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Re: hashing strings to integers for sqlite3 keys

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On 2014-05-22, Chris Angelico wrote:

> On Thu, May 22, 2014 at 9:47 PM, Adam Funk <a24061@ducksburg.com> wrote:
>> I'm using Python 3.3 and the sqlite3 module in the standard library.
>> I'm processing a lot of strings from input files (among other things,
>> values of headers in e-mail & news messages) and suppressing
>> duplicates using a table of seen strings in the database.
>>
>> It seems to me --- from past experience with other things, where
>> testing integers for equality is faster than testing strings, as well
>> as from reading the SQLite3 documentation about INTEGER PRIMARY KEY
>> --- that the SELECT tests should be faster if I am looking up an
>> INTEGER PRIMARY KEY value rather than TEXT PRIMARY KEY.  Is that
>> right?
>
> It might be faster to use an integer primary key, but the possibility
> of even a single collision means you can't guarantee uniqueness
> without a separate check. I don't know sqlite3 well enough to say, but
> based on what I know of PostgreSQL, it's usually best to make your
> schema mimic your logical structure, rather than warping it for the
> sake of performance. With a good indexing function, the performance of
> a textual PK won't be all that much worse than an integral one, and
> everything you do will read correctly in the code - no fiddling around
> with hashes and collision checks.
>
> Stick with the TEXT PRIMARY KEY and let the database do the database's
> job. If you're processing a really large number of strings, you might
> want to consider moving from sqlite3 to PostgreSQL anyway (I've used
> psycopg2 quite happily), as you'll get better concurrency; and that
> might solve your performance problem as well, as Pg plays very nicely
> with caches.

Well, actually I'm thinking about doing away with checking for
duplicates at this stage, since the substrings that I pick out of the
deduplicated header values go into another table as the TEXT PRIMARY
KEY anyway, with deduplication there.  So I think this stage reeks of
premature optimization.


-- 
The history of the world is the history of a privileged few.
                                            --- Henry Miller

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hashing strings to integers for sqlite3 keys Adam Funk <a24061@ducksburg.com> - 2014-05-22 12:47 +0100
  Re: hashing strings to integers for sqlite3 keys Peter Otten <__peter__@web.de> - 2014-05-22 14:58 +0200
    Re: hashing strings to integers for sqlite3 keys Adam Funk <a24061@ducksburg.com> - 2014-05-22 14:41 +0100
      Re: hashing strings to integers for sqlite3 keys Chris Angelico <rosuav@gmail.com> - 2014-05-23 00:08 +1000
        Re: hashing strings to integers for sqlite3 keys Adam Funk <a24061@ducksburg.com> - 2014-05-22 15:40 +0100
  Re: hashing strings to integers for sqlite3 keys Chris Angelico <rosuav@gmail.com> - 2014-05-22 23:03 +1000
    Re: hashing strings to integers for sqlite3 keys Adam Funk <a24061@ducksburg.com> - 2014-05-22 14:47 +0100
  Re: hashing strings to integers for sqlite3 keys Tim Chase <python.list@tim.thechases.com> - 2014-05-22 08:09 -0500
    Re: hashing strings to integers for sqlite3 keys Adam Funk <a24061@ducksburg.com> - 2014-05-22 14:54 +0100
      Re: hashing strings to integers for sqlite3 keys Chris Angelico <rosuav@gmail.com> - 2014-05-23 00:14 +1000
        Re: hashing strings to integers for sqlite3 keys Adam Funk <a24061@ducksburg.com> - 2014-05-22 15:47 +0100
          Re: hashing strings to integers for sqlite3 keys Chris Angelico <rosuav@gmail.com> - 2014-05-23 01:09 +1000
          Re: hashing strings to integers for sqlite3 keys Peter Otten <__peter__@web.de> - 2014-05-22 17:34 +0200
            hashing strings to integers (was: hashing strings to integers for sqlite3 keys) Adam Funk <a24061@ducksburg.com> - 2014-05-23 11:27 +0100
              Re: hashing strings to integers Adam Funk <a24061@ducksburg.com> - 2014-05-23 11:36 +0100
                Re: hashing strings to integers Chris Angelico <rosuav@gmail.com> - 2014-05-23 21:01 +1000
              Re: hashing strings to integers (was: hashing strings to integers for sqlite3 keys) Chris Angelico <rosuav@gmail.com> - 2014-05-23 20:59 +1000
                Re: hashing strings to integers Adam Funk <a24061@ducksburg.com> - 2014-05-27 16:13 +0100
                Re: hashing strings to integers Steven D'Aprano <steve+comp.lang.python@pearwood.info> - 2014-05-27 17:02 +0000
                Re: hashing strings to integers Chris Angelico <rosuav@gmail.com> - 2014-05-28 05:16 +1000
                Re: hashing strings to integers Dan Sommers <dan@tombstonezero.net> - 2014-05-28 01:55 +0000
                Re: hashing strings to integers Adam Funk <a24061@ducksburg.com> - 2014-06-03 11:29 +0100
                Re: hashing strings to integers Adam Funk <a24061@ducksburg.com> - 2014-06-03 11:32 +0100
              Re: hashing strings to integers Terry Reedy <tjreedy@udel.edu> - 2014-05-23 15:10 -0400
                Re: hashing strings to integers Adam Funk <a24061@ducksburg.com> - 2014-05-27 16:20 +0100
  Re: hashing strings to integers for sqlite3 keys alister <alister.nospam.ware@ntlworld.com> - 2014-05-22 14:48 +0000

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