在測試資料庫的awr報告中發現大量的 dfs lock handle，引出這個文件作為參考
25個併發，每個併發持續執行一個並行度為24的查詢sql，在等待事件中列出了等待時間最長的dfs lock handle

APPLIES TO:

Oracle Database - Enterprise Edition - Version 11.1.0.6 to 12.1.0.2B1 [Release 11.1 to 12.1]
Information in this document applies to any platform.

SYMPTOMS

Queries running slow with high waits for 'latch: query server process' and 'DFS lock handle'

Top 10 Foreground Events by Total Wait Time

Event	Waits	Total Wait Time (sec)	Wait Avg(ms)	% DB time	Wait Class
DFS lock handle	1,336	29.4K	22043	52.3	Other
latch free	6,200	25.7K	4137	45.5	Other
DB CPU		463.3		.8

Latch Activity

Latch Name	Get Requests	Pct Get Miss	Avg Slps /Miss	Wait Time (s)	NoWait Requests	Pct NoWait Miss

query server process

80,297

4.01

2.68

25830

2,104

0.29

CHANGES

Table or index degree of parallelism has been altered.

CAUSE

Highly concurrent queries that normally take a fraction of a second to run started executing with a high degree or parallelism.

This leads to extreme contention for the 'latch: query server process' when spawning and cleaning up detached processes.

SOLUTION

Do not run highly concurrent queries in parallel.

high wait for