RE: reads by KTSJ
Date: Wed, 13 May 2020 06:35:56 +0000
Message-ID: <21692_1589351773_5EBB955D_21692_11530_1_546c614b8af244eb9f0ae45aa69c691e_at_vontobel.com>
Thanks, Mladen.
I forgot to mention, it isn‘t SQL - v$active_session_history.sql_id is empty for those reads.
Best regards,
Nenad
Von: Mladen Gogala <gogala.mladen_at_gmail.com<mailto:gogala.mladen_at_gmail.com>>
Datum Mittwoch, 13. Mai 2020, 1:11 AM
An: Noveljic Nenad <nenad.noveljic_at_vontobel.com<mailto:nenad.noveljic_at_vontobel.com>>, ORACLE-L (oracle-l_at_freelists.org) <oracle-l_at_freelists.org<mailto:oracle-l_at_freelists.org>>
Betreff: Re: reads by KTSJ
Hi Nenad!
Both Wnnnn and KTSJ slaves are space management processes. Heuristically, I would check whether there is a shortage of space in any of your tablespaces. Other than that, you can try tracing Wnnnn process or KTSJ slave processes using oradebug event. 10046 trace files may give you better insight in what is going on.
Regards
On Tue, 2020-05-12 at 21:02 +0000, Noveljic Nenad wrote: I started occasionally seeing KTSJ slaves heavily waiting on “free buffer waits” and “db file sequential read” after upgrading from 18.7.0.0.190716 to 19.7.0.0.200414:
SQL> _at_ash_wait_chains2 "program2||' '||event2||' '||module||' '||action" "program2 like '(W%'" "to_date('2020-05-12 13:37:15')" "to_date('2020-05-12 14:37:15')"
- Display ASH Wait Chain Signatures script v0.5 BETA by Tanel Poder ( http://blog.tanelpoder.com )
%This SECONDS AAS WAIT_CHAIN FIRST_SEEN LAST_SEEN ------ ---------- ------- ------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------ ------------------- ------------------- 22% 310 .1 -> (Wnnn) free buffer waits KTSJ KTSJ Slave -> (DBWnnn) db file parallel write 2020-05-12 13:46:55 2020-05-12 13:48:40 10% 144 .0 -> (Wnnn) db file sequential read KTSJ KTSJ Slave 2020-05-12 13:46:54 2020-05-12 13:48:52 10% 144 .0 -> (WnnA) free buffer waits KTSJ KTSJ Slave -> (DBWnnn) db file parallel write 2020-05-12 13:46:55 2020-05-12 13:57:13 7% 104 .0 -> (WnnA) db file sequential read KTSJ KTSJ Slave 2020-05-12 13:46:54 2020-05-12 13:57:11
Some of the affected processes have the following entries in the trace file:
- SESSION ID:(1202.8580) 2020-05-12T13:46:54.295884+02:00
- CLIENT ID:() 2020-05-12T13:46:54.295916+02:00
- SERVICE NAME:(SYS$BACKGROUND) 2020-05-12T13:46:54.295947+02:00
- MODULE NAME:(KTSJ) 2020-05-12T13:46:54.295978+02:00
- ACTION NAME:(KTSJ Slave) 2020-05-12T13:46:54.296009+02:00
- CLIENT DRIVER:() 2020-05-12T13:46:54.296039+02:00
[ktspsc_segmon] submitted segfix task [ktspsc_segmon] submitted segfix task [ktspsc_segmon] submitted segfix task
The tablespaces are autoextensible, but I don’t know if they were extended during this time period. The IO performance is OK.
I examined one of the read bloccks – it belongs to a user schema, nothing special about it:
How to figure out what might have caused this KTSJ slave activity?
Best regards,
Nenad
https://nenadnoveljic.com/blog/
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-- Mladen Gogala Database Consultant Tel: (347) 321-1217 Email:gogala.mladen_at_gmail.comReceived on Wed May 13 2020 - 08:35:56 CEST
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