| title | summary |
|---|---|
SLOW_QUERY |
了解 INFORMATION_SCHEMA 表 `SLOW_QUERY`。 |
SLOW_QUERY 表中提供了当前节点的慢查询相关的信息，其内容通过解析当前节点的 TiDB 慢查询日志而来，列名和慢日志中的字段名是一一对应。关于如何使用该表调查和改善慢查询，请参考慢查询日志文档。
USE INFORMATION_SCHEMA;
DESC slow_query;输出结果示例如下：
+--------------------------------------------+-----------------+------+------+---------+-------+
| Field | Type | Null | Key | Default | Extra |
+--------------------------------------------+-----------------+------+------+---------+-------+
| Time | timestamp(6) | NO | PRI | NULL | |
| Txn_start_ts | bigint unsigned | YES | | NULL | |
| User | varchar(64) | YES | | NULL | |
| Host | varchar(64) | YES | | NULL | |
| Conn_ID | bigint unsigned | YES | | NULL | |
| Session_alias | varchar(64) | YES | | NULL | |
| Exec_retry_count | bigint unsigned | YES | | NULL | |
| Exec_retry_time | double | YES | | NULL | |
| Query_time | double | YES | | NULL | |
| Parse_time | double | YES | | NULL | |
| Compile_time | double | YES | | NULL | |
| Rewrite_time | double | YES | | NULL | |
| Preproc_subqueries | bigint unsigned | YES | | NULL | |
| Preproc_subqueries_time | double | YES | | NULL | |
| Optimize_time | double | YES | | NULL | |
| Wait_TS | double | YES | | NULL | |
| Prewrite_time | double | YES | | NULL | |
| Wait_prewrite_binlog_time | double | YES | | NULL | |
| Commit_time | double | YES | | NULL | |
| Get_commit_ts_time | double | YES | | NULL | |
| Commit_backoff_time | double | YES | | NULL | |
| Backoff_types | varchar(64) | YES | | NULL | |
| Resolve_lock_time | double | YES | | NULL | |
| Local_latch_wait_time | double | YES | | NULL | |
| Write_keys | bigint | YES | | NULL | |
| Write_size | bigint | YES | | NULL | |
| Prewrite_region | bigint | YES | | NULL | |
| Txn_retry | bigint | YES | | NULL | |
| Cop_time | double | YES | | NULL | |
| Process_time | double | YES | | NULL | |
| Wait_time | double | YES | | NULL | |
| Backoff_time | double | YES | | NULL | |
| LockKeys_time | double | YES | | NULL | |
| Request_count | bigint unsigned | YES | | NULL | |
| Total_keys | bigint unsigned | YES | | NULL | |
| Process_keys | bigint unsigned | YES | | NULL | |
| Rocksdb_delete_skipped_count | bigint unsigned | YES | | NULL | |
| Rocksdb_key_skipped_count | bigint unsigned | YES | | NULL | |
| Rocksdb_block_cache_hit_count | bigint unsigned | YES | | NULL | |
| Rocksdb_block_read_count | bigint unsigned | YES | | NULL | |
| Rocksdb_block_read_byte | bigint unsigned | YES | | NULL | |
| DB | varchar(64) | YES | | NULL | |
| Index_names | varchar(100) | YES | | NULL | |
| Is_internal | tinyint(1) | YES | | NULL | |
| Digest | varchar(64) | YES | | NULL | |
| Stats | varchar(512) | YES | | NULL | |
| Cop_proc_avg | double | YES | | NULL | |
| Cop_proc_p90 | double | YES | | NULL | |
| Cop_proc_max | double | YES | | NULL | |
| Cop_proc_addr | varchar(64) | YES | | NULL | |
| Cop_wait_avg | double | YES | | NULL | |
| Cop_wait_p90 | double | YES | | NULL | |
| Cop_wait_max | double | YES | | NULL | |
| Cop_wait_addr | varchar(64) | YES | | NULL | |
| Mem_max | bigint | YES | | NULL | |
| Disk_max | bigint | YES | | NULL | |
| KV_total | double | YES | | NULL | |
| PD_total | double | YES | | NULL | |
| Backoff_total | double | YES | | NULL | |
| Unpacked_bytes_sent_tikv_total | bigint | YES | | NULL | |
| Unpacked_bytes_received_tikv_total | bigint | YES | | NULL | |
| Unpacked_bytes_sent_tikv_cross_zone | bigint | YES | | NULL | |
| Unpacked_bytes_received_tikv_cross_zone | bigint | YES | | NULL | |
| Unpacked_bytes_sent_tiflash_total | bigint | YES | | NULL | |
| Unpacked_bytes_received_tiflash_total | bigint | YES | | NULL | |
| Unpacked_bytes_sent_tiflash_cross_zone | bigint | YES | | NULL | |
| Unpacked_bytes_received_tiflash_cross_zone | bigint | YES | | NULL | |
| Write_sql_response_total | double | YES | | NULL | |
| Result_rows | bigint | YES | | NULL | |
| Warnings | longtext | YES | | NULL | |
| Backoff_Detail | varchar(4096) | YES | | NULL | |
| Prepared | tinyint(1) | YES | | NULL | |
| Succ | tinyint(1) | YES | | NULL | |
| IsExplicitTxn | tinyint(1) | YES | | NULL | |
| IsWriteCacheTable | tinyint(1) | YES | | NULL | |
| Plan_from_cache | tinyint(1) | YES | | NULL | |
| Plan_from_binding | tinyint(1) | YES | | NULL | |
| Has_more_results | tinyint(1) | YES | | NULL | |
| Resource_group | varchar(64) | YES | | NULL | |
| Request_unit_read | double | YES | | NULL | |
| Request_unit_write | double | YES | | NULL | |
| Time_queued_by_rc | double | YES | | NULL | |
| Tidb_cpu_time | double | YES | | NULL | |
| Tikv_cpu_time | double | YES | | NULL | |
| Plan | longtext | YES | | NULL | |
| Plan_digest | varchar(128) | YES | | NULL | |
| Binary_plan | longtext | YES | | NULL | |
| Prev_stmt | longtext | YES | | NULL | |
| Query | longtext | YES | | NULL | |
+--------------------------------------------+-----------------+------+------+---------+-------+
89 rows in set (0.00 sec)CLUSTER_SLOW_QUERY 表中提供了集群所有节点的慢查询相关的信息，其内容通过解析 TiDB 慢查询日志而来，该表使用上和 SLOW_QUERY 表一样。CLUSTER_SLOW_QUERY 表结构上比 SLOW_QUERY 多一列 INSTANCE，表示该行慢查询信息来自的 TiDB 节点地址。关于如何使用该表调查和改善慢查询，请参考慢查询日志文档。
DESC CLUSTER_SLOW_QUERY;输出结果示例如下：
+--------------------------------------------+-----------------+------+------+---------+-------+
| Field | Type | Null | Key | Default | Extra |
+--------------------------------------------+-----------------+------+------+---------+-------+
| INSTANCE | varchar(64) | YES | | NULL | |
| Time | timestamp(6) | NO | PRI | NULL | |
| Txn_start_ts | bigint unsigned | YES | | NULL | |
| User | varchar(64) | YES | | NULL | |
| Host | varchar(64) | YES | | NULL | |
| Conn_ID | bigint unsigned | YES | | NULL | |
| Session_alias | varchar(64) | YES | | NULL | |
| Exec_retry_count | bigint unsigned | YES | | NULL | |
| Exec_retry_time | double | YES | | NULL | |
| Query_time | double | YES | | NULL | |
| Parse_time | double | YES | | NULL | |
| Compile_time | double | YES | | NULL | |
| Rewrite_time | double | YES | | NULL | |
| Preproc_subqueries | bigint unsigned | YES | | NULL | |
| Preproc_subqueries_time | double | YES | | NULL | |
| Optimize_time | double | YES | | NULL | |
| Wait_TS | double | YES | | NULL | |
| Prewrite_time | double | YES | | NULL | |
| Wait_prewrite_binlog_time | double | YES | | NULL | |
| Commit_time | double | YES | | NULL | |
| Get_commit_ts_time | double | YES | | NULL | |
| Commit_backoff_time | double | YES | | NULL | |
| Backoff_types | varchar(64) | YES | | NULL | |
| Resolve_lock_time | double | YES | | NULL | |
| Local_latch_wait_time | double | YES | | NULL | |
| Write_keys | bigint | YES | | NULL | |
| Write_size | bigint | YES | | NULL | |
| Prewrite_region | bigint | YES | | NULL | |
| Txn_retry | bigint | YES | | NULL | |
| Cop_time | double | YES | | NULL | |
| Process_time | double | YES | | NULL | |
| Wait_time | double | YES | | NULL | |
| Backoff_time | double | YES | | NULL | |
| LockKeys_time | double | YES | | NULL | |
| Request_count | bigint unsigned | YES | | NULL | |
| Total_keys | bigint unsigned | YES | | NULL | |
| Process_keys | bigint unsigned | YES | | NULL | |
| Rocksdb_delete_skipped_count | bigint unsigned | YES | | NULL | |
| Rocksdb_key_skipped_count | bigint unsigned | YES | | NULL | |
| Rocksdb_block_cache_hit_count | bigint unsigned | YES | | NULL | |
| Rocksdb_block_read_count | bigint unsigned | YES | | NULL | |
| Rocksdb_block_read_byte | bigint unsigned | YES | | NULL | |
| DB | varchar(64) | YES | | NULL | |
| Index_names | varchar(100) | YES | | NULL | |
| Is_internal | tinyint(1) | YES | | NULL | |
| Digest | varchar(64) | YES | | NULL | |
| Stats | varchar(512) | YES | | NULL | |
| Cop_proc_avg | double | YES | | NULL | |
| Cop_proc_p90 | double | YES | | NULL | |
| Cop_proc_max | double | YES | | NULL | |
| Cop_proc_addr | varchar(64) | YES | | NULL | |
| Cop_wait_avg | double | YES | | NULL | |
| Cop_wait_p90 | double | YES | | NULL | |
| Cop_wait_max | double | YES | | NULL | |
| Cop_wait_addr | varchar(64) | YES | | NULL | |
| Mem_max | bigint | YES | | NULL | |
| Disk_max | bigint | YES | | NULL | |
| KV_total | double | YES | | NULL | |
| PD_total | double | YES | | NULL | |
| Backoff_total | double | YES | | NULL | |
| Unpacked_bytes_sent_tikv_total | bigint | YES | | NULL | |
| Unpacked_bytes_received_tikv_total | bigint | YES | | NULL | |
| Unpacked_bytes_sent_tikv_cross_zone | bigint | YES | | NULL | |
| Unpacked_bytes_received_tikv_cross_zone | bigint | YES | | NULL | |
| Unpacked_bytes_sent_tiflash_total | bigint | YES | | NULL | |
| Unpacked_bytes_received_tiflash_total | bigint | YES | | NULL | |
| Unpacked_bytes_sent_tiflash_cross_zone | bigint | YES | | NULL | |
| Unpacked_bytes_received_tiflash_cross_zone | bigint | YES | | NULL | |
| Write_sql_response_total | double | YES | | NULL | |
| Result_rows | bigint | YES | | NULL | |
| Warnings | longtext | YES | | NULL | |
| Backoff_Detail | varchar(4096) | YES | | NULL | |
| Prepared | tinyint(1) | YES | | NULL | |
| Succ | tinyint(1) | YES | | NULL | |
| IsExplicitTxn | tinyint(1) | YES | | NULL | |
| IsWriteCacheTable | tinyint(1) | YES | | NULL | |
| Plan_from_cache | tinyint(1) | YES | | NULL | |
| Plan_from_binding | tinyint(1) | YES | | NULL | |
| Has_more_results | tinyint(1) | YES | | NULL | |
| Resource_group | varchar(64) | YES | | NULL | |
| Request_unit_read | double | YES | | NULL | |
| Request_unit_write | double | YES | | NULL | |
| Time_queued_by_rc | double | YES | | NULL | |
| Tidb_cpu_time | double | YES | | NULL | |
| Tikv_cpu_time | double | YES | | NULL | |
| Plan | longtext | YES | | NULL | |
| Plan_digest | varchar(128) | YES | | NULL | |
| Binary_plan | longtext | YES | | NULL | |
| Prev_stmt | longtext | YES | | NULL | |
| Query | longtext | YES | | NULL | |
+--------------------------------------------+-----------------+------+------+---------+-------+
90 rows in set (0.00 sec)查询集群系统表时，TiDB 也会将相关计算下推给其他节点执行，而不是把所有节点的数据都取回来，可以查看执行计划，如下：
DESC SELECT COUNT(*) FROM CLUSTER_SLOW_QUERY WHERE user = 'u1';输出结果示例如下：
+----------------------------+----------+-----------+--------------------------+------------------------------------------------------+
| id | estRows | task | access object | operator info |
+----------------------------+----------+-----------+--------------------------+------------------------------------------------------+
| StreamAgg_7 | 1.00 | root | | funcs:count(1)->Column#75 |
| └─TableReader_13 | 10.00 | root | | data:Selection_12 |
| └─Selection_12 | 10.00 | cop[tidb] | | eq(INFORMATION_SCHEMA.cluster_slow_query.user, "u1") |
| └─TableFullScan_11 | 10000.00 | cop[tidb] | table:CLUSTER_SLOW_QUERY | keep order:false, stats:pseudo |
+----------------------------+----------+-----------+--------------------------+------------------------------------------------------+
4 rows in set (0.00 sec)上面执行计划表示，会将 user = u1 条件下推给其他的 (cop) TiDB 节点执行，也会把聚合算子（即上面输出结果中的 StreamAgg 算子）下推。
目前由于没有对系统表收集统计信息，所以有时会导致某些聚合算子不能下推，导致执行较慢，用户可以通过手动指定聚合下推的 SQL HINT 来将聚合算子下推，示例如下：
SELECT /*+ AGG_TO_COP() */ COUNT(*) FROM CLUSTER_SLOW_QUERY GROUP BY user;通过对 SLOW_QUERY 表执行 EXPLAIN ANALYZE，你可以获取数据库如何检索慢查询信息的详情。然而，如果对 CLUSTER_SLOW_QUERY 表执行 EXPLAIN ANALYZE，将无法获取这些信息。
示例：
EXPLAIN ANALYZE SELECT * FROM INFORMATION_SCHEMA.SLOW_QUERY LIMIT 1\G*************************** 1. row ***************************
id: Limit_7
estRows: 1.00
actRows: 1
task: root
access object:
execution info: time:3.46ms, loops:2, RU:0.000000
operator info: offset:0, count:1
memory: N/A
disk: N/A
*************************** 2. row ***************************
id: └─MemTableScan_10
estRows: 10000.00
actRows: 64
task: root
access object: table:SLOW_QUERY
execution info: time:3.45ms, loops:1, initialize: 55.5µs, read_file: 1.21ms, parse_log: {time:4.11ms, concurrency:15}, total_file: 1, read_file: 1, read_size: 4.06 MB
operator info: only search in the current 'tidb-slow.log' file
memory: 1.26 MB
disk: N/A
2 rows in set (0.01 sec)
在输出中，查看 execution info 中的以下字段（为便于阅读，这些字段的格式已优化）：
initialize: 55.5µs,
read_file: 1.21ms,
parse_log: {
time:4.11ms,
concurrency:15
},
total_file: 1,
read_file: 1,
read_size: 4.06 MB
| 字段 | 描述 |
|---|---|
initialize |
用于初始化的时间 |
read_file |
用于读取慢日志文件的时间 |
parse_log.time |
用于解析慢日志文件的时间 |
parse_log.concurrency |
解析慢日志文件的并发度（由 tidb_distsql_scan_concurrency 控制） |
total_file |
慢日志文件的总数 |
read_file |
已读取的慢日志文件数 |
read_size |
从日志文件中读取的字节数 |