[CALCITE-2974] Timestamp conversion performance can be improved

• Type: Improvement
• Status: Reopened
• Priority: Major
• Resolution: Unresolved
• Affects Version/s: 1.19.0
• Component/s: core
• Labels: easyfix performance
• Assignee: Unassigned
• Reporter: Valeriy Trofimov
• Created: 03/Apr/19 00:18
• Updated: 18/Jun/21 08:35

Description

RexSimplify.simplifyCast() is slow when converting a string to SQL Timestamp value. The slowness is caused by this line:

executor.reduce(rexBuilder, ImmutableList.of(e), reducedValues);

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:

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);
}

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?

Issue Links

• is related to: CALCITE-1695 Not all RexUtil.simplifyXxx code paths carry the provided executor