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  • ORACLE的主要进程DBWn,LGWR的工作原理

    DBWn defers writing to the data files until one of the following events occurs:
    1. Incremental or normal checkpoint
    2.The number of dirty buffers reaches a threshold value
    3. A process scans a specified number of blocks when scanning for free buffers and cannot find any
    4. Timeout occurs
    5.A ping request in Real Application Clusters (RAC) environment
    6.Placing a normal or temporary tablespace offline
    7.Placing a tablespace in read-only mode
    8.Dropping or truncating a table
    9. ALTER TABLESPACE tablespace name BEGIN BACKUP

    LGWR performs sequential writes from the Redo Log Buffer to the online redo log file under the following situations:
    1. When a transaction commits
    2.When the Redo Log Buffer is one-third full
    3.When there is more than 1 MB of changes recorded in the Redo Log Buffer
    4.Before DBWn writes modified blocks in the Database Buffer Cache to the data files
    5. Every three seconds

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  • 原文地址:https://www.cnblogs.com/caibird2005/p/1378160.html
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