Oracleはどうやって行の可視性を決定しているのでしょうか？たとえば行を挿入した時に、PostgreSQL同様挿入したトランザクションのxidを行に一緒に書いていると思うのですが、そのトランザクションが走行中なのか、すでにコミットしたのかはどこに書いてあるのでしょう？
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As I understand it, there are "interesting transaction lists" (ITLs) in each block -- a fixed list of XIDs, along with a small amount of associated metadata for each. Both index blocks and heap blocks have ITLs.
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Thank you very much for the quick answer. It's interesting that Oracle has the data on disk rather than in memory like PostgreSQL.
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As I understand it, the undo can be stored in the buffer pool, so it's not quite in memory in the simplest sense. (I am really not sure of the details, though.)