Julian Hyde created CALCITE-3517:
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Summary: DiffRepository spends too much time writing XML, makes
some tests 5x slower
Key: CALCITE-3517
URL: https://issues.apache.org/jira/browse/CALCITE-3517
Project: Calcite
Issue Type: Bug
Reporter: Julian Hyde
Tests that use {{DiffRepository}} are spending far too much effort writing XML,
even if the XML matches the reference file. For example, If I comment out [a
call to set(tag,
next)|https://github.com/apache/calcite/blob/ee83efd360793ef4201f4cdfc2af8d837b76ca69/core/src/test/java/org/apache/calcite/test/DiffRepository.java#L267],
{{RelOptRulesTest}} improves from 32s to 6s; {{SqlToRelConverterTest}}
improves from 24s to 4.7s; {{SqlPrettyWriterTest}} remains .8s.
The {{DiffRepository.expand}} method is the cause of the inefficiency. It
causes the entire XML document to be re-generated and written to disk. This is
not just slow but quadratic - if a test has N cases, each test writes the XML
document, an effort proportional to N.
{{DiffRepository}} should remain conservative. If one of the tests fails, and a
later test crashes, the output from the failed test should have been written
out. It is acceptable if the test remains slow if there are test failures.
{{DiffRepository}} is only used in tests; this bug does not affect production
code.
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