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https://issues.apache.org/jira/browse/CALCITE-2974?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16808397#comment-16808397
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Julian Hyde commented on CALCITE-2974:
--------------------------------------
We use compiled code because it was the simplest way to ensure correctness. If
we used an expression evaluator in RexSimplify, now we have two pieces of code
trying to do the same thing.
Can you share your performance measurements?
The scary thing is that if there is a performance problem here, then there are
many other expressions with similar problems. I'd like to have a plan to deal
with them also.
> Timestamp conversion performance can be improved
> ------------------------------------------------
>
> Key: CALCITE-2974
> URL: https://issues.apache.org/jira/browse/CALCITE-2974
> Project: Calcite
> Issue Type: Improvement
> Components: core
> Affects Versions: 1.19.0
> Reporter: Valeriy Trofimov
> Priority: Major
> Labels: easyfix, performance
> Fix For: next
>
> Original Estimate: 24h
> Remaining Estimate: 24h
>
> RexSimplify.simplifyCast() is slow when converting a string to SQL Timestamp
> value. The slowness is caused this line:
> {code:java}
> executor.reduce(rexBuilder, ImmutableList.of(e), reducedValues);
> {code}
> Debugging this code line with my team showed that for timestamp conversion it
> loads a pre-compiled conversion code, which makes it slow. My team proposes
> to replace this line with the following code that greately improves
> performance:
> {code:java}
> if (typeName == SqlTypeName.CHAR && e.getType().getSqlTypeName() ==
> SqlTypeName.TIMESTAMP_WITH_LOCAL_TIME_ZONE) {
> if (literal.getValue() instanceof NlsString) {
> String timestampStr = ((NlsString) literal.getValue()).getValue();
> Long timestampLong =
> SqlFunctions.toTimestampWithLocalTimeZone(timestampStr);
> reducedValues.add(rexBuilder.makeLiteral(timestampLong, e.getType(),
> true));
> }
> }
> if (reducedValues.isEmpty()) {
> executor.reduce(rexBuilder, ImmutableList.of(e), reducedValues);
> }
> {code}
> Let us know if we can submit a pull request with this code change or if we've
> missed anything. Do you know the reason behind using a pre-compiled code for
> timestamp conversion?
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