Ask HN: How to read a terabyte flat file

https://news.ycombinator.com/item?id=861433

by calgaryo • 17 years ago

2 5 17 years ago

news.ycombinator.com

For some reason - an application spews some results into a single file. What do you think would be the best way of reading (multiple) from the file?

gdp2• 17 years ago

I don't think I understand the question. Are you actually asking how to read from a terabyte flat file, or are you asking how to process a terabyte of sequential data? They are two (related) but distinct questions.

tamersalama• 17 years ago

Sorry for not being clear the first time. Proper processing is what I'm after. The reading has to be accompanied by parsing. The file is divided into sections, and each section will have its own parsing / user-actions / processing / output.

gdp2• 17 years ago

Well, the main thing would be to operate in a store-nothing kind of way. There has to be a fixed amount of storage required no matter what the length of the input is. You'll need to keep aggregate totals and compute over each row, as opposed to storing any data.

The parsing should be simple. Lex and/or Yacc should handle very large files. If not, you can always write something by hand, once again sticking to the store-nothing principle.

I would think about it as a fold operation (http://en.wikipedia.org/wiki/Fold_%28higher-order_function%2...) over the lines in the file, where the parser state and any aggregate calculated values are stored in the accumulator, and each new line is considered in conjunction with the current state and the previous calculated values.

wmf• 17 years ago

First, get the file into Hadoop. From there the parsing and processing should be easier.

nshah• 17 years ago

Depending on language restrictions, you may be able to implement read streams that make a pass through the file and create appropriate call-backs when hitting each section...

Ask HN: How to read a terabyte flat file

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