January 2021
Intermediate
240 pages
5h 32m
Japanese
Content preview from 図解まるわかり データベースのしくみ
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126
２つの処理が競合して
処理が止まる問題
4-17
複数のトランザクション処理が同時に同じデータを操作することで、互
いに相手の処理終了を待つ状態となり、次の処理へ進めなくなってしまう
ことをデッドロックと呼びます。
銀行口座の例で考えてみます。A口座と B口座に 10 万円ずつ入っている
状態で図4-33 のような「A口座からB口座に10 万円の送金を行うアクシ
ョン」と「B口座から A口座に 10万円の送金を行うアクション」が同時に
実行されたとします。まず1-1 の「A口座の預金をマイナス10 万円にす
る」という処理が実行されると、コミットが行われるまでA 口座のデータ
はロックされた状態となります。このようにトランザクション中の処理に
関わるデータは一時的にロックされます。もし
されます。その後1-2 が実行される前に、2-1の「B口座の預金を
マイナス10 万円にする」が実行されました。同様にしてB口座のデータ
がロックされます。すると、2 つのトランザクションがお互いに相手が操
作したいデータをロックしていて1-2 と 2-2 の処理を進められず、どちら
のアクションも止まってしまいました。これがデッドロックです。
デッドロックが起こった場合、させなければ
なりません。データベース管理システムによっては自動的にデッドロック
を監視して、ロールバックを行うしくみもありますが、そもそもデッドロ ...
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O’Reilly covers everything we've got, with content to help us build a world-class technology community, upgrade the capabilities and competencies of our teams, and improve overall team performance as well as their engagement.Julian F.
I wanted to learn C and C++, but it didn't click for me until I picked up an O'Reilly book. When I went on the O’Reilly platform, I was astonished to find all the books there, plus live events and sandboxes so you could play around with the technology.Addison B.
I’ve been on the O’Reilly platform for more than eight years. I use a couple of learning platforms, but I'm on O'Reilly more than anybody else. When you're there, you start learning. I'm never disappointed.Amir M.
I'm always learning. So when I got on to O'Reilly, I was like a kid in a candy store. There are playlists. There are answers. There's on-demand training. It's worth its weight in gold, in terms of what it allows me to do.