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Google ファイル システム (GFS) の論文を読み終えたところです。この論文によると、GFSは

optimized for appending operations rather than random writes.

この特徴が論文全体で強調されているのを見ると、非常に重要であるに違いないと思います。

まったく就労経験のない学生として、Appending OperationsGoogle が語るそのような実生活の例は何ですか? かなり強烈に聞こえます。

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It is a central limitation of the Google File System. It contrasts it from general purpose parallel file systems like GPFS. However, it makes to design a lot easier when it comes e.g. to replication. As Google is able to design its application around its file system and because random operations are inherently slow (on rotating media), this is fine for them.

Tons of things are "append" operations:

  • New log entries are appended to a log file. (GoogleFS can also append to an already closed file (with certain limitations, the very similar http://hadoop.apache.org/hdfs/ is not able to do that).
  • New web crawl data is appended to a crawl file instead of overwriting existing versions of the crawl within a file.
  • All MapReduce (you should also read that paper) outputs are writing a file from the beginning to the end, appending key/value pairs to the file(s).
  • ...

All writes to a file not updating data in the middle of the file using a seek or a pwrite operations are appends. The most important usage of random writes are (classical) database backends.

于 2012-01-08T21:08:14.940 に答える