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SLOW_QUERY

SLOW_QUERY 表提供当前节点的慢查询信息,这些信息是 TiDB 慢日志文件 的解析结果。表中的列名与慢日志中的字段名一一对应。

USE INFORMATION_SCHEMA; DESC SLOW_QUERY;

输出如下:

+-------------------------------+---------------------+------+------+---------+-------+ | 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 | | | 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 | | +-------------------------------+---------------------+------+------+---------+-------+ 81 rows in set (0.00 sec)

Query 列的最大语句长度受 tidb_stmt_summary_max_sql_length 系统变量限制。

CLUSTER_SLOW_QUERY 表

CLUSTER_SLOW_QUERY 表提供整个集群所有节点的慢查询信息,这些信息是 TiDB 慢日志文件的解析结果。你可以像使用 SLOW_QUERY 表一样使用 CLUSTER_SLOW_QUERY 表。CLUSTER_SLOW_QUERY 表的表结构与 SLOW_QUERY 表的区别在于多了一个 INSTANCE 列。INSTANCE 列表示该慢查询信息所在的 TiDB 节点地址。

DESC CLUSTER_SLOW_QUERY;

输出如下:

+-------------------------------+---------------------+------+------+---------+-------+ | 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 | | | 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 | | +-------------------------------+---------------------+------+------+---------+-------+ 82 rows in set (0.00 sec)

当查询集群系统表时,TiDB 并不会从所有节点拉取数据,而是将相关计算下推到其他节点。执行计划如下:

DESC SELECT COUNT(*) FROM CLUSTER_SLOW_QUERY WHERE user = 'u1';

输出如下:

+----------------------------+----------+-----------+--------------------------+------------------------------------------------------+ | 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)

在上述执行计划中,user = u1 条件被下推到其他(cop)TiDB 节点,聚合算子也被下推(图中的 StreamAgg 算子)。

目前,由于系统表没有收集统计信息,有时某些聚合算子无法下推,导致执行较慢。此时,你可以手动指定 SQL HINT,将聚合算子下推。例如:

SELECT /*+ AGG_TO_COP() */ COUNT(*) FROM CLUSTER_SLOW_QUERY GROUP BY user;

查看执行信息

通过在 SLOW_QUERY 表上执行 EXPLAIN ANALYZE 查询,你可以获得数据库获取慢查询信息的详细过程信息。但在 CLUSTER_SLOW_QUERY 表上执行 EXPLAIN ANALYZE不会返回这些信息。

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)

在输出结果中,可以关注 execution info 部分的以下字段(为便于阅读已格式化):

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
字段说明
initialize初始化耗时
read_file读取慢日志文件耗时
parse_log.time解析慢日志文件耗时
parse_log.concurrency解析慢日志文件的并发度(由 tidb_distsql_scan_concurrency 设置)
total_file慢日志文件总数
read_file实际读取的慢日志文件数
read_size从日志文件读取的字节数

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