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From:Michael Dykman Date:November 4 2012 10:34pm
Subject:Re: UDF behaves non-deterministic
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A couple of questions present.

You mention that selecting from the whole table takes 5-10s so I assume you
have a lot of records.
  is the data not in flux? are you sure?
  these conflict queries are all on the same server?

i would have structured the query like so:
  select *, udf(column,'value') AS u from table order by u;

I suspect it might reduce the number of udf invocations..  the order by
clause is frequently referred to in the process of sorting.. keeping that
static instead of dynamic might sanitize your issue.

On 2012-11-04 4:24 PM, "Stefan Kuhn" <stefhk3@stripped> wrote:

Hi all,
I have a weired (for me at least) problem with a user defined function,
written in C. The function seems to return different results in different
runs (the code of the function does not contain random elements). Basically,
the function calculates a score based on a column in a table and an input
value. So I do something like this:
select * from table order by udf(column, 'input_value') desc;
For my understanding, this should give the same result always. But if I run
many statements (execution is from a java program and I can do it in
parallel
threads) so that they overlap (the udf on a large table takes 5-10 s on a
slow machine), the results of some queries are different. If I have enough
time between statements, it seems to work, i. e. the result is always the
same. I would have thought the statements are independent, even if executed
on different jdbc connections in parallel.
Does somebody have an idea?
Or could somebody give an idea on debugging? Normally I would try to debug
the
code to see what goes on, but how can I do this in a udf? Can I log in the
udf?
Thanks for any hints,
Stefan

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Thread
UDF behaves non-deterministicStefan Kuhn4 Nov
  • Re: UDF behaves non-deterministicDan Nelson5 Nov
  • Re: UDF behaves non-deterministicwalter harms5 Nov
  • Re: UDF behaves non-deterministichsv5 Nov
    • Re: UDF behaves non-deterministicStefan Kuhn5 Nov
Re: UDF behaves non-deterministicMichael Dykman4 Nov
  • Re: UDF behaves non-deterministicStefan Kuhn4 Nov