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When a transaction is committed, the following occurs:
事务结束之后触发的事件：
1. The internal transaction table for the associated undo tablespace records that the
transaction has committed, and the corresponding unique system change number
(SCN) of the transaction is assigned and recorded in the table.
2. The log writer process (LGWR) writes redo log entries in the SGA’s redo log
buffers to the redo log file. It also writes the transaction’s SCN to the redo log file. This atomic event constitutes the commit of the transaction.
3. Oracle releases locks held on rows and tables.
4. Oracle marks the transaction complete.
Note: The default behavior is for LGWR to write redo to the online
redo log files synchronously and for transactions to wait for the redo
to go to disk before returning a commit to the user. However, for
lower transaction commit latency application developers can specify
that redo be written asynchronously and that transactions do not need
to wait for the redo to be on disk.
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