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https://issues.apache.org/jira/browse/TRAFODION-2912?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
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Work on TRAFODION-2912 started by Hans Zeller.
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> Non-deterministic scalar UDFs not executed once per row
> -------------------------------------------------------
>
> Key: TRAFODION-2912
> URL: https://issues.apache.org/jira/browse/TRAFODION-2912
> Project: Apache Trafodion
> Issue Type: Bug
> Components: sql-cmp
> Affects Versions: 2.0-incubating
> Reporter: Hans Zeller
> Assignee: Hans Zeller
> Priority: Major
> Fix For: 2.3
>
>
> This problem was found by Andy Yang.
> Andy created a random generator scalar UDF and found that it did not return a
> different random value for each row:
> {noformat}
> >>select scalar_rand_udf(), scalar_rand_udf()
> +>from (values (1), (2), (3)) T(s);
> RND RND
> ----------- -----------
> 846930886 1804289383
> 846930886 1804289383
> 846930886 1804289383
> --- 3 row(s) selected.
> >>
> {noformat}
> Here is the explain, it shows that we are using hash joins, not nested joins,
> to evaluate the UDFs:
> {noformat}
> >>explain options 'f' s;
> LC RC OP OPERATOR OPT DESCRIPTION CARD
> ---- ---- ---- -------------------- -------- -------------------- ---------
> 5 . 6 root 3.00E+000
> 4 1 5 hybrid_hash_join 3.00E+000
> 3 2 4 hybrid_hash_join 1.00E+000
> . . 3 isolated_scalar_udf SCALAR_RAND_UDF 1.00E+000
> . . 2 isolated_scalar_udf SCALAR_RAND_UDF 1.00E+000
> . . 1 tuplelist 3.00E+000
> --- SQL operation complete.
> >>
> {noformat}
> The problem is that we don't check for non-deterministic UDFs when we
> transform a TSJ to a regular join in the transformer or normalizer. We don't
> even set the non-deterministic flag in the group attributes of the
> IsolatedScalarUDF node.
> The fix is to set this flag correctly and to add a check and not transform
> routine joins for non-deterministic isolated scalar UDFs into a regular join.
>
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