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From:Tim Gustafson Date:July 1 2010 4:22pm
Subject:Re: selecting data for computation
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> A general-case good design for this is to have status fields, as
> suggested, and who-owns-this-row fields.  Set the rows initially to
> un-owned (NULL), and status 'new' or similar.

The "get_lock" approach was ultimately successful, and I think better than
using a status field as it is entirely self-managing.  If one of the
compute clients die, its locks are immediately released and another
compute client can immediately pick up where it left off.  I just had to
separate the "get_lock" query from the "select" query for it to work.

I also optimized the select query by adding a "distance" column, and
setting that to "sqrt(pow(x, 2) + pow(y, 2))" and then ordering the select
clause by that column as opposed to running the function each time and
that sped up the select query to less than a second per run.

I also plan on changing the limit clause from "limit %d, 1" to something
like "limit 500" and then iterating through the results until I get one
that succeeds, as that is more efficient than running multiple select
queries.

Anyhow, thanks for all the good suggestions and pointers - it all worked
out in the end!

Tim Gustafson
831-332-1496
tjg@stripped
http://tgustafson.com/

Thread
selecting data for computationTim Gustafson24 Jun
  • Re: selecting data for computationDan Nelson24 Jun
    • Re: selecting data for computationTim Gustafson25 Jun
      • Re: selecting data for computationTim Gustafson25 Jun
        • Re: selecting data for computationDan Nelson25 Jun
          • Re: selecting data for computationTim Gustafson26 Jun
            • Re: selecting data for computationBaron Schwartz28 Jun
              • Re: selecting data for computationTim Gustafson1 Jul
      • Re: selecting data for computationJoerg Bruehe25 Jun