reads by KTSJ

From: Noveljic Nenad <>
Date: Tue, 12 May 2020 21:02:23 +0000
Message-ID: <>

I started occasionally seeing KTSJ slaves heavily waiting on "free buffer waits" and "db file sequential read" after upgrading from to

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')"

%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,


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Received on Tue May 12 2020 - 23:02:23 CEST

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