本文探讨了数据库检查点（Checkpoint）的概念，特别是在Oracle数据库中Checkpoint进程（CKPT）的作用。CKPT进程负责更新控制文件和数据文件头中的检查点信息，并在特定情况下触发，如使表空间变为只读或离线状态。当CKPT进程启动时，它会将修改过的数据块写入数据文件，而不是重做日志文件或其他文件。
QUESTION 238
In the instance of the PROD database, the checkpoint (CKPT) process runs after every minute. A database user updates the rows of the ORDERS table. Because of the configuration, the CKPT process gets initiated before the user commits the transaction.
What would happen to the modified blocks when the CKPT process is started?
A. The modified blocks would be written to the data files.
B. The modified blocks would be written to the temp files.
C. The modified blocks would be written to the control file.
D. The modified blocks would be written to the redo log files.
E. The modified blocks would be written to the archived redo log files.
F. The modified blocks would be retained in the database buffer cache.
Answer: A
Checkpoint Process (CKPT)
The checkpoint process (CKPT) updates the control file and data file headers with checkpoint information and signals DBWn to write blocks to disk. Checkpoint information includes the checkpoint position, SCN, location in online redo log to begin recovery, and so on. As shown in Figure 15-4, CKPT does not write data blocks to data files or redo blocks to online redo log files.
When Oracle Database Initiates Checkpoints
The checkpoint process (CKPT) is responsible for writing checkpoints to the data file headers and control file. Checkpoints occur in a variety of situations. For example, Oracle Database uses the following types of checkpoints:
Tablespace and data file checkpoints
The database writes to disk all buffers modified by redo before a specific target. A tablespace checkpoint is a set of data file checkpoints, one for each data file in the tablespace. These checkpoints occur in a variety of situations, including making a tablespace read-only or taking it offline normal, shrinking a data file, or executing ALTER TABLESPACE BEGIN BACKUP.
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