s | +------------------+----------+------+---------------------------+-------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+