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INSPECTION_RESULT

TiDB has some built-in diagnostic rules for detecting faults and hidden issues in the system.

The INSPECTION_RESULT diagnostic feature can help you quickly find problems and reduce your repetitive manual work. You can use the select * from information_schema.inspection_result statement to trigger the internal diagnostics.

The structure of the information_schema.inspection_result diagnostic result table information_schema.inspection_result is as follows:

USE information_schema;
DESC inspection_result;
+----------------+--------------+------+------+---------+-------+
| Field          | Type         | Null | Key  | Default | Extra |
+----------------+--------------+------+------+---------+-------+
| RULE           | varchar(64)  | YES  |      | NULL    |       |
| ITEM           | varchar(64)  | YES  |      | NULL    |       |
| TYPE           | varchar(64)  | YES  |      | NULL    |       |
| INSTANCE       | varchar(64)  | YES  |      | NULL    |       |
| STATUS_ADDRESS | varchar(64)  | YES  |      | NULL    |       |
| VALUE          | varchar(64)  | YES  |      | NULL    |       |
| REFERENCE      | varchar(64)  | YES  |      | NULL    |       |
| SEVERITY       | varchar(64)  | YES  |      | NULL    |       |
| DETAILS        | varchar(256) | YES  |      | NULL    |       |
+----------------+--------------+------+------+---------+-------+
9 rows in set (0.00 sec)

Field description:

  • RULE: The name of the diagnostic rule. Currently, the following rules are available:
    • config: Checks whether the configuration is consistent and proper. If the same configuration is inconsistent on different instances, a warning diagnostic result is generated.
    • version: The consistency check of version. If the same version is inconsistent on different instances, a warning diagnostic result is generated.
    • node-load: Checks the server load. If the current system load is too high, the corresponding warning diagnostic result is generated.
    • critical-error: Each module of the system defines critical errors. If a critical error exceeds the threshold within the corresponding time period, a warning diagnostic result is generated.
    • threshold-check: The diagnostic system checks the thresholds of key metrics. If a threshold is exceeded, the corresponding diagnostic information is generated.
  • ITEM: Each rule diagnoses different items. This field indicates the specific diagnostic items corresponding to each rule.
  • TYPE: The instance type of the diagnostics. The optional values are tidb, pd, and tikv.
  • INSTANCE: The specific address of the diagnosed instance.
  • STATUS_ADDRESS: The HTTP API service address of the instance.
  • VALUE: The value of a specific diagnostic item.
  • REFERENCE: The reference value (threshold value) for this diagnostic item. If VALUE exceeds the threshold, the corresponding diagnostic information is generated.
  • SEVERITY: The severity level. The optional values are warning and critical.
  • DETAILS: Diagnostic details, which might also contain SQL statement(s) or document links for further diagnostics.

Diagnostics example

Diagnose issues currently existing in the cluster.

SELECT * FROM information_schema.inspection_result\G
***************************[ 1. row ]***************************
RULE      | config
ITEM      | log.slow-threshold
TYPE      | tidb
INSTANCE  | 172.16.5.40:4000
VALUE     | 0
REFERENCE | not 0
SEVERITY  | warning
DETAILS   | slow-threshold = 0 will record every query to slow log, it may affect performance
***************************[ 2. row ]***************************
RULE      | version
ITEM      | git_hash
TYPE      | tidb
INSTANCE  |
VALUE     | inconsistent
REFERENCE | consistent
SEVERITY  | critical
DETAILS   | the cluster has 2 different tidb version, execute the sql to see more detail: select * from information_schema.cluster_info where type='tidb'
***************************[ 3. row ]***************************
RULE      | threshold-check
ITEM      | storage-write-duration
TYPE      | tikv
INSTANCE  | 172.16.5.40:23151
VALUE     | 130.417
REFERENCE | < 0.100
SEVERITY  | warning
DETAILS   | max duration of 172.16.5.40:23151 tikv storage-write-duration was too slow
***************************[ 4. row ]***************************
RULE      | threshold-check
ITEM      | rocksdb-write-duration
TYPE      | tikv
INSTANCE  | 172.16.5.40:20151
VALUE     | 108.105
REFERENCE | < 0.100
SEVERITY  | warning
DETAILS   | max duration of 172.16.5.40:20151 tikv rocksdb-write-duration was too slow

The following issues can be detected from the diagnostic result above:

  • The first row indicates that TiDB's log.slow-threshold value is configured to 0, which might affect performance.
  • The second row indicates that two different TiDB versions exist in the cluster.
  • The third and fourth rows indicate that the TiKV write delay is too long. The expected delay is no more than 0.1 second, while the actual delay is far longer than expected.

You can also diagnose issues existing within a specified range, such as from "2020-03-26 00:03:00" to "2020-03-26 00:08:00". To specify the time range, use the SQL Hint of /*+ time_range() */. See the following query example:

select /*+ time_range("2020-03-26 00:03:00", "2020-03-26 00:08:00") */ * from information_schema.inspection_result\G
***************************[ 1. row ]***************************
RULE      | critical-error
ITEM      | server-down
TYPE      | tidb
INSTANCE  | 172.16.5.40:4009
VALUE     |
REFERENCE |
SEVERITY  | critical
DETAILS   | tidb 172.16.5.40:4009 restarted at time '2020/03/26 00:05:45.670'
***************************[ 2. row ]***************************
RULE      | threshold-check
ITEM      | get-token-duration
TYPE      | tidb
INSTANCE  | 172.16.5.40:10089
VALUE     | 0.234
REFERENCE | < 0.001
SEVERITY  | warning
DETAILS   | max duration of 172.16.5.40:10089 tidb get-token-duration is too slow

The following issues can be detected from the diagnostic result above:

  • The first row indicates that the 172.16.5.40:4009 TiDB instance is restarted at 2020/03/26 00:05:45.670.
  • The second row indicates that the maximum get-token-duration time of the 172.16.5.40:10089 TiDB instance is 0.234s, but the expected time is less than 0.001s.

You can also specify conditions, for example, to query the critical level diagnostic results:

select * from information_schema.inspection_result where severity='critical';

Query only the diagnostic result of the critical-error rule:

select * from information_schema.inspection_result where rule='critical-error';

Diagnostic rules

The diagnostic module contains a series of rules. These rules compare the results with the thresholds after querying the existing monitoring tables and cluster information tables. If the results exceed the thresholds, the diagnostics of warning or critical is generated and the corresponding information is provided in the details column.

You can query the existing diagnostic rules by querying the inspection_rules system table:

select * from information_schema.inspection_rules where type='inspection';
+-----------------+------------+---------+
| NAME            | TYPE       | COMMENT |
+-----------------+------------+---------+
| config          | inspection |         |
| version         | inspection |         |
| node-load       | inspection |         |
| critical-error  | inspection |         |
| threshold-check | inspection |         |
+-----------------+------------+---------+

config diagnostic rule

In the config diagnostic rule, the following two diagnostic rules are executed by querying the CLUSTER_CONFIG system table:

  • Check whether the configuration values of the same component are consistent. Not all configuration items has this consistency check. The allowlist of consistency check is as follows:

    // The allowlist of the TiDB configuration consistency check
    port
    status.status-port
    host
    path
    advertise-address
    status.status-port
    log.file.filename
    log.slow-query-file
    tmp-storage-path
    
    // The allowlist of the PD configuration consistency check
    advertise-client-urls
    advertise-peer-urls
    client-urls
    data-dir
    log-file
    log.file.filename
    metric.job
    name
    peer-urls
    
    // The allowlist of the TiKV configuration consistency check
    server.addr
    server.advertise-addr
    server.status-addr
    log-file
    raftstore.raftdb-path
    storage.data-dir
    storage.block-cache.capacity
  • Check whether the values of the following configuration items are as expected.

    ComponentConfiguration itemExpected value
    TiDBlog.slow-thresholdlarger than 0
    TiKVraftstore.sync-logtrue

version diagnostic rule

The version diagnostic rule checks whether the version hash of the same component is consistent by querying the CLUSTER_INFO system table. See the following example:

SELECT * FROM information_schema.inspection_result WHERE rule='version'\G
***************************[ 1. row ]***************************
RULE      | version
ITEM      | git_hash
TYPE      | tidb
INSTANCE  |
VALUE     | inconsistent
REFERENCE | consistent
SEVERITY  | critical
DETAILS   | the cluster has 2 different tidb versions, execute the sql to see more detail: SELECT * FROM information_schema.cluster_info WHERE type='tidb'

critical-error diagnostic rule

In critical-error diagnostic rule, the following two diagnostic rules are executed:

  • Detect whether the cluster has the following errors by querying the related monitoring system tables in the metrics schema:

    ComponentError nameMonitoring tableError description
    TiDBpanic-counttidb_panic_count_total_countPanic occurs in TiDB.
    TiDBbinlog-errortidb_binlog_error_total_countAn error occurs when TiDB writes binlog.
    TiKVcritical-errortikv_critical_error_total_counThe critical error of TiKV.
    TiKVscheduler-is-busytikv_scheduler_is_busy_total_countThe TiKV scheduler is too busy, which makes TiKV temporarily unavailable.
    TiKVcoprocessor-is-busytikv_coprocessor_is_busy_total_countThe TiKV Coprocessor is too busy.
    TiKVchannel-is-fulltikv_channel_full_total_countThe "channel full" error occurs in TiKV.
    TiKVtikv_engine_write_stalltikv_engine_write_stallThe "stall" error occurs in TiKV.
  • Check whether any component is restarted by querying the metrics_schema.up monitoring table and the CLUSTER_LOG system table.

threshold-check diagnostic rule

The threshold-check diagnostic rule checks whether the following metrics in the cluster exceed the threshold by querying the related monitoring system tables in the metrics schema:

ComponentMonitoring metricMonitoring tableExpected valueDescription
TiDBtso-durationpd_tso_wait_duration< 50msThe wait duration of getting the TSO of transaction.
TiDBget-token-durationtidb_get_token_duration< 1msQueries the time it takes to get the token. The related TiDB configuration item is token-limit.
TiDBload-schema-durationtidb_load_schema_duration< 1sThe time it takes for TiDB to update the schema metadata.
TiKVscheduler-cmd-durationtikv_scheduler_command_duration< 0.1sThe time it takes for TiKV to execute the KV cmd request.
TiKVhandle-snapshot-durationtikv_handle_snapshot_duration< 30sThe time it takes for TiKV to handle the snapshot.
TiKVstorage-write-durationtikv_storage_async_request_duration< 0.1sThe write latency of TiKV.
TiKVstorage-snapshot-durationtikv_storage_async_request_duration< 50msThe time it takes for TiKV to get the snapshot.
TiKVrocksdb-write-durationtikv_engine_write_duration< 100msThe write latency of TiKV RocksDB.
TiKVrocksdb-get-durationtikv_engine_max_get_duration< 50msThe read latency of TiKV RocksDB.
TiKVrocksdb-seek-durationtikv_engine_max_seek_duration< 50msThe latency of TiKV RocksDB to execute seek.
TiKVscheduler-pending-cmd-countikv_scheduler_pending_commands< 1000The number of commands stalled in TiKV.
TiKVindex-block-cache-hittikv_block_index_cache_hit> 0.95The hit rate of index block cache in TiKV.
TiKVfilter-block-cache-hittikv_block_filter_cache_hit> 0.95The hit rate of filter block cache in TiKV.
TiKVdata-block-cache-hittikv_block_data_cache_hit> 0.80The hit rate of data block cache in TiKV.
TiKVleader-score-balancepd_scheduler_store_status< 0.05Checks whether the leader score of each TiKV instance is balanced. The expected difference between instances is less than 5%.
TiKVregion-score-balancepd_scheduler_store_status< 0.05Checks whether the Region score of each TiKV instance is balanced. The expected difference between instances is less than 5%.
TiKVstore-available-balancepd_scheduler_store_status< 0.2Checks whether the available storage of each TiKV instance is balanced. The expected difference between instances is less than 20%.
TiKVregion-countpd_scheduler_store_status< 20000Checks the number of Regions on each TiKV instance. The expected number of Regions in a single instance is less than 20,000.
PDregion-healthpd_region_health< 100Detects the number of Regions that are in the process of scheduling in the cluster. The expected number is less than 100 in total.

In addition, this rule also checks whether the CPU usage of the following threads in a TiKV instance is too high:

  • scheduler-worker-cpu
  • coprocessor-normal-cpu
  • coprocessor-high-cpu
  • coprocessor-low-cpu
  • grpc-cpu
  • raftstore-cpu
  • apply-cpu
  • storage-readpool-normal-cpu
  • storage-readpool-high-cpu
  • storage-readpool-low-cpu
  • split-check-cpu

The built-in diagnostic rules are constantly being improved. If you have more diagnostic rules, welcome to create a PR or an issue in the tidb repository.