- 【TiDB 版本】：v3.0.9
- 【问题描述】：偶发性慢查询，通过查看slow_query表的时候为
Time: 2020-06-01 07:44:00.159650
Txn_start_ts: 417062881915306181
User:
Host:
Conn_ID: 590035
Query_time: 4.905505229
Parse_time: 0.000037627
Compile_time: 0.00015489
Prewrite_time: 4.902307495
Binlog_prewrite_time: 4.902309825
Commit_time: 0
Get_commit_ts_time: 0
Commit_backoff_time: 7.1370000000000005
Backoff_types: [txnLock
Resolve_lock_time: 0.000012073
Local_latch_wait_time: 0
Write_keys: 3
Write_size: 874
Prewrite_region: 4
Txn_retry: 0
Process_time: 0
Wait_time: 0
Backoff_time: 0
LockKeys_time: 0
Request_count: 2
Total_keys: 0
Process_keys: 0
DB:
Index_names: [tablename:uq_task_id]
Is_internal: 0
Digest: ebbf14e061e5ddb64f55ba0409485568349842587632cb235ebdee2f75a97e73
Stats: tablename:417062881508982869
Cop_proc_avg: 0
Cop_proc_p90: 0
Cop_proc_max: 0
Cop_proc_addr:
Cop_wait_avg: 0
Cop_wait_p90: 0
Cop_wait_max: 0
Cop_wait_addr:
Mem_max: 23268
Succ: 1
Plan: IndexLookUp_7 root 0.013917095401448197
├─IndexScan_4 cop 0.9928382343232485 table:tablename, index:task_id, range:[504922951218127054,504922951218127054], keep order:false
└─Selection_6 cop 0.013917095401448197 eq(table_name.status, 1)
└─TableScan_5 cop 0.9928382343232485 table:table_name, keep order:false
Plan_digest: daf62da201fd6270270faedd17e1a901e71ac3853e4b04ecf10ad4862b790b5b
Prev_stmt:
Query: update tablename set a = 140951, b=2 where task_id IN ( 1411421
) and b = b;`
task_id为唯一索引，平时执行很快基本上不到100ms，请问这种情况一般是什么原因导致的。