Which two events always request the LGWR to write?
A)When DBWn writes dirty buffers.
B)When a log switch occurs.
C)When a checkpoint occurs.
D)When LGWR is notified by a server process that performs a COMMIT or ROLLBACK.
E)When PMON restarts a serve process.
Answer: AD
趙:AB=>AD
LGWR 觸發 5 條件
LGWR 進程將日誌緩衝區的日誌信息寫入聯機日誌文件,觸發的 5 個條件:
一、前臺進程觸發
1.用戶發出 commit,rollback 語句。
2.日誌緩衝區找不到足夠的內存來放日誌信息。
二、每隔 3 秒鐘。(3 秒)
三、日誌信息的數量達到日誌緩衝區的 1/3。(1/3 滿)
四、日誌信息數量達到 1MB。(1M)
五、DBWn 啓動時,如果發現有髒數據塊對應的重做條目還沒寫到聯機日誌文件,則觸發 LGWR,並等 LGWR 寫完,DBWn 才繼續。(DBWn 寫髒 buffer)