Performance Tuning - Question 029

When LGWR signals a checkpoint, what happens in the buffer cache?

A . The server process copies dirty data blocks from the LRU list to the write list, and DBWn writes the data blocks to datafiles.

B . The reading, batching, and writing of dirty data blocks are parallelized.

C. DBWn copies dirty data blocks from the LRU list to the write list and writes the data blocks to datafiles.

D . LGWR copies dirty data blocks from the LRU list to the write list, and the server process writes the data blocks to datafiles.

Explanation:

Answer C: One of the primary functions of the checkpoint is to synchronize dirty blocks in memory with blocks on disk. LGWR signals the checkpoint, and DBWn copies the dirty blocks from the LRU list to the write list, and then writes them to disk. The reading, batching, and writing of dirty blocks is parallelized when we use multiple DBW processes. In 'The server process copies dirty data blocks from the LRU list to the write list, and DBWn writes the data blocks to datafiles' and 'LGWR copies dirty data blocks from the LRU list to the write list, and the server process writes the data blocks to datafiles,' we have obfuscated the responsibilities.