File Extension Messages are seen in alert log.There was no explicit file resize DDL as well.
Resize operation completed for file# 45, old size 26M, new size 28M
Resize operation completed for file# 45, old size 28M, new size 30M
Resize operation completed for file# 45, old size 30M, new size 32M
Resize operation completed for file# 36, old size 24M, new size 26M
In a busy system with lots of DML (insert/update/delete),the alert log could be flooded with many such file extension messages.
CHANGES
CAUSE
These file extension messages were result of diagnostic enhancement through unpublished to record automatic datafile resize operations in the alert log with a message of the form:
"File NN has auto extended from x bytes to y bytes"
This can be useful when diagnosing problems which may be impacted by a file resize.
SOLUTION
In busy systems, the alert log could be completely flooded with file extension messages. A new Hidden parameter parameter "_disable_file_resize_logging" has been introduced through bug 18603375 to stop these messages getting logged into alert log.
(Unpublished) Bug 18603375 - EXCESSIVE FILE EXTENSION MESSAGE IN ALERT LOG
Set the below parameter along with the fix.
SQL> alter system set "_disable_file_resize_logging"=TRUE ; (Its default value is FALSE)
The bug fix 18603375 is included in 12.1.0.2 onwards.