“线程”在“线程检查点”上下文中是什么意思？

Question

以下摘录来自Oracle 概念。也许这是一个愚蠢的问题，但我真的需要你的帮助来理解它。

我的问题是：

• 上下文线程检查点中的线程是什么意思？
• 这是否意味着重做日志线程（属于特定实例的所有重做日志文件）？
• 什么某个目标的手段？

谢谢大家！英语不是我的母语，我觉得完全理解这一点有点困难。

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: 

?   Thread checkpoints 
    ^^^^^^
    The database writes to disk all buffers modified by redo in a specific thread before  
                                                             ^^^^^^^^^^^^^^^^^^^^
    a certain target. The set of thread checkpoints on all instances in a database is 
    ^^^^^^^^^^^^^^^^^
    a database checkpoint. Thread checkpoints occur in the following situations: 

    – Consistent database shutdown 

    – ALTER SYSTEM CHECKPOINT statement 

    – Online redo log switch 

    – ALTER DATABASE BEGIN BACKUP statement 

?   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. 

?   Incremental checkpoints 

    An incremental checkpoint is a type of thread checkpoint partly intended to avoid  
    writing large numbers of blocks at online redo log switches. DBWn checks at least  
    every three seconds to determine whether it has work to do. When DBWn writes  
    dirty buffers, it advances the checkpoint position, causing CKPT to write the  
    checkpoint position to the control file, but not to the data file headers. 

Other types of checkpoints include instance and media recovery checkpoints and  
checkpoints when schema objects are dropped or truncated.

Answer 1

是的，这种情况下的线程是实例生成的重做。如果您有一个 4 节点 RAC，您将有 4 个重做线程。这是thread#在v$archived_log. 特定目标几乎肯定是指 SCN。