Igor Lozynskyi created CALCITE-4494:
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Summary: Improve planning performance with RelSubset check for
Rel presence
Key: CALCITE-4494
URL: https://issues.apache.org/jira/browse/CALCITE-4494
Project: Calcite
Issue Type: Improvement
Components: core
Affects Versions: 1.26.0
Environment: All environments
Reporter: Igor Lozynskyi
Fix For: 1.27.0
Attachments: CalcitePerf_Planning_RelList_consumes_a_lot.png,
CalcitePerf_Planning_TPCH_Q7_RelList_consumes_a_lot.png,
CalcitePerf_Planning_after_improvements.png
*Problem*
Currently, the planning process shows a performance degradation when comparing
to version 1.25. Worse palling time seems to affect most queries, but it is
especially clear for queries with many Rel nodes (especially with multiple
joins).
In a downstream project, we have a stress test that checks the planning time.
In some cases, the planning time is increased by x4 (for a query with 28 joins).
The main contributing factor (but not the only one) for the slow-down could be
traced to
[https://github.com/apache/calcite/pull/2222/files|[https://github.com/apache/calcite/pull/2222/files].]
*Potential Solution*
As it was mentioned by the reviewers, we may improve the current situation with
some tiny changes:
* Introduce a method to check that a Rel node belongs to the RelSubset instead
of getting all Rel nodes (the current code may take up to 60% of the planning
time).
* Improve the null check in RelMdPredicates by building an error message in
RelMdPredicates.ExprsItr only when it is required (may additionally take 10% of
the planning time due to SortedMap.toString() being expensive when frequently
called).
With these 2 changes, I was able to regain most of the lost planning
performance.
The following flame graph clearly shows that the call to RelSubset.getRelList()
from VolcanoRuleCall.onMatch() is expensive:
!CalcitePerf_Planning_RelList_consumes_a_lot.png!
After the proposed improvements, the flame graph shows the following:
!CalcitePerf_Planning_after_improvements.png!
It is clear that the HintStrategyTable.isRuleExcluded() call is expensive, but
the overall picture is much better.
Also, in my environment, the TPC-H Q7 test takes ~20% less time (39.6 sec vs
32.9 sec) after the proposed improvements. Here, the flame graph also shows
that ordinary queries are also affected by the redundant RelSubset.getRelList()
calls:
!CalcitePerf_Planning_TPCH_Q7_RelList_consumes_a_lot.png!
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