Database Reference
In-Depth Information
When we place tablespace offline.
When we drop or truncate table.
When we change the tablespace to read only.
Whenever the threshold mark of free buffers reaches. It's the
mark when the quantity of free buffers in database buffer cache
drops to a certain level.
LGWR
Like I said before, redo log files gets written by Log Writer
process (LGWR) in a circular fashion i.e. when a Log Writer
process finishes writing the last redo log file, it will start writing
or rather overwriting the first one. Whenever the Log Writer
process switches from one file to another, “Log Switch”
happens. When Log Switch happens, checkpoint happens, when
checkpoint happens, DBWn writes the dirty buffers to the data
files. The Log Writer process writes the “Redo Log Buffers”
from the Redo Log Cache to the Redo Log files under following
circumstances or events.
Whenever we issue COMMIT statement to complete the
transaction.
Every three seconds
LGWR writes to all the Redo Log members or mirror images
simultaneously even if one of the member is damaged, LGWR
will continue to write on the good ones.
ARCn
If we don't want the Redo Log files to be overwritten by LGWR
process then we have to run the database in ARCHIVELOG
mode and we have to enable automatic archiving by setting
LOG_ARCHIVE_START = True.
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