Oracle Internal之Block Cle…

原文地址：Oracle<wbr>Internal之Block<wbr>Cleanout<wbr>1</wbr></wbr></wbr> 作者：顾问

为什么会有Block Cleanouts? Oracle server在执行一个交易(transaction)时会保存交易数据在数据块(data block)本身，并且一个交易有可能修改大量的数据块,因此交易需要清理这些在数据块自己上的交易数据当一个交易完成commit。
那些东西需要cleaned out?
<wbr> 1. Row Locks<br><wbr> 2. ITL Entry:<br><wbr><wbr><wbr><wbr><wbr> - Commit flags<br><wbr><wbr><wbr><wbr><wbr> - Free Space Credit/Commit SCN<br><br> Deferred Block Cleanout:<br><wbr><wbr> A transaction commit was a simple update to the relevant undo segment header.<br><wbr><wbr> The data block cleanout was left to the next reader of the modified block<br> Fast Block Cleanout: This is the default action.<br><wbr><wbr> Modified blocks are 'memorized' by a transaction. On transaction commit, cleanout is attempted<br><wbr><wbr> on those blocks in memory(up to a limit 20 blocks). For any blocks above this threshold, or<br><wbr><wbr> aged out of memory, or currently pinned by another process deferred block cleanout will be<br><wbr><wbr> still used.<br></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr>