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https://issues.apache.org/jira/browse/CALCITE-2974?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16812871#comment-16812871
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Valeriy Trofimov commented on CALCITE-2974:
-------------------------------------------
Our perf numbers are based on running selected code from
SqlOperatrBaseTest.testCastDateTime() thousands of times on an instrumented
RexSimplify.simplifyCast() method. For the previously mentioned timestamp
conversion the difference is 4-7 fold perf improvement:
|| ||Current Code||Improved Code||Improvement Ratio||
||Tp50|51,403|11,454|4.48|
||Tp90|119,010|17,880|6.65|
||Tp99|174,603|37,435|4.66|
If you add similar code for string-to-int conversion you'll get 7-14 fold perf
improvement:
|| ||Current Code||Improved Code||Improvement Ratio||
||Tp50|32,406|4,470|7.24|
||Tp90|85,486|6,146|13.90|
||Tp99|132,698|10,337|12.83|
The numbers for the "Current Code" and "Improved Code" are time in nanoseconds
how long it took to execute the current code line in question (call to call to
reduce()) and the improved code where we manually convert string to timestamp
or int.
> 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 by 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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