25个并发，每个并发持续执行一个并行度为24的查询sql，在等待事件中 列出了等待时间最长的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.