Log Writer Process (LGWR) (115)

The log writer process (LGWR) is responsible for redo log buffer
management—writing the redo log buffer to a redo log file on disk. LGWR writes all
redo entries that have been copied into the buffer since the last time it wrote.
The redo log buffer is a circular buffer. When LGWR writes redo entries from the redo
log buffer to a redo log file, server processes can then copy new entries over the entries
in the redo log buffer that have been written to disk. LGWR normally writes fast
enough to ensure that space is always available in the buffer for new entries, even
when access to the redo log is heavy.
LGWR writes one contiguous portion of the buffer to disk. LGWR writes:
■ A commit record when a user process commits a transaction
■ Redo log buffers
– Every three seconds
– When the redo log buffer is one-third full
– When a DBWn process writes modified buffers to disk, if necessary

日誌寫程式
1. 將重做日誌緩衝區的資料寫入重做日誌
2. 以下情況下 , LGWR開始寫:
當使用者提交事務 , 每三秒 , 重做日誌快取區1/3滿 , 還有可能DBWn寫髒modified buffers to disk

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