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https://issues.apache.org/jira/browse/CALCITE-3878?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=17068401#comment-17068401
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neoremind commented on CALCITE-3878:
------------------------------------
[~vladimirsitnikov] I update the code to return list, the result looks pretty
much the same.
{code:java}
Benchmark
(size) Mode Cnt Score Error Units
ArrayListTest.testWithInitialCapacity
256 avgt 4 1918.284 ± 1384.469 ns/op
ArrayListTest.testWithInitialCapacity:·gc.alloc.rate
256 avgt 4 492.327 ± 330.941 MB/sec
ArrayListTest.testWithInitialCapacity:·gc.alloc.rate.norm
256 avgt 4 1064.000 ± 0.001 B/op
ArrayListTest.testWithInitialCapacity:·gc.churn.PS_Eden_Space
256 avgt 4 492.318 ± 336.778 MB/sec
ArrayListTest.testWithInitialCapacity:·gc.churn.PS_Eden_Space.norm
256 avgt 4 1063.841 ± 37.935 B/op
ArrayListTest.testWithInitialCapacity:·gc.churn.PS_Survivor_Space
256 avgt 4 0.131 ± 0.354 MB/sec
ArrayListTest.testWithInitialCapacity:·gc.churn.PS_Survivor_Space.norm
256 avgt 4 0.280 ± 0.630 B/op
ArrayListTest.testWithInitialCapacity:·gc.count
256 avgt 4 339.000 counts
ArrayListTest.testWithInitialCapacity:·gc.time
256 avgt 4 183.000 ms
ArrayListTest.testWithoutInitialCapacity
256 avgt 4 2354.479 ± 572.751 ns/op
ArrayListTest.testWithoutInitialCapacity:·gc.alloc.rate
256 avgt 4 1699.781 ± 415.378 MB/sec
ArrayListTest.testWithoutInitialCapacity:·gc.alloc.rate.norm
256 avgt 4 4544.000 ± 0.001 B/op
ArrayListTest.testWithoutInitialCapacity:·gc.churn.PS_Eden_Space
256 avgt 4 1706.059 ± 392.494 MB/sec
ArrayListTest.testWithoutInitialCapacity:·gc.churn.PS_Eden_Space.norm
256 avgt 4 4561.142 ± 197.365 B/op
ArrayListTest.testWithoutInitialCapacity:·gc.churn.PS_Survivor_Space
256 avgt 4 0.113 ± 0.054 MB/sec
ArrayListTest.testWithoutInitialCapacity:·gc.churn.PS_Survivor_Space.norm
256 avgt 4 0.302 ± 0.100 B/op
ArrayListTest.testWithoutInitialCapacity:·gc.count
256 avgt 4 378.000 counts
ArrayListTest.testWithoutInitialCapacity:·gc.time
256 avgt 4 214.000 ms
{code}
> Make ArrayList creation with initial capacity when size is fixed
> ----------------------------------------------------------------
>
> Key: CALCITE-3878
> URL: https://issues.apache.org/jira/browse/CALCITE-3878
> Project: Calcite
> Issue Type: Improvement
> Components: core
> Affects Versions: 1.22.0
> Reporter: neoremind
> Priority: Minor
> Labels: pull-request-available
> Time Spent: 40m
> Remaining Estimate: 0h
>
> I find many places in Calcite where _new ArrayList<>()_ is used, if the list
> is expected to be immutable or not resizing, it is always a good manner to
> create with initial capacity, better for memory usage and performance.
> I search all occurrences, focus on the core module, to make it safe, I only
> update local variables with fixed size and not working in recursive method.
> If the local variable reference goes out of scope, if resizing is needed,
> things will work normally as well, so no side effect, but for the "escaping"
> case, I am very conservative and do not change them.
>
>
>
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