enq: KO - fast object checkpoint 等待事件与 direct path read - 1

最新推荐文章于 2025-07-09 21:58:09 发布

转载最新推荐文章于 2025-07-09 21:58:09 发布 · 454 阅读

在Exadata系统上的Oracle11g数据库运行特定程序时遇到性能瓶颈，具体表现为某一SQL语句执行停滞，并伴随大量enq: KO-fast object checkpoint等待事件。本文探讨了此现象的原因及解决方法。

在Exadata系统上Oracle11g 数据库中执行某个调度procedure Job_SP_DWR_AR_COLLECTION_WEEKLY_P 时，发现卡在某个SQL : 5jctyad1z1s6a 执行不下去，同时出现大量的 enq: KO - fast object checkpoint 等待事件。

1. 查询文档 enq: KO - fast object checkpoint

You see this event because object level checkpoint which happens when you run direct path reads on a segment (like with serial direct read full table scan or parallel execution full segment scans).

KO enqueue - fast object checkpoint means that your session has sent CKPT process a message with instruction to do object level checkpoint and is waiting for a reply.

CKPT in turn asks DBWR process to perform the checkpoint and may wait for response.

So you should check what the DBWR and CKPT processes are doing - whether they're stuck waiting for something (such controlfile enqueue) or doing IO or completely idle.
This you can do using v$session_wait or v$session_event...

You can run this:
select sid,program from v$session where program like '%CKPT%' or program like '%DBW%';
and then run
select sid,event,state,p1,p2,p3,seconds_in_wait from v$session_wait where sid in
(select sid from v$session where program like '%CKPT%' or program like '%DBW%');

----
fast object checkpoint can be disabled by setting
"_db_fast_obj_ckpt"=false".
What is the impact to parallel scans with this setting? Any other adverse impact from setting this parameter?

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