Thank you Jonathan and Tanel for your invaluable inputs – learned so much from
them.
Find my answers below:
- It isn’t CTAS – last_ddl_time is from long time ago.
- I haven’t seen any “buffer busy waits”. It was “free buffer waits”
instead – block class is not shown with event2 for them.
- I’ll setup the short stacks with wait events and wait for the next
occurrence.
Best regards,
Nenad
https://nenadnoveljic.com/blog
From: oracle-l-bounce@xxxxxxxxxxxxx <oracle-l-bounce@xxxxxxxxxxxxx> On Behalf
Of Jonathan Lewis
Sent: Mittwoch, 13. Mai 2020 21:06
To: ORACLE-L (oracle-l@xxxxxxxxxxxxx) <oracle-l@xxxxxxxxxxxxx>
Subject: Re: reads by KTSJ
This seg fix state is what made me think it might be related to the fix-ups
that take place on space allocation from parallel CTAS where every slave
creates its own segment and the QC then has to clean-out the blocks that were
initially segment header and space management blocks as it combines the
separate segments into a single one.
Regards
Jonathan Lewis
On Wed, May 13, 2020 at 7:17 PM Tanel Poder
<tanel@xxxxxxxxxxxxxx<mailto:tanel@xxxxxxxxxxxxxx>> wrote:
You mentioned that there were some buffer busy waits showing up too?
Instead of relying on the block address & DBA_EXTENTS query (maybe this block
has been reused by something else by now?), you can use ashtop to see which
block class the buffer busy waits were against. A random example from my lab:
SQL> @ash/dashtop event2 "event='buffer busy waits'" sysdate-90 sysdate
Total
Seconds AAS %This EVENT2
--------- ------- ------- ---------------------------------------------
38360 .0 88% buffer busy waits [data block]
4680 .0 11% buffer busy waits [undo data]
540 .0 1% buffer busy waits [undo header]
130 .0 0% buffer busy waits [file header block]
Also the [ktspsc_segmon] submitted segfix task messages in your tracefiles are
interesting.
SQL> SELECT description FROM x$ktsjtaskclass ORDER BY 1;
DESCRIPTION
----------------------------------------------------------------
AIM scheduler
Affinitize segment for IM Hash Index
CLISLAVE
DROPTEMP
...
SEG DICT UPDATE
SYSAUX FILE OFFLINE CHECK
SYSAUX FILE ONLINE CHECK
Segment Fixstate
Segment Monitor
...
Indeed there's a KTSJ task class called "Segment Fixstate", so maybe Oracle's
autonomously fixing something under the hood :)
--
Tanel
https://tanelpoder.com
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