DBA Sensation

June 9, 2010

Sth. about checkpoint

Filed under: 1. Oracle, [System Performance tuning] — Tags: , , — zhefeng @ 2:31 pm

reading a article about checkpoint on metalink(Checkpoint Tuning and Troubleshooting Guide [ID 147468.1])

Here are some good points for checkpoint:

Oracle writes the dirty buffers to disk only on certain conditions:
– A shadow process must scan more than one-quarter of the db_block_buffer
parameter.
– Every three seconds.
– When a checkpoint is produced.

A checkpoint is realized on five types of events:
– At each switch of the redo log files.
– When the delay for LOG_CHECKPOINT_TIMEOUT is reached.
– When the size in bytes corresponding to :
(LOG_CHECKPOINT_INTERVAL* size of IO OS blocks)
is written on the current redo log file.
– Directly by the ALTER SYSTEM SWITCH LOGFILE command.
– Directly with the ALTER SYSTEM CHECKPOINT command.

During a checkpoint the following occurs:
– The database writer (DBWR) writes all modified database
blocks in the buffer cache back to datafiles,
– Checkpoint process (ckpt) updates the headers of all
the datafiles to indicate when the last checkpoint
occurred (SCN)

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