A pure perl solution that results in an average lookup time of < 1/2 a millisecond per record.

This indexes the 30GB/160e6 record file in around 45 minutes. (10 lines):

<Reveal this spoiler or all spoilers in this node or all in this thread>

And this loads the 2GB index into memory, uses a binary search to find the index entry, seek to locate and readline to read the record. (50 lines)

<Reveal this spoiler>
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In reply to Re: Using indexing for faster lookup in large file (PP < 0.0005s/record) by BrowserUk
in thread Using indexing for faster lookup in large file by anli_

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