August 2015
Intermediate to advanced
312 pages
7h 28m
Japanese
Content preview from 初めてのSpark
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162
8 章 Spark のチューニングとデバッグ
こちらはシャッフル操作を避けるので、
repartition()
よりも効率的です。並列度が高すぎたり低
すぎたりしていると考えられる場合、こうした操作によってデータを配分し直すことができます。
例えば、大量のデータを
S3
から読み取り、その直後に
filter()
操作を行って、データセット
の内容をほとんどフィルタリングしてしまい、わずかな部分だけを取り出すとしましょう。デフォ
ルトでは、
filter()
が返す
RDD
は親と同じサイズを持つので、空のパーティションや、小さな
パーティションが大量にできてしまうかもしれません。この場合、もっとパーティション数が少な
い
RDD
になるようにパーティションを合併し直せば、アプリケーションのパフォーマンスを改善
できるかもしれません。
8-11
をご覧ください。
8-11
PySpark
RDD
#
数
1,000
ファイルにマッチするかもしれないワイルドカードの入力
>>> input = sc.textFile("s3n://log-files/2014/*.log")
>>> input.getNumPartitions()
35154
#
ほとんどすべてのデータを除外するフィルタ
>>> lines = input.filter(lambda line: line.startswith("2014-10-17"))
>>> lines.getNumPartitions()
35154
#
キャッシングの前に ...
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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.