Regarding Checkpoint & Dirty Buffers

[adewri]

Hi

Dirty Buffers are written to disk only under two circumstances.

1. When an Oracle process requests data, it searches the data in the buffer cache, and if it finds data, the result is a cache hit. If it cannot find the data, the result is a cache miss, and data then needs to be copied from disk to the buffer.Before reading a data block into the cache, the process must first find a free buffer. The server process on behalf of the user process searches either until it finds a free buffer or until it has searched the threshold limit of buffers. If the server process finds a dirty buffer as it searches the LRU list, it moves that buffer to the write list and continues to search. If an Oracle server process searches the threshold limit of buffers without finding a free buffer, the process stops searching and signals the DBWn background process to write some of the dirty buffers to disk.

2. When a checkpoint occurs. Checkpoints help to reduce the time required for instance recovery. A checkpoint is an event that flushes the modified data from the buffer cache to the disk and updates the control file and data files. The checkpoint process (CKPT) updates the headers of data files and control files; the actual blocks
are written to the file by the DBWn process.

Checkpoint occurs when log switch takes place. or depending on the values of LOG_CHECKPOINT_INTERVAL(blocks) and LOG_CHECKPOINT_TIMEOUT(seconds).

So you can say during checkpoint, dirty buffers are written to the disk.

Hope this helps

Regards
Amar

Oops! i need to increase my typing speed :-)