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(20) unsigned | YES | | NULL | | | User | varchar(64) | YES | | NULL | | | Host | varchar(64) | YES | | NULL | | | Conn_ID | bigint(20) unsigned | YES | | NULL | | | Session_alias | varchar(64) | YES | | NULL | | | Exec_retry_count | bigint(20) 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(20) 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(22) | YES | | NULL | | | Write_size | bigint(22) | YES | | NULL | | | Prewrite_region | bigint(22) | YES | | NULL | | | Txn_retry | bigint(22) | 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(20) unsigned | YES | | NULL | | | Total_keys | bigint(20) unsigned | YES | | NULL | | | Process_keys | bigint(20) unsigned | YES | | NULL | | | Rocksdb_delete_skipped_count | bigint(20) unsigned | YES | | NULL | | | Rocksdb_key_skipped_count | bigint(20) unsigned | YES | | NULL | | | Rocksdb_block_cache_hit_count | bigint(20) unsigned | YES | | NULL | | | Rocksdb_block_read_count | bigint(20) unsigned | YES | | NULL | | | Rocksdb_block_read_byte | bigint(20) 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(20) | YES | | NULL | | | Disk_max | bigint(20) | YES | | NULL | | | KV_total | double | YES | | NULL | | | PD_total | double | YES | | NULL | | | Backoff_total | double | YES | | NULL | | | Write_sql_response_total | double | YES | | NULL | | | Result_rows | bigint(22) | 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 | | | Plan | longtext | YES | | NULL | | | Plan_digest | varchar(128) | YES | | NULL | | | Binary_plan | longtext | YES | | NULL | | | Prev_stmt | longtext | YES | | NULL | | | Query | longtext | YES | | NULL | | +-------------------------------+---------------------+------+------+---------+-------+ 79 rows in set (0.00 sec)

CLUSTER_SLOW_QUERY table

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(20) unsigned | YES | | NULL | | | User | varchar(64) | YES | | NULL | | | Host | varchar(64) | YES | | NULL | | | Conn_ID | bigint(20) unsigned | YES | | NULL | | | Session_alias | varchar(64) | YES | | NULL | | | Exec_retry_count | bigint(20) 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(20) 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(22) | YES | | NULL | | | Write_size | bigint(22) | YES | | NULL | | | Prewrite_region | bigint(22) | YES | | NULL | | | Txn_retry | bigint(22) | 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(20) unsigned | YES | | NULL | | | Total_keys | bigint(20) unsigned | YES | | NULL | | | Process_keys | bigint(20) unsigned | YES | | NULL | | | Rocksdb_delete_skipped_count | bigint(20) unsigned | YES | | NULL | | | Rocksdb_key_skipped_count | bigint(20) unsigned | YES | | NULL | | | Rocksdb_block_cache_hit_count | bigint(20) unsigned | YES | | NULL | | | Rocksdb_block_read_count | bigint(20) unsigned | YES | | NULL | | | Rocksdb_block_read_byte | bigint(20) 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(20) | YES | | NULL | | | Disk_max | bigint(20) | YES | | NULL | | | KV_total | double | YES | | NULL | | | PD_total | double | YES | | NULL | | | Backoff_total | double | YES | | NULL | | | Write_sql_response_total | double | YES | | NULL | | | Result_rows | bigint(22) | 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 | | | Plan | longtext | YES | | NULL | | | Plan_digest | varchar(128) | YES | | NULL | | | Binary_plan | longtext | YES | | NULL | | | Prev_stmt | longtext | YES | | NULL | | | Query | longtext | YES | | NULL | | +-------------------------------+---------------------+------+------+---------+-------+ 80 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;

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