[
https://issues.apache.org/jira/browse/HIVE-5018?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13756731#comment-13756731
]
Benjamin Jakobus commented on HIVE-5018:
----------------------------------------
Here is some sample code:
{quote}
/**
* Examine the performance difference between declaring variables
inside loops
* and declaring them outside of loops.
*/
public class InLoopInstantiationTest {
public InLoopInstantiationTest() {
long start = System.currentTimeMillis();
SessionIdentifierGenerator gen = new SessionIdentifierGenerator();
for (int i = 0; i < 10000; i++) {
FooBar f = new FooBar();
Integer i1 = new Integer(i);
String s = gen.nextSessionId();
}
long end = System.currentTimeMillis();
System.out.println("in loop instantiation took " + (end - start) + "
milliseconds");
start = System.currentTimeMillis();
FooBar f;
Integer i1;
String s;
for (int i = 0; i < 10000; i++) {
f = new FooBar();
i1 = new Integer(i);
s = gen.nextSessionId();
}
end = System.currentTimeMillis();
System.out.println("avoiding in loop instantiation took " + (end -
start) + " milliseconds");
}
public static void main(String[] args) {
new InLoopInstantiationTest();
}
private class FooBar {
private String foo = "asdasdasdasdasdasdasdasdasdasdasdasdasdasdasdasd"
+ "asdasdasdasdasdasdasdasdasdasdasdasdasdasdasdasdasdasdasdasd"
+
"asdasdasdasdasdasdasdasdasdasdasdasdasdasdasdasdasdasdasdasd";
}
public final class SessionIdentifierGenerator {
private SecureRandom random = new SecureRandom();
public String nextSessionId() {
return new BigInteger(130, random).toString(32);
}
}
}
{quote}
The arithmetic script that I used to test this code in Hive is:
{quote}
SELECT (dataset.age * dataset.gpa + 3) AS F1, (dataset.age/dataset.gpa - 1.5)
AS F2
FROM dataset
WHERE dataset.gpa > 0;
{quote}
> Avoiding object instantiation in loops (issue 6)
> ------------------------------------------------
>
> Key: HIVE-5018
> URL: https://issues.apache.org/jira/browse/HIVE-5018
> Project: Hive
> Issue Type: Sub-task
> Reporter: Benjamin Jakobus
> Assignee: Benjamin Jakobus
> Priority: Minor
> Fix For: 0.12.0
>
> Attachments: HIVE-5018.1.patch.txt
>
>
> Object instantiation inside loops is very expensive. Where possible, object
> references should be created outside the loop so that they can be reused.
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