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Mandatory background story

I had an end-of-day job that was taking too much time, and it turns out that the problem was retrieving the closing time values from several textual log files, using a sequential scan.

I knew the answer was to do a binary search, but I was fairly certain someone else HAD to have run into this problem before, so I typed text file binary search in the Search box here, and got Binary Searches on Sorted Text Files.

runrig's reply in that thread pointed me to File::SortedSeek.

Module overview

File::SortedSeek implements binary searches through large sorted text files, using string, numeric, or timestamp keys.

It's ideal for finding a particular time in large logs, for instance.

The module was authored by Dr. James Freeman, better known around here as tachyon.

Usage example

The files I have to deal with use a non-standard integer timestamp. Each line looks like

{timestamp} {value} {value} {value} {value}

Using the module to find the right line couldn't be easier!

#!/usr/bin/perl -w use strict; use File::SortedSeek ':all'; my $targetTS=1234567789; # for instance open(FILE,"<") or die "Can't open, error $!"; # File::SortedSeek::numeric looks for a numeric key # It takes an optional sub ref argument to "massage" the # line from the file to extract the key. numeric(*FILE,$targetTS,sub {$_[0]=~/^\s*(\d+)/ or return 0; return $1 +}); # this will return the line that matches $targetTS, or the first line +> $line=<FILE>; close(FILE);


tachyon rules!!! :)

In reply to File::SortedSeek by RMGir

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    [Corion]: ... in Pg, but that would mean that I'd have to deal with credentials and stuff :)
    [Corion]: In fact, the whole thing is just four simple programs, one App::scrape, another being DBIx::RunSQL, and one some glue to convert a JSON object into an SQL INSERT statement (+DBI connect/execute), so it would be an incredibly simple solution...
    [Corion]: ... but that simplicity falls down due to SQLite letting me down and me being too lazy to move to a real DB. Maybe DBD::CSV can handle window functions...
    [hippo]: Pg has the "trust" mechanism if you don't fancy using credentials for a trivial db.
    [Corion]: hippo: Oooh, that sounds quite nice - let me read the documentation on that :)
    [hippo]: https://www. docs/current/ static/auth- methods.html#AUTH- TRUST
    [erix]: or compile & run an instance as yourself (not user 'postgres')
    [erix]: easiest setup is to run with PG* env variables set, and a custom .pgpass files (can be a $PGPASSFILE)
    [Corion]: Hmm - "trust" sounds interesting, but I have still to find whether I can restrict that on a per-DB level ;)
    [Corion]: erix: Sure, but SQLite doesn't even need that :)

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