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High Buffer busy waits during log switches (Doc ID 1577905.1)

Last updated on FEBRUARY 01, 2022

Applies to:

Oracle Database - Enterprise Edition - Version to [Release 10.2 to 11.2]
Oracle Database Cloud Schema Service - Version N/A and later
Gen 1 Exadata Cloud at Customer (Oracle Exadata Database Cloud Machine) - Version N/A and later
Oracle Cloud Infrastructure - Database Service - Version N/A and later
Oracle Database Exadata Express Cloud Service - Version N/A and later
Information in this document applies to any platform.


NOTE: In the images and/or the document content below, the user information and data used represents fictitious data from the Oracle sample schema(s) or Public Documentation delivered with an Oracle database product. Any similarity to actual persons, living or dead, is purely coincidental and not intended in any manner. 

When the log switches happen the instance experiences High buffer busy waits for DML transactions. 

AWR report shows the sudden Buffer Busy waits spiking up
Top 5 Timed Foreground Events
Event                           Waits            Time(s)                         Avg wait (ms)          % DB time  Wait Class
db file sequential read  1,214,478       4,843                                 4                      37.27       User I/O
DB CPU                       2,581                                                                              19.87 
buffer busy waits          598                1,552                                 2596                 11.95       Concurrency
direct path read temp   98,197            651                                    7                      5.01         User I/O
log file sync                 26,889            147                                    5                      1.13         Commit


ASH Reports shows High Buffer Busy waits on DML statements.
Top SQL with Top Events
SQL ID             % Event Top                                   Row Source                                          % RwSrc                 SQL Text 
zzzzzzzzzzzz    buffer busy waits 3.13               ** Row Source Not Available **               3.13                       INSERT INTO TABLE_xxxxx (O... 
zzzzzzzzzzzz    enq: TX - index contention 1.01 ** Row Source Not Available **               1.01                       INSERT INTO xxxxxxx (O... 
wwwwwwww   buffer busy waits 2.64              ** Row Source Not Available **               2.64                       INSERT INTO TABLE_wwwwww(O...


The manual log switches "alter system archive log current" or implicit log switch can cause this high buffer busy waits spike.



The instance uses a product called 'SafeNet Luna' for their HSM which is a key store for external TDE module for the tablespace encryption.  

Safenet is configured for HA, which means that one of the 'Safenet Servers' is actually at a remote WAN-Based location - so depending on availability of the local Safenet server, a request may be redirected to go over the WAN.


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