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https://issues.apache.org/jira/browse/CALCITE-3878?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=17069000#comment-17069000
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Julian Hyde commented on CALCITE-3878:
--------------------------------------
I wish we didn't have to spend time on this, too. Believe, me I have better
things.
The following code is not an improvement:
{code:java}
@Override public RelNode convert(RelNode rel) {
LogicalJoin join = (LogicalJoin) rel;
List<RelNode> newInputs = new ArrayList<>(join.getInputs().size());
for (RelNode input : join.getInputs()) {
{code}
because joins have only 2 inputs.
bq. Note: you are right the hotspots will show in the profiling, however: 1)
Noone profiles Calcite
The principle is that that code is not performance critical unless proven
otherwise. In 98% of our code, clarity is more important than performance.
By accepting this fix, we are accepting the principle that {{new ArrayList()}}
without a size is wrong. It is not wrong. We are writing in a high-level
language.
I do agree with you that a modern 'functional' style can be clear,
non-redundant and performant.
> 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: 1h 10m
> 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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