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;
+---------------------------+---------------------+------+------+---------+-------+ | Field | Type | Null | Key | Default | Extra | +---------------------------+---------------------+------+------+---------+-------+ | Time | timestamp(6) | YES | | 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 | | | 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 | | | 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 | | | Succ | tinyint(1) | YES | | NULL | | | Plan_from_cache | tinyint(1) | YES | | NULL | | | Plan | longblob | YES | | NULL | | | Plan_digest | varchar(128) | YES | | NULL | | | Prev_stmt | longblob | YES | | NULL | | | Query | longblob | YES | | NULL | | +---------------------------+---------------------+------+------+---------+-------+ 54 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;
+---------------------------+---------------------+------+------+---------+-------+ | Field | Type | Null | Key | Default | Extra | +---------------------------+---------------------+------+------+---------+-------+ | INSTANCE | varchar(64) | YES | | NULL | | | Time | timestamp(6) | YES | | 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 | | | 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 | | | 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 | | | Succ | tinyint(1) | YES | | NULL | | | Plan_from_cache | tinyint(1) | YES | | NULL | | | Plan | longblob | YES | | NULL | | | Plan_digest | varchar(128) | YES | | NULL | | | Prev_stmt | longblob | YES | | NULL | | | Query | longblob | YES | | NULL | | +---------------------------+---------------------+------+------+---------+-------+ 55 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';
+--------------------------+----------+-----------+--------------------------+------------------------------------------------------+ | id | estRows | task | access object | operator info | +--------------------------+----------+-----------+--------------------------+------------------------------------------------------+ | StreamAgg_20 | 1.00 | root | | funcs:count(Column#53)->Column#51 | | └─TableReader_21 | 1.00 | root | | data:StreamAgg_9 | | └─StreamAgg_9 | 1.00 | cop[tidb] | | funcs:count(1)->Column#53 | | └─Selection_19 | 10.00 | cop[tidb] | | eq(information_schema.cluster_slow_query.user, "u1") | | └─TableFullScan_18 | 10000.00 | cop[tidb] | table:CLUSTER_SLOW_QUERY | keep order:false, stats:pseudo | +--------------------------+----------+-----------+--------------------------+------------------------------------------------------+

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(即图中的 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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